EEEB1073 Signal Generators and Oscilloscopes PDF

EEEB1073 Measurement & Instrumentation Topic 6: Signal Generator and Oscilloscopes  6.1 Signal Generator 6.2 Function Generator 6.3 Oscilloscope 6.4 D...

EEEB1073 Measurement & Instrumentation Topic 6: Signal Generator and Oscilloscopes  6.1 Signal Generator 6.2 Function Generator 6.3 Oscilloscope 6.4 Digital Oscilloscope Sub-Topics Main Reference: 1. Electronic Instrumentation and Measurement, 4th Edition, H.S. Kalsi., McGraw Hill, 2019 [Chapter 8] 2. Measurement and Instrumentation: Theory and Application, 2nd Edition, Alan S. Morris, Reza Langari, Academic Press, Elsevier, 2020. [Chapter 7 & 8] EEEB1073: Topic 6: Signal Generator and 2 Oscilloscopes 6.1 Signal Generators 6.1.1 Introduction The term oscillator is used to describe an instrument that provides only a sinusoidal output signal, and the term generator to describe an instrument that provides several output waveforms. A signal generator is one of a class of electronic devices that generates electrical signals / sine wave with set properties of amplitude, frequency, and wave shape. These generated signals are used as a stimulus for electronic measurements, typically used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well. EEEB1073: Topic 6: Signal Generator and 3 Oscilloscopes 6.1 Signal Generators 6.1.1 Introduction There are various types of signal generators, but several requirements are common to all types. The frequency of the signal should be known and stable. The amplitude should be controllable from very small to relatively large values. Finally, the signal should be distortion-free. When an oscillator generates a signal, no energy is created; it is simply converted from a dc source into ac energy at some specific frequency. There are many different types of signal generators with different purposes and applications and at varying levels of expense. EEEB1073: Topic 6: Signal Generator and 4 Oscilloscopes 6.1 Signal Generators 6.1.1 Introduction EEEB1073: Topic 6: Signal Generator and 5 Oscilloscopes 6.1 Signal Generators 6.1.1 Introduction Various kinds of signals, at both audio and radio frequencies, are required at various times in an instrumentation system. The frequency band limits, as defined by International Telecommunication Union (ITU): EEEB1073: Topic 6: Signal Generator and 6 Oscilloscopes  The frequency bands for 3G, 4G, and 5G used by major Malaysian telcos: Frequency Range Frequency Range Network Band Operators (Uplink) (Downlink) CelcomDigi, Maxis, U 3G 900 MHz (Band 8) 880 – 915 MHz 925 – 960 MHz Mobile CelcomDigi, Maxis, U 2100 MHz (Band 1) 1920 – 1980 MHz 2110 – 2170 MHz Mobile Maxis, CelcomDigi, U 4G 700 MHz (Band 28) 703 – 748 MHz 758 – 803 MHz Mobile, Unifi Mobile, Yes 850 MHz (Band 5) 824 – 849 MHz 869 – 894 MHz Unifi Mobile CelcomDigi, Maxis, U 900 MHz (Band 8) 880 – 915 MHz 925 – 960 MHz Mobile CelcomDigi, Maxis, U 1800 MHz (Band 3) 1710 – 1785 MHz 1805 – 1880 MHz Mobile CelcomDigi, Maxis, U 2100 MHz (Band 1) 1920 – 1980 MHz 2110 – 2170 MHz Mobile 2300 MHz (Band 40) 2300 – 2400 MHz (TDD) N/A Unifi Mobile, Yes CelcomDigi, Maxis, U 2600 MHz (Band 7) 2500 – 2570 MHz 2620 – 2690 MHz Mobile 2600 MHz (Band 38) 2570 – 2620 MHz (TDD) N/A Unifi Mobile, Yes Maxis, CelcomDigi, U 5G 700 MHz (Band n28) 703 – 748 MHz 758 – 803 MHz Mobile, Unifi Mobile, Yes Maxis, CelcomDigi, U 3500 MHz (Band n78) 3300 – 3800 MHz (TDD) N/A Mobile, Unifi Mobile, Yes Maxis, CelcomDigi, U 26 GHz (Band n258) 24.25 – 27.5 GHz (TDD) N/A Mobile, Unifi Mobile, Yes  TDD (Time Division Duplex) indicates the same frequency is used for both uplink and downlink, separated by time.  FDD (Frequency Division Duplex) uses different frequencies for uplink and downlink. EEEB1073: Topic 6: Signal Generator and 7 Oscilloscopes  Uplink and downlink refer to the directions in which data is transmitted between a mobile device and a network tower: 1. Uplink: This is the transmission of data from the mobile device to the network tower (or base station). It involves sending signals, such as voice or data, from the user’s phone up to the cell tower. Uplink frequencies are typically lower to reduce battery usage on the mobile device. 2. Downlink: This is the transmission of data from the network tower to the mobile device. It involves sending signals, like incoming calls, messages, or data, from the tower down to the user's phone. Downlink frequencies are often higher than uplink frequencies to ensure a stronger signal reception on the device. In summary:  Uplink = Device to Tower (Upstream)  Downlink = Tower to Device (Downstream) This division helps prevent interference and ensures that communication is smooth and continuous in both directions. EEEB1073: Topic 6: Signal Generator and 8 Oscilloscopes  Wi-Fi frequency bands used in Malaysia: Frequency Band Frequency Range Characteristics Broad coverage, good wall 2.4 GHz 2.4 – 2.4835 GHz penetration, more interference due to other devices Higher speed, less interference, 5 GHz 5.150 – 5.350 GHz, 5.725 – 5.850 GHz shorter range Very high-speed, minimal 6 GHz (Wi-Fi 6E) 5.925 – 7.125 GHz interference, shorter range, emerging technology EEEB1073: Topic 6: Signal Generator and 9 Oscilloscopes 6.1 Signal Generators 6.1.2 Type of Waveforms A signal generator can generate various waveforms, including sine, square, triangle, sawtooth, and arbitrary. Sine wave signals are commonly used for testing and evaluating audio systems, while square and triangle signals test digital circuits. Sawtooth and arbitrary signals test various electronic systems, as they can simulate real-world signals and conditions. EEEB1073: Topic 6: Signal Generator and 10 Oscilloscopes 6.1 Signal Generators 6.1.2 Type of Waveforms This is the standard waveform that oscillates between two levels with a standard sinusoidal shape. Sine Wave A sine wave is always useful as it provides a single frequency signal to electronic circuits. It generated by Wien Bridge Oscillator. It consists of a signal moving directly between high and low levels. A square wave with 50% duty cycle has equal duration for Square high and low level. Wave Square waves are primarily used for logic or digital circuit testing as clock signal to the circuit’s input. It is effectively the same as a square wave but having duty cycle Pulse less than 50%. This triangle-shaped signal linearly moves between a high and Triangular low point. This form of waveform is often generated using an Wave operational amplifier acting as an integrator. The triangular waveform is often used in testing amplifiers EEEB1073: Topic 6: Signal Generator and 11 Oscilloscopes 6.1 Signal Generators 6.1.2 Type of Waveforms This is a triangular waveform, but with the rise edge of the Sawtooth waveform faster or slower than the fall, making a form of shape Wave similar to a sawtooth. This waveform is similar to triangular waveform. In positive ramp waveform (ramp up), falling signal is almost instant. In negative Ramp ramp waveform (ramp down), rising signal is almost instant. This is point-to-point user defined waveform. This waveform Arbitrary describes the constantly changing voltage levels, such as Wave step/staircase waveform. EEEB1073: Topic 6: Signal Generator and 12 Oscilloscopes  Summary of Instrumentation Applications: Sine Waves: Ideal for calibration and frequency response in measurement instruments. Square Waves: Essential for timing calibration, step response, and digital circuit testing. Pulse Waves: Useful in measuring transient responses and impedance in reactive components. Triangle and Sawtooth Waves: Used for linearity testing, filter response, and calibration of scanning devices. Ramp Waves: Important in testing time-based responses and converters. Arbitrary Waveforms: Allow full customization to simulate real-world conditions and perform stress tests on specialized equipment. EEEB1073: Topic 6: Signal Generator and 13 Oscilloscopes 6.1 Signal Generators 6.1.2 Type of Waveforms Signal from generators can be modulated or unmodulated. An unmodulated signal will have fixed amplitude and frequency, like a sine wave. A modulating signal has either varying amplitude or frequency, or both. A carrier wave, which is a pure wave of constant frequency (like sine wave) is a signal that will be modulated to carry information. Modulation changes the shape of the carrier wave to somehow encode information that we were interested in carrying. Modulation is like hiding a code inside the carrier wave. If the carrier’s amplitude changed corresponding to the input signal that is been fed into it, then this is called amplitude modulation (AM). In amplitude modulation, the frequency and phase remain the same. If the carrier’s frequency changed corresponding to the input signal that is been fed into it, then this is called frequency modulation (FM). In frequency modulation amplitude and phase remain the same. EEEB1073: Topic 6: Signal Generator and Oscilloscopes 14 6.1 Signal Generators 6.1.2 Type of Waveforms Amplitude Modulation (AM) EEEB1073: Topic 6: Signal Generator and Frequency Modulation (FM) 15 Oscilloscopes  Aspect Amplitude Modulation (AM) Frequency Modulation (FM) Modulation Amplitude of carrier wave varies Frequency of carrier wave varies Technique with signal amplitude with signal frequency Bandwidth Wider bandwidth compared to FM Narrower bandwidth compared to (148.5 kHz – 283.5 kHz) AM (88 MHz – 108 MHz) Noise More susceptible to noise and Less susceptible to noise and Performance interference interference Signal Prone to amplitude distortions Generally better signal quality due Quality to resistance to amplitude variations Transmission Longer transmission range, better Limited transmission range, more Range penetration through obstacles line-of-sight dependent Applications Commonly used for broadcasting Widely used for high-fidelity audio radio signals, especially for long- transmissions, such as commercial distance transmissions radio broadcasting and music broadcasts EEEB1073: Topic 6: Signal Generator and 16 Oscilloscopes 6.1 Signal Generators 6.1.3 Types of Signal Generator Standard Signal Generator RF & Microwave Signal Generator These are the most commonly available signal RF and microwave signal generators normally generators, which can generate repeating and non- have similar features and capabilities, but are repeating analog and digital electronic signals. differentiated by frequency range. Repeating signals include sine, square, triangle, and RF signal generators typically range from a few ramp. kHz to 6 GHz, while microwave signal generators Standard signal generator produces known and cover a much wider frequency range, from less controllable voltages. The voltages are used as than 1 MHz to at least 20 GHz. power source for the measurement of gain, signal to RF (radio frequency) and microwave signal noise ratio (S/N), bandwidth, standing wave ratio generators are used for testing components, and other properties. receivers and test systems in a wide variety of These generators are extensively used in the testing telecommunication systems. EEEB1073: Topic 6: Signal Generator and of radio receivers and transmitters. Oscilloscopes 17 6.1 Signal Generators 6.1.3 Types of Signal Generator Function Generator Vector Signal Generator A waveform or function generator is a device that A vector signal generator (VSG) is a type of RF produces simple, repetitive waveforms. signal generator that can generate both amplitude Function generator generates various electrical and phase-modulated signals, also known as waveforms, such as sine, square, triangle, and vector signals. These signals have complex sawtooth, over a wide range of frequencies. modulation formats such as QPSK, QAM, etc. Function generators are crucial in electronic design VSG are essential for testing of modern data and testing in R&D, education, quality control and communications systems, everything from Wi-Fi to repair services. 4G, 5G mobile telecommunications systems and In educational settings, engineering students use many other connectivity solutions that used function generators to learn fundamentals of circuit advanced waveforms. analysis and electronic design. EEEB1073: Topic 6: Signal Generator and 18 Oscilloscopes 6.1 Signal Generators 6.1.3 Types of Signal Generator Arbitrary Waveform Generator (AWG) Pulse Generator These generators produce arbitrary waveforms within A pulse generator generates electrical signals or specified limits. AWG can produce a wide range of pulses, typically with precise timing and duration. waveforms that can be defined by the user. Unlike waveform generator which focus on While standard function generators are limited to continuous signals, pulse generators creates basic waveforms like sine and square waves, these discrete, time-bound pulses. These pulses serve as devices give you the flexibility to create both the lifeblood of digital systems, facilitating standard and intricate custom waveforms. clocking, synchronization, and data transfer. It allows you to create specific and complex signals Pulse generators play a crucial role in data that approximate those observed in real-life systems, storage technologies by producing digital pulses such as imulating a cardiac pulse in medical research used to read and write data, simulating various or generating complex modulations for conditions that the Solid-State Device (SSD) might telecommunications. EEEB1073: Topic 6: Signal Generator and encounter. 19 Oscilloscopes 6.1 Signal Generators 6.1.3 Types of Signal Generator Pitch and Audio Generator Digital Pattern Generator A pitch generator is a type of signal generator These generators produce a sequence of logic optimized for use in audio and acoustics levels or digital patterns to stimulate a circuit or applications. device. Pitch generators typically include sine waves over These patterns are vital for testing the logic and the human hearing range (20 Hz to 20 kHz). timing of digital circuits, offering a rigorous Pitch generators are typically used in conjunction evaluation of their performance under various with sound level meters, when measuring the conditions. acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers. The term synthesizer is used for a device that generates audio signals for music. EEEB1073: Topic 6: Signal Generator and 20 Oscilloscopes  Aspect Standard Signal RF & Microwave Function Vector Signal Arbitrary Pulse Generator Pitch and Audio Digital Pattern Generator Signal Generator Generator Waveform Generator Generator Generator Generator (AWG) Frequency Lower Higher Moderate Moderate to high Moderate to high Lower Audio Variable Range frequencies frequencies frequencies frequencies frequencies frequencies frequencies Output Signals Sine, square, RF/microwave Basic waveforms Complex Arbitrary Pulses Audio tones Digital triangular, etc. signals modulated waveforms waveforms signals Application Testing and RF/microwave Basic waveform Wireless Testing and Timing and Audio testing Digital logic calibration testing generation, communication simulation triggering and testing education, testing measurement laboratory Frequency High Very high Moderate High Very high High Moderate High Accuracy Amplitude High High Moderate High High High High High Accuracy Modulation Limited Comprehensive Limited Comprehensive Limited Limited Limited Comprehensive Capabilities Signal Analog Analog Analog Digital Digital Digital Analog Digital Resolution Complexity of Simple Complex Simple Complex Complex Simple Simple Complex Waveform Generation Cost Moderate High Low to moderate Moderate to high High Moderate Low to moderate High EEEB1073: Topic 6: Signal Generator and 21 Oscilloscopes  Aspect Signal Generator Function Generator Purpose Generates various types of electronic Specifically designed to generate signals for testing and measurement repetitive electronic waveforms such purposes, including sine waves, as sine, square, triangular waves, square waves, triangular waves, etc. etc., often with adjustable parameters like frequency, amplitude, and waveform shape. Signal Can generate a wide range of Primarily generates basic waveforms Complexity signals, including basic waveforms, with adjustable parameters like modulated signals, noise, and frequency, amplitude, and waveform arbitrary waveforms. shape. May lack advanced modulation capabilities. Application Widely used in various fields such as Commonly used in electronics electronics testing, laboratories, educational institutions, telecommunications, RF/microwave and engineering environments for testing, and research applications testing and calibration of electronic requiring signal generation. circuits, and for waveform demonstrations. Frequency Covers a wide frequency range, from Typically operates at moderate Range low frequencies to RF/microwave frequencies, ranging from a few Hz frequencies, depending on the to several MHz, suitable for general- model and specifications. purpose waveform generation. Modulation Offers comprehensive modulation Limited modulation capabilities, Capabilities capabilities, including AM, FM, PM, primarily focused on basic pulse modulation, and digital modulation such as AM and FM. May modulation schemes for testing lack advanced modulation features communication systems. found in signal generators. Complexity of May have complex user interfaces Generally straightforward to operate, Operation and require specialized knowledge with intuitive controls for adjusting to operate, especially for advanced waveform parameters like modulation and signal generation frequency, amplitude, and waveform techniques. shape. Cost Typically more expensive due to Usually more affordable compared advanced features, broader to signal generators, making them frequency range, and modulation accessible for educational capabilities. institutions,and EEEB1073: Topic 6: Signal Generator hobbyists, and basic testing applications. 22 Oscilloscopes  The operation of Signal Generator A signal generator is an essential electronic testing device that generates electrical signals over a wide range of frequencies. It’s commonly used in applications like testing, calibration, and troubleshooting of electronic systems, especially in communication systems. When it comes to AM (Amplitude Modulation) and FM (Frequency Modulation), signal generators play a key role in creating signals that mimic real-world broadcast signals for testing purposes. EEEB1073: Topic 6: Signal Generator and 23 Oscilloscopes  When FM ON is selected, the audio oscillator modulates the frequency of the VCO, creating a frequency-modulated (FM) signal. This is where the actual modulation occurs. Depending on the selected This oscillator generates an audio-frequency signal. mode (AM or FM), this block adjusts either the amplitude or frequency of This signal can modulate the carrier signal generated the VCO signal. by the Voltage Controlled Oscillator (VCO). After modulation, the signal passes through an amplifier to increase its strength for output. Variable attenuator is used to adjust the output signal’s amplitude before it’s sent to the output terminal. This allows for precise control over the output signal strength. When AM ON is selected, the audio oscillator modulates the amplitude of the VCO signal, creating an amplitude-modulated (AM) signal. The VCO generates a carrier signal whose frequency can be controlled. When FM is selected, the audio oscillator's output varies the VCO's frequency. If AM is selected, the VCO signal will have its amplitude modulated based on the audio oscillator’s output. EEEB1073: Topic 6: Signal Generator and 24 Oscilloscopes  AM Mode: The amplitude of the carrier signal from the VCO is modulated based on the audio oscillator's output. FM Mode: The frequency of the carrier signal from the VCO is modulated by the audio oscillator's output. EEEB1073: Topic 6: Signal Generator and 25 Oscilloscopes  Oscillator: The oscillator is the core component of a signal generator. It generates a periodic, oscillating low-frequency electronic signal that can be analog or digital. This signal is the basis for the various waveforms that the signal generator can produce. Modulator: The modulator is used to shape the waveform generated by the oscillator into the desired signal type. This can include adding modulation such as amplitude, frequency, or phase modulation to the signal. Amplifier: The amplifier increases the output signal to the desired level, which is then sent to the device under test (DUT). Output Stage: The output stage is responsible for delivering the final signal to the DUT. This stage can include features such as signal inversion, which allows the signal to be inverted or reversed. User Interface: Modern signal generators often come with an intuitive user interface that allows users to adjust various parameters such as waveform type, voltage level, frequency, and signal inversion using a series of knobs and switches. EEEB1073: Topic 6: Signal Generator and 26 Oscilloscopes  The signal / function generator can produce various types of signals, including: Sine Waves: These are continuous wave signals that are commonly used for testing and evaluating audio systems. Square Waves: These are digital signals that are used to test digital circuits. Triangle Waves: These are also digital signals used for testing digital circuits. Sawtooth Waves: These are used to test various electronic systems, as they can simulate real-world signals and conditions. Arbitrary Signals: These are complex signals that can be defined by the user and are used in applications where specific signal patterns are required. EEEB1073: Topic 6: Signal Generator and 27 Oscilloscopes  The operation of a signal generator and a function generator is similar in some aspects but differs in their specific functionalities. Both types of generators produce electrical signals with specific properties like amplitude, frequency, and waveform. However, the key differences lie in the control mechanisms for frequency generation and the types of waveforms they can produce. Similarities: Both generators use an oscillator as a core component to generate periodic signals. They both have modulators to shape the waveform and amplifiers to adjust the signal level. The output stages of both generators deliver the final signal to the device under test. They offer a user interface for adjusting parameters like waveform type, frequency, and amplitude. EEEB1073: Topic 6: Signal Generator and 28 Oscilloscopes  Differences: Frequency Control: In a signal generator, the frequency is typically controlled by varying the capacitor in the LC or RC circuit, while in a function generator, the frequency is controlled by varying the magnitude of current that drives the integrator. Waveform Generation: A function generator is specialized in producing different types of waveforms like sine, square, triangular, and sawtooth waves, whereas a signal generator can produce a wider range of signals but may not offer the same variety of waveforms as a function generator. Applications: Function generators are commonly used in RF-related operations, automotive applications, educational, medical, and industrial fields, while signal generators are more versatile and used for testing, measuring, and analyzing electronic devices and systems. EEEB1073: Topic 6: Signal Generator and 29 Oscilloscopes 6.1 Signal Generators 6.1.4 Block Diagram: AF/RF Signal Generator The signal generator, which produces the periodic signal having a frequency of Audio Frequency (AF) and Radio Frequency (RF) range is called AF and RF signal generator respectively. The range of audio frequencies is 20Hz to 20KHz while the range of radio frequencies is from 30Hz to several GHz. The block diagram consists of the upper path that produces sine wave, and the lower path that produces square wave. Wien bridge oscillator is used to produce a sine wave in the range of audio frequencies. The Wien bridge oscillator is the best of the audio frequency range. EEEB1073: Topic 6: Signal Generator and 30 Oscilloscopes  6.1 Signal Generators 6.1.4 Block Diagram: AF/RF Signal Generator The output of the Wien bridge oscillator goes to the function switch. The function switch directs the oscillator output either to the sine wave amplifier or to the square wave shaper. The upper path consists of sine wave, amplifier and attenuator that produces the desired sine wave. The lower path consists of square wave shaper, square wave amplifier, and attenuator. The square wave shaper converts the sine wave into a square wave. At the output, we get either a square or sine wave. The output is varied by means of an attenuator. EEEB1073: Topic 6: Signal Generator and 31 Oscilloscopes  This section allows the user to adjust the amplitude of the output signal before it enters In the sine wave path, the signal from the Wien Bridge Oscillator goes the amplifier, providing through a Sine Wave Amplifier to boost its strength. This oscillator generates a After amplification, the signal passes through an Attenuator to further sine wave signal at a control over the signal’s strength. adjust the amplitude, allowing fine control over the output signal’s level. specified frequency. The The signal is then sent to the Sine Output terminal, where a pure sine Wien Bridge Oscillator is wave is available for use. widely used for producing stable and low-distortion sine waves, which serve as the primary signal in this circuit. This switch allows the user to select between two types of outputs: a sine wave or a square wave. When switched to the sine wave path, the signal from the Wien Bridge Oscillator is sent directly to the Sine In the square wave path, the signal first goes to a Square Wave Shaper, Wave Amplifier. which converts the sine wave into a square wave. When switched to the The square wave then passes through a Square Wave Amplifier to square wave path, the increase its strength. signal is sent to the Finally, the amplified square wave goes through an Attenuator before Square Wave Shaper. reaching the Square Output terminal, allowing control over the output signal’s level. EEEB1073: Topic 6: Signal Generator and 32 Oscilloscopes  Sine Wave Output: The Wien Bridge Oscillator generates a sine wave, which is amplified, attenuated, and then provided as a sine output. Square Wave Output: The Wien Bridge Oscillator’s sine wave is shaped into a square wave, amplified, attenuated, and then provided as a square output. EEEB1073: Topic 6: Signal Generator and 33 Oscilloscopes 6.1 Signal Generators 6.1.4 Block Diagram: Standard Signal Generator A standard signal generator produces known and controllable voltages. The instrument is provided with a means of modulating the carrier frequency which is indicated by the dial setting on the front panel. The output signal can be Amplitude Modulated (AM) or Frequency Modulated (FM). Modulation may be done by a sine wave, square wave, triangular wave or a pulse. Standard signal generator has several key components, including an RF oscillator, wide band amplifier, external oscillator, modulation oscillator, and output attenuator. EEEB1073: Topic 6: Signal Generator and 34 Oscilloscopes 6.1 Signal Generators 6.1.4 Block Diagram: Standard Signal Generator The carrier frequency is generated by a very stable RF oscillator using an LC tank circuit, having a constant output over any frequency range. The frequency of oscillations is indicated by the frequency range control and the venire dial setting. Amplitude Modulation (AM) is provided by an internal sine wave generator or from an external source. EEEB1073: Topic 6: Signal Generator and 35 Oscilloscopes 6.1 Signal Generators 6.1.5 Signal Generator Format Signal generators are available in a variety of different formats. Bench top equipment Rack based equipment USB function generator Within Oscilloscope This equipment is This equipment is a A number of small Oscilloscopes can also contained within a box module within a rack function generators are contain a simple function that sits on the laboratory system like PXI. available as USB based generator and enable bench. This test test instruments. They them to have an onboard instrument contains the contain the core of the signal source. power supply, controls, function generator within display and of course the the module that connects output connector. to a computer via a USB EEEB1073: Topic 6: Signal Generator and connection. Oscilloscopes 36 6.1 Signal Generators 6.1.5 Signal Generator Format Software-based Oscilloscope A different approach is to use software based within a computer to provide the required waveforms and then use a digital card of the computer's audio output for the signal. Whilst very cheap, this may not have the output capability and accuracy of other types of test instrument. Also, if the output is damaged as a result of the testing and a possible misconnection, it can result in costly repairs. EEEB1073: Topic 6: Signal Generator and 37 Oscilloscopes Modern Laboratory Signal Generator EEEB1073: Topic 6: Signal Generator and 38 Oscilloscopes  The highest frequency range of 34 – 80 MHz, is passed through B1, an untuned buffer amplifier B2 and B3 are additional buffer amplifiers and A is the main amplifier. The lowest frequency range produced by the cascaded frequency divider (9 frequency dividers of 2:1 ratio are used), is the highest frequency range divided by 512, or 29, or 67 – 156 kHz. Thus, the frequency stability of the highest range is imparted to the lower frequency ranges. The use of buffer amplifiers provides a very high degree of isolation between the master oscillator and the power amplifier, and almost eliminates all the frequency effects (distortion) between the input and output circuits, caused by loading. Range switching effects are also eliminated, since the same oscillator is used on all bands. The master oscillator is tuned by a motor driven variable capacitor. EEEB1073: Topic 6: Signal Generator and 39 Oscilloscopes  For fast coarse tuning, a rocker switch is provided, which sends the indicator gliding along the slide rule scale of the main frequency dial at approximately 7% frequency changes per second. The oscillator can then be fine tuned by means of a large rotary switch (control), with each division corresponding to 0.01% of the main dial setting. The master oscillator has both automatic and manual controllers. The availability of the motor driven frequency control is employed for programmable automatic frequency control devices. Internal calibration is provided by the 1 MHz crystal oscillator. The small power consumption of the instruments makes it relatively easy to obtain excellent regulation and Q stability with very low ripple. The supply voltage of the master oscillator is regulated by a temperature compensated reference circuit. The modulation is done at the power amplifier stage. For modulation, two internally generated signals are used, that is, 400 Hz and 1 kHz. The modulation level may be adjusted up to 95% by a control device. Flip-fl ops can be used as frequency dividers to get a ratio of 2:1. EEEB1073: Topic 6: Signal Generator and 40 Oscilloscopes 6.2 Function Generators (FG) 6.2.1 Introduction to FG Recall: A function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. The output signal can be Amplitude Modulated (AM) or Frequency Modulated (FM). Modulation may be done by a sine wave, square, rectangular, orGenerator EEEB1073: Topic 6: Signal a pulse and wave. 41 Oscilloscopes 6.2 Function Generators (FG) 6.2.1 Introduction to FG Why do we need function generator? Function generators play a critical role when it comes to developing, testing, and repairing electronic equipment. For instance, they can be used to introduce an error signal into a control loop or as a signal source to test amplifiers. EEEB1073: Topic 6: Signal Generator and 42 Oscilloscopes 6.2 Function Generators (FG) 6.2.1 Introduction to FG Function Generator (FG) is basically a signal generator that produces different types of waveforms (sine wave, square wave, triangular wave, sawtooth, etc) at the output. An adjustable frequency range is provided by the FG which is in the range of some Hz to several 100KHz. FG is a versatile instrument as an extensive variety of frequencies and waveforms are produced suitable for various applications. It provides adjustment of wave shape, frequency, magnitude and offset but requires a load connected before adjustment. Some FGs can generate 2 different waveforms simultaneously at the two different terminals. Another important feature is the capability of phase locking to an external source, implying that the FG can phase lock another FG and the output of both can be displaced in phase. Two generators can be synchronized together to provide outputs at the same frequency (or at harmonics) and with a phase difference. The amplitude and phase of these outputs can also be modulated providing the capability to perform quadrature EEEB1073: Topic 6: Signal Generator and phase shift keying (QPSK) and quadrature amplitude modulation (QAM) respectively. Oscilloscopes 43 6.2 Function Generators (FG) 6.2.2 Function Generator Second Output A second output, sometimes called “sync”, “aux” or “TTL” produces a square wave with standard 0 and 5 V digital signal levels. It is used for synchronizing another device (such as an oscilloscope) to the possibly variable main output signal. EEEB1073: Topic 6: Signal Generator and 44 Oscilloscopes 6.2 Function Generators (FG) 6.2.3 Function Generator – Block Diagram There are two current sources, namely upper current source and lower current source in above block diagram. These two current sources are regulated by the frequency- controlled voltage. The Integrator gets constant current alternately from upper and lower current sources for equal amount of time repeatedly. So, the integrator will produce two types of output (positive ramp and negative ramp) for the same time repeatedly. In this way, the integrator present in above block diagram will produce a triangular wave. EEEB1073: Topic 6: Signal Generator and 45 Oscilloscopes 6.2 Function Generators (FG) 6.2.3 Function Generator – Block Diagram The triangular wave has positive slope and negative slope alternately for equal amount of time repeatedly. So, the voltage comparator multi vibrator will produce the following two types of output for equal amount of time repeatedly. The voltage comparator multi vibrator will then produce a square wave. If the amplitude of the square wave that is produced at the output of voltage comparator multi vibrator is not sufficient, then it can be amplified to the required value by using a square wave amplifier. EEEB1073: Topic 6: Signal Generator and 46 Oscilloscopes  Two Constant Current Supply The Integrator is responsible for generating a The Voltage Comparator Multivibrator monitors Sources are used to charge triangular waveform by integrating the current the voltage across the capacitor. and discharge the capacitor C supplied by the constant current sources as it When the capacitor reaches a specific voltage in the circuit. charges and discharges the capacitor. threshold, the comparator switches the current These sources provide a The triangular waveform serves as a foundational direction, causing the capacitor to discharge and constant current, causing the waveform in this function generator and is sent to then recharge, resulting in a repetitive cycle. capacitor to charge and the Output Amplifier 1 for output. This generates a square wave output, which is discharge linearly, which is sent to Output Amplifier 1. essential for generating a stable triangular waveform. The Frequency Control Network manages the frequency of the output waveforms. It can be externally adjusted to control the oscillation Output Amplifier 1 provides frequency of the function the square wave outputs. generator, affecting all output Output Amplifier 2 provides waveforms. the sine wave output. The triangular waveform can also be processed by the Resistance Diode Shaping Circuit, which modifies the shape of the triangular wave to produce a sine wave. This circuit uses resistive and diode elements to round off the sharp edges of the triangular waveform, creating a smooth sine wave. The sine wave is then amplified by Output EEEB1073: Topic 6: Signal Generator and 47 Amplifier 2 for output. Oscilloscopes Triangle Wave to Square Wave Triangle Wave to Sine Wave EEEB1073: Topic 6: Signal Generator and 48 Oscilloscopes  Square Wave: Generated by the Voltage Comparator Multivibrator and output through Output Amplifier 1. Triangular Wave: Produced by the integrator as the capacitor charges and discharges. Sine Wave: Formed by shaping the triangular wave in the Resistance Diode Shaping Circuit and output through Output Amplifier 2. EEEB1073: Topic 6: Signal Generator and 49 Oscilloscopes 6.2 Function Generators (FG) 6.2.3 Function Generator – Block Diagram The sine wave shaping circuit will produce a sine wave output from the triangular input wave. Basically, sine wave shaping circuit consists of a diode resistance network. If the amplitude of the sine wave produced at the output of sine wave shaping circuit is insufficient, then it can be amplified to the required value by using sine wave amplifier. EEEB1073: Topic 6: Signal Generator and 50 Oscilloscopes 6.2 Function Generators (FG) 6.2.4 Function Generator – Output Signal Controls In addition to a selection of the basic waveforms that are available, other output controls on the function generator may include: 1. Amplitude: This control alters the amplitude of the waveform. It is independent of the waveform type. 2. Frequency: This control alters the basic frequency of the waveform. It is independent of the waveform type. 3. Waveform type : This enables the different basic waveform types to be selected: Sine wave Square wave Triangular wave 4. DC offset: This alters the average voltage of a signal relative to 0V or ground. Means that a DC offset shifts the entire waveform vertically, changing its average (or mean) voltage. In practical terms, this offset makes the signal sit higher or lower than 0V (ground) on average, rather than oscillating symmetrically around 0V. 5. Duty cycle: This control on the function generator changes the ratio of high voltage to low voltage time in a square wave signal, i.e. changing the waveform from a square wave with a 1:1 duty cycle to a pulse waveform, or a triangular EEEB1073: waveformTopicwith equal 6: Signal riseand Generator and fall times to a sawtooth. 51 Oscilloscopes EEEB1073: Topic 6: Signal Generator and 52 Oscilloscopes  Application Purpose of DC Offset Voltage Shifts an AC signal into a positive range for circuits that can only handle positive Signal Conditioning voltages, avoiding signal clipping. Sets the operating point (bias) for transistors, keeping the amplified signal Amplifiers and Biasing centered within the acceptable range of subsequent stages. Maintains the signal above a threshold to avoid distortion and ensure signal Communication Systems integrity across different stages, such as in RF transmitters. Adds a DC component to waveforms for testing circuits that need a baseline Waveform Generation voltage or to simulate real-world signals with slight offsets. Shifts sensor signals to fit within the desired measurement range, allowing for Measuring Systems accurate readings in analog or digital systems. EEEB1073: Topic 6: Signal Generator and Oscilloscopes 53 EEEB1073: Topic 6: Signal Generator and 54 Oscilloscopes EEEB1073: Topic 6: Signal Generator and 55 Oscilloscopes EEEB1073: Topic 6: Signal Generator and 56 Oscilloscopes 6.2 Function Generators (FG) 6.2.5 Function Generator – Front Panel EEEB1073: Topic 6: Signal Generator and 57 Oscilloscopes 6.2 Function Generators (FG) 6.2.6 Function Generator – Specifications and Performance Parameters 1. Waveforms: Sine wave distortion and flatness – distortion refers to any deviation from an ideal sine wave shape while flatness refers Example of sine wave distortion to the stability of the signal amplitude. Maximum sine wave distortion is about 1%. Triangular wave linearity – maximum deviation from an ideal triangle wave. Typical linearity is 99% between 10% and Linearity of triangle wave 90% of the waveform amplitude. Square wave rise and fall time – typically rise and fall time is less than 100ns between 10% and 90% of the waveform amplitude. EEEB1073: Topic 6: Signal Generator and 58 Rise time and fall time of square wave Oscilloscopes 6.2 Function Generators (FG) 6.2.6 Function Generator – Specifications and Performance Parameters 2. DC Offset: DC offset enables the base 3. Frequency range: The lower frequency voltage level of the signal to be varied limits tend to be below 1 Hz, often 0.1 or over a given range. It may be variable 0.2 Hz. The upper frequency limit vary over a range +5V to -5V for example. considerably from around 1 MHz up to 20 MHz or more. 4. Amplitude range: The amplitude of all function outputs is adjustable, normally up to 20Vpp. 5. Output impedance: Most function generators are designed with a 50 output impedance. EEEB1073: Topic 6: Signal Generator and 59 Oscilloscopes 6.2 Function Generators (FG) 6.2.6 Function Generator – Specifications and Performance Parameters (Examples) EEEB1073: Topic 6: Signal Generator and 60 Oscilloscopes 6.2 Function Generators (FG) 6.2.7 Function Generator - Precautionary Measures to be taken in a Function Generator Application 1. The amplitude and frequency of the output of the signal generator should be made stable and well known. 2. There should be provision for controlling the amplitude of signal generator output from very small to relatively large values. 3. The output signal of generator should not contain any distortion and thus, it should possess very low harmonic contents. 4. Also, the output of the signal generator should be less spurious. EEEB1073: Topic 6: Signal Generator and 61 Oscilloscopes 6.3 Oscilloscopes 6.3.1 Introduction What is oscilloscope? Oscilloscope is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing information on electrical signals for debugging, analysis, or characterization. The displayed waveform can then be analyzed for properties such as amplitude, frequency, rise time, time interval, distortion, and others. EEEB1073: Topic 6: Signal Generator and 62 Oscilloscopes 6.3 Oscilloscopes 6.3.2 Oscilloscope Working Operation An oscilloscope can be used to measure voltage by measuring the voltage drop across a resistor, and in the process draws a small current. The voltage drop is amplified and used to deflect an electron beam in either the X (horizontal) or Y (vertical) axis using an electric field. The electron beam creates a bright dot on the face of the Cathode Ray Tube (CRT) where it hits the phosphorous. The deflection, due to an applied voltage, can be measured with the aid of the calibrated lines on the graticule. EEEB1073: Topic 6: Signal Generator and 63 Oscilloscopes The oscilloscope has two main deflection systems: X-axis (horizontal) and Y-axis (vertical). Deflection Plates: These plates generate an electric field that deflects the electron beam. The X-axis deflection plates control horizontal movement, while the Y-axis deflection plates control vertical movement. Amplifiers for both the X and Y axes amplify the input signals to control the deflection of the electron beam in the respective directions. Inverters: The inverters are used to reverse the polarity of the signals applied to the deflection plates, allowing for control over the direction of deflection. By applying an inverted signal to these plates, the direction of the beam’s deflection can be reversed. For instance, a positive signal on the Y-axis plate might push the beam up, while an inverted (negative) version of the same signal would EEEB1073: Topic 6: Signal Generator and pull the beam down. 64 Oscilloscopes The display screen shows the position of the Center Graticule Line: The center line acts as a electron beam as it is deflected by the X and Y axis reference point, typically representing zero or the signals. baseline for the signal. The rise time measurement marks on an oscilloscope graticule are used to measure the time it takes for a signal to transition from a low to a high value, specifically from 10% to 90% of its full amplitude. Rise time is a crucial parameter, especially in digital and high-speed applications, as it helps evaluate how quickly a signal can respond to changes. Graticule Lines: These lines provide a reference Rise Time Measurement Marks: These are grid on the screen, with both major and minor specific markings that help measure the rise time divisions. This grid helps in measuring amplitude, of a signal, which is the time it takes for the signal frequency, and time intervals of the waveform to change from a low to a high value. EEEB1073: Topic 6: Signal Generator and 65 displayed. Oscilloscopes  The overall operation involves feeding signals into the X and Y amplifiers, which adjust the electron beam's position on the screen by controlling its deflection through the plates. The graticule on the display screen then allows the user to measure and analyze the waveform's properties, such as voltage levels, time intervals, and rise times. EEEB1073: Topic 6: Signal Generator and 66 Oscilloscopes 6.3 Oscilloscopes The deflection of the oscilloscope beam is proportional to the input voltage (after ac 6.3.2 Oscilloscope Working or dc coupling). The amount of deflection Operation (Volts/Division) depends upon the setting of the AMPL/DIV control for that channel. The input signal can be ac or dc coupled. AC coupling involves adding a series capacitor. This has the effect of blocking (removing) the dc bias and low frequency components of a signal. DC coupling does not have this problem and therefore allows you to measure voltages right down to 0 Hz. AC coupling is useful when you are trying to measure a small ac voltage that is “on- top” of a large dc voltage. A typical example is trying to measure the noise of a EEEB1073: Topic 6: Signal Generator and dc power supply. Oscilloscopes 67 The input signal can be coupled to the oscilloscope via AC, DC, or ground (0) settings, controlled by a switch. AC Coupling: Filters out the DC component of the signal, allowing only the AC component to pass through. This is useful for observing variations in signals that ride on top of a DC offset. DC Coupling: Allows both AC and DC components of the signal to pass through, showing the complete waveform including any DC offset. Ground (0): Disconnects the input signal, allowing the baseline position to be calibrated or checked without any input signal interference. Signal Processing Stages: Voltage Divider: Adjusts the signal amplitude based on the amplitude- per-division setting, allowing users to scale the signal to fit appropriately on the screen. Invert: An inversion option that reverses the polarity of the input signal, displaying it upside down. This is useful for comparing signals or viewing inverted representations. Position Amplifier: Controls the vertical or horizontal position of the signal on the screen, allowing users to center the waveform as needed. EEEB1073: Topic 6: Signal Generator and 68 Oscilloscopes  Signal (Original): Shows a waveform with both AC and DC components. DC Coupling: Displays the entire signal, including both AC variations and the DC offset, allowing users to see the true voltage levels. AC Coupling: Filters out the DC component, showing only the AC variations centered around zero, which is useful for analyzing the waveform's A DC offset refers to a constant voltage added to an AC fluctuations without considering the (alternating current) signal, shifting the entire waveform up or down relative to the zero-voltage baseline. In other words, it’s a DC level. DC component that causes the signal to be displaced vertically on an oscilloscope or in any circuit. EEEB1073: Topic 6: Signal Generator and 69 Oscilloscopes  The oscilloscope processes incoming signals through coupling options (AC, DC, or ground) and adjusts the waveform’s amplitude, polarity, and position before displaying it on the screen. This setup enables users to analyze signal characteristics effectively, choosing the coupling method based on the measurement requirements. Mode When to Use To observe the full waveform, including both AC and DC components, such as DC Coupling in power supply or signal with a steady DC level. To focus only on the AC component by removing the DC offset, useful for AC Coupling signals with small fluctuations superimposed on large DC voltages. To establish a zero reference or check the oscilloscope baseline, helpful for Ground calibration or baseline adjustments. EEEB1073: Topic 6: Signal Generator and 70 Oscilloscopes 6.3 Oscilloscopes 6.3.2 Oscilloscope Working Operation The main function of an oscilloscope is to show voltage vs time. This is done by applying a ramp (or sawtooth) waveform into the X-axis amplifier. During the rising edge of the ramp, the electron beam scans across the screen. When the voltage drops back to 0V, the beam is turned off and quickly goes back to its starting point. This is signified by a thick line when the beam is on and a thin one when it is off (blanked). EEEB1073: Topic 6: Signal Generator and 71 Oscilloscopes  The oscilloscope uses a pair of deflection plates to control the movement of the electron beam in both the Y-axis (vertical) and X-axis (horizontal). Y-Axis (Vertical) Input: The input waveform signal (e.g., a sine wave) is applied to the Y-axis amplifier, which drives the vertical deflection plates. This causes the electron beam to move up and down based on the amplitude of the input signal. X-Axis (Horizontal) Input: A ramp waveform (or "sawtooth" signal) is applied to the X-axis amplifier, creating a consistent horizontal sweep. This signal, known as the time base, ensures the beam moves horizontally at a constant rate, enabling the display of waveforms over time. EEEB1073: Topic 6: Signal Generator and 72 Oscilloscopes Time Base Generator: The time base generator produces a Deflection Plates: The Y-axis deflection plates adjust the ramp waveform, which controls the horizontal movement of vertical position of the beam in response to the input the beam, synchronizing it with the frequency of the input waveform. The X-axis deflection plates, driven by the ramp signal. waveform, move the beam horizontally at a steady rate. The Y-axis displays the amplitude of the input signal, while the X-axis represents time, controlled by the ramp waveform from the time base generator. By adjusting the time base settings (e.g., time per division), users can change the horizontal scale, allowing for a detailed view of fast or slow signals. The result is a waveform display that shows variations in the input signal over time, providing insights into signal properties like frequency, amplitude, and phase. Fluorescent Screen: When the electron beam strikes the Electron Gun: The electron gun emits a beam of electrons screen, it creates a visible trace. The combined vertical (Y-axis) directed toward the fluorescent screen. The beam passes and horizontal (X-axis) deflections produce a two-dimensional through deflection plates that adjust its trajectory according to representation of the waveform on the screen, showing the the input signals. input signal’s amplitude over time. EEEB1073: Topic 6: Signal Generator and 73 Oscilloscopes  The oscilloscope uses deflection plates driven by an input waveform and a time base signal to control the electron beam’s movement on a fluorescent screen. This process enables the visual representation of waveforms, allowing users to analyze signal characteristics in a time-based format. EEEB1073: Topic 6: Signal Generator and 74 Oscilloscopes Block diagram of a cathode-ray oscilloscope: EEEB1073: Topic 6: Signal Generator and 75 Oscilloscopes EEEB1073: Topic 6: Signal Generator and 76 Oscilloscopes EEEB1073: Topic 6: Signal Generator and Oscilloscopes 77 6.3 Oscilloscopes 6.3.2 Oscilloscope Working Operation To obtain a stable picture on the CRT screen, the ramp waveform has to be in phase with the signal that you want to observe. This is done with a triggering circuit that allows the oscilloscope to draw repeatedly the same waveform over and over by identifying the same point on a repetitive waveform. The triggering circuit allows you to select a voltage (an analog value) and an edge or slope (positive or negative) for the triggering circuit to compare to the input waveform. When the two are equal, the circuit puts out a pulse. This pulse triggers the ramp waveform generator to do one cycle of its rising and falling edges. Once the ramp has started a cycle of increasing voltage, it can not be retriggered until it has EEEB1073: Topic 6: Signal Generator and 78 completed the full ramp and returned to 0V. Oscilloscopes 6.3 Oscilloscopes 6.3.2 Oscilloscope Working Operation Not only do you have control over the starting point of the ramp, but the amount of time that the ramp takes to reach its maximum voltage can be adjusted with the time base control. In essence, you have a “window”. You can move the window to any point on a waveform with the triggering circuit and you can change the size of the window with the timebase. The time-base control allows you to set the time/division that the beams takes to scan across the screen. EEEB1073: Topic 6: Signal Generator and 79 Oscilloscopes EEEB1073: Topic 6: Signal Generator and 80 Oscilloscopes Vtrigger: This is the set trigger voltage level at which the oscilloscope initiates a sweep. The oscilloscope monitors the input signal for this specific voltage level. Trigger Pulse: When the input signal reaches the trigger level, a trigger pulse is generated, which activates the time base ramp. Time Base Ramp: The time base ramp is the signal responsible for the This process is repeated for each cycle of the waveform, horizontal sweep of the electron ensuring that the waveform starts from the same point on each beam across the screen. Each time the sweep. This synchronization keeps the waveform stable and trigger pulse is generated, it resets stationary on the screen. the time base ramp, starting a new sweep from left to right. EEEB1073: Topic 6: Signal Generator and 81 Oscilloscopes Triggering on a Negative Slope: The oscilloscope can be set to trigger on different slopes of the input signal, such as a positive (rising) or negative (falling) slope. In this example, the oscilloscope is set to trigger on the negative slope, meaning it initiates the sweep when the waveform crosses the trigger voltage VtV_tVt on its way down. Display on the Screen: Once the trigger is activated, the time base begins the sweep, displaying the waveform on the oscilloscope screen. The consistent trigger point ensures that each sweep starts from the same point in the waveform, making it appear stable and easy to analyze. Time Based Ramp EEEB1073: Topic 6: Signal Generator and 82 Oscilloscopes  Trigger Level: The user can adjust this level to choose the voltage at which the oscilloscope triggers. Setting the trigger level at an appropriate point in the waveform is crucial for a clear, stationary display. Slope Selection: By selecting either the positive or negative slope, the user determines whether the oscilloscope should start the sweep as the waveform rises or falls through the trigger level. Stable Display: With proper triggering, the oscilloscope provides a stable and repeatable display of the waveform, which is essential for analyzing periodic signals like sine waves, square waves, and other recurring patterns. The oscilloscope’s triggering mechanism synchronizes the waveform with the horizontal sweep, ensuring a stable display by initiating the sweep at the same point in the waveform each time. This allows for accurate measurement and analysis of waveform properties. EEEB1073: Topic 6: Signal Generator and 83 Oscilloscopes  Signal Input to Vertical Plates (A): The input signal (e.g., a sine wave) is applied to the vertical deflection plates. This controls the Y-axis movement of the electron beam on the screen. As the signal varies over time (from point a to b to c and d), it causes the beam to move up and down, corresponding to the amplitude of the waveform. The maximum and minimum points of the signal correspond to the highest and lowest vertical deflections on the screen. EEEB1073: Topic 6: Signal Generator and 84 Oscilloscopes  Resultant Display (C): The combination of the vertical and horizontal deflections results in a two-dimensional display of the input waveform on the oscilloscope screen. Points a, b, c, and d on the input waveform are mapped to corresponding points on the screen, creating a stationary image of the waveform. By controlling the time base (horizontal sweep) and the vertical deflection (signal amplitude), the oscilloscope provides an accurate visual representation of the waveform over time. Ramp Signal Input to Horizontal Plates (B): A ramp waveform (also known as a time base signal) is applied to the horizontal deflection plates. This ramp signal provides a consistent X-axis sweep for the beam, moving it horizontally across the screen from left to right. The ramp signal is synchronized with the input signal, ensuring a steady horizontal sweep rate that matches the frequency of the waveform. As the ramp signal progresses from 0 to d, it moves the beam horizontally, allowing the waveform to be displayed across the screen. EEEB1073: Topic 6: Signal Generator and 85 Oscilloscopes The oscilloscope displays waveforms by: Applying the input signal to the vertical plates to control the Y- axis movement based on the signal’s amplitude. Using a ramp waveform on the horizontal plates to move the electron beam from left to right across the screen. The synchronization of these signals allows the oscilloscope to display a stable and accurate representation of the input waveform, which can be analyzed for its amplitude, frequency, and other properties. EEEB1073: Topic 6: Signal Generator and 86 Oscilloscopes 6.3 Oscilloscopes 6.3.3 Two-channel Operation The two channels on a dual channel oscilloscope can be used to observe and compare two different signals. For example, if you want to compare the input and output of an amplifier. The individual channels are sometimes labelled as '1' and '2' or as 'A' and 'B'. Since there is only one electron beam, you have to share its drawing time between both waveforms. This may be accomplished using either the chop mode or alternate mode. EEEB1073: Topic 6: Signal Generator and 87 Oscilloscopes 6.3 Oscilloscopes 6.3.3 Two-channel Operation When in the chop mode, the oscilloscope displays a little bit of channel A, then a little bit of B, then A, then B.... during a single sweep of the electron beam. Here, the electronic switch undergoes free running at a very high frequency of about 100 kHz to 500 kHz, independent of the frequency of sweep generator. The small segments of the two channels get connected to the amplifier in a continuous manner. Then the separately chopped segments will be merged and recombine to form originally applied channel A and B waveform at the screen of CRT. EEEB1073: Topic 6: Signal Generator and 88 Oscilloscopes 6.3 Oscilloscopes 6.3.3 Two-channel Operation In the alternate mode, the oscilloscope will sweep the electron beam twice across the screen. The first time it will draw the signal from channel A and the next time from channel B. This alternation or switching between the channels A and B takes place at the beginning of each upcoming sweep of the sweep generator. Thus, the two waveforms that you see are from different points in time. This method cannot be used for the representation of the low-frequency signal. When combined with alternate displaying, you can stably display two waveforms of any frequency by alternately showing each channel and triggering on the channel that is being drawn. EEEB1073: Topic 6: Signal Generator and 89 Oscilloscopes Delay Lines: Delay lines (labeled Delay Line A and Delay Line Electronic Switch and Vertical Amplifier: An electronic B) are used to synchronize the signals, allowing sufficient time switch selects which channel (A or B) to display, sending the for processing before they are displayed. This prevents phase signal to the vertical amplifier. The switch can alternate shifts and maintains signal integrity. between channels, enabling both signals to be displayed on the screen in a single trace or alternating format. Channel A and Channel B: Each input channel has its own pre- amplifier and attenuator to amplify or reduce the signal as needed. Trigger Circuit and Sweep Generator: The trigger circuit X-Y Mode: The oscilloscope can operate in X-Y mode to plot selects the trigger source (Channel A, Channel B, or an external one signal against the other, with Channel A as the X-axis and trigger) and synchronizes the horizontal sweep (time base) with Channel B as the Y-axis. This is useful for Lissajous patterns and the selected signal, stabilizing the display. phase comparison. EEEB1073: Topic 6: Signal Generator and 90 Oscilloscopes  Alternate Display: In this mode, the oscilloscope alternates between displaying Channel A and Channel B, showing both waveforms on the screen separately but simultaneously. Each signal is triggered individually, allowing distinct, non- overlapping waveforms for each channel. Alternate Trigger and Display: This mode alternates the display of the signals, but each channel is triggered separately, ensuring synchronization with the signal's frequency. This results in both waveforms being displayed on the screen with shared trigger points, making it easier to compare the waveforms and analyze their phase relationship. EEEB1073: Topic 6: Signal Generator and 91 Oscilloscopes  Two-Channel Display: By using an electronic switch, the oscilloscope can display two channels in either alternating mode or overlay mode, depending on the analysis needs. Trigger Synchronization: The trigger circuit stabilizes each waveform, ensuring that each channel’s signal is displayed starting from a consistent point. X-Y Mode: When using X-Y mode, the oscilloscope plots the two signals against each other rather than over time, which is particularly useful for comparing phase differences or visualizing frequency relationships. In summary, a two-channel oscilloscope allows users to display and analyze two separate waveforms, either by alternating between them or by overlaying them with synchronized triggering. This functionality is essential for comparing signals, such as in differential measurements, phase analysis, or dual- trace monitoring. EEEB1073: Topic 6: Signal Generator and 92 Oscilloscopes  Explanation of Each Waveform 1.Horizontal Sweep Voltage (i): 1. This is the time base signal that creates a horizontal sweep across the oscilloscope screen. 2. The waveform has a sawtooth shape with a "hold-off" period followed by a rapid "flyback" to the start position. During the flyback period, the beam returns to the left side of the screen, preparing for the next sweep. 3. This sweeping action is synchronized with the channel switching to ensure both channels are displayed alternately in a stable manner. 2.Channel A Voltage (ii): 1. The Channel A signal is displayed only when the oscilloscope’s switching mechanism directs the beam to show Channel A. 2. During this period, Channel A’s signal is visible on the screen, and Channel B is held off. 3. This alternation continues, with Channel A being displayed during one sweep cycle and Channel B in the next. 3.Channel B Voltage (iii): 1. The Channel B signal is displayed when the switching mechanism selects Channel B. 2. Sim