Digital and Analogue Systems

Digital vs. Analogue Systems

• A digital system comprises devices that process logical information or physical quantities in digital form, using quantities with discrete values.
• Digital systems are usually electronic but can be mechanical, magnetic, or pneumatic.
• Familiar digital systems include digital computers, calculators, audio/video equipment, and telephone systems.
• An analogue system consists of devices manipulating physical quantities represented in analogue form, where quantities vary over a continuous range.
• The amplitude of a radio receiver's output signal to the speaker exemplifies an analogue system, having values between zero and its maximum with infinite points in between.
• Examples of analogue systems are audio amplifiers, magnetic tape recording equipment, and light dimmer switches

Microelectronics

• Discrete components are individual packaged components like semiconductors, resistors, and capacitors.
• Integrated circuits (ICs) are complex devices with complete circuits in a single component.
• Microelectronics is the term for using these devices to miniaturize electronic equipment.

Introduction to Microelectronics

• The first integrated circuit was produced around 1960 by Fairchild Semiconductor.
• It included a bi-stable RS (Reset/Set) Flip-Flop with four NPN bipolar transistors and two resistors on a silicon chip.
• The maximum operating clock speed was 1 MHz, with a delay of 50 nanoseconds.

Integrated Circuits

• An integrated circuit integrates active components (transistors, diodes) and passive components (resistors, capacitors, inductors) of a complete electronic circuit on a semiconductor crystal or insulator chip.
• Integrated circuits have largely replaced individual electronic components as building blocks.
• Chips can contain transistors, resistors, and capacitors that interconnect, replacing single parts with integrated complex circuits.
• These chips, often mounted on a printed circuit board, comprise multistage amplifiers, logic and linear circuits, and operational amplifiers.

Advantages of Integrated Circuits

• Integrated circuits offer:
• Drastic reduction in size and weight.
• Increased reliability.
• Lower costs.
• Possible improved circuit performance.
• Lower power consumption.
• Reduced heating.
• Integrated circuits are composed of closely associated parts, making repairs difficult, thus, requiring replacement as a single component.
• They are applicable in aviation, airborne equipment, missile systems, computers, spacecraft, and portable equipment.
• Integrated circuits come in tiny packages that protect and dissipate heat, containing single or multiple stages, often with hundreds of components.

Logic Integrated Circuits

• A digital logic circuit, a type of nonlinear circuit, deals with discrete representations of data (numbers) instead of analogue data (voltage levels).
• An analogue-to-digital converter (ADC) converts analogue voltage to a number, processing it through logic circuitry.
• Logic circuits use logic gates to perform logic on discrete inputs for computer devices, from washing machines to flight control systems.
• Complex logic actions are divided into simple actions: AND, OR, and NOT, forming the basis of complex computing.
• A logic integrated circuit is an electronic device with entire logic circuit(s) inside, ranging in complexity from small circuits to millions of logic circuits.
• Complex integrated circuits, known as microprocessors, act as central processing units (CPUs) in computers.

The AND Function

• The AND function is shown by the intersection of 2 or more circles which represent physical conditions.
• All inputs must be present for fire to occur; if any parameter is missing, there is no fire.
• Electrically, the AND function is represented by series switches; power outputs only when all switches are closed.

The OR Function

• The OR function is represented by the area of 2 or more circles representing physical conditions, where anything within the area of the circles will illuminate a lamp.
• The OR function is represented electrically by parallel switches; any switch closed will power the light.

The NOT Function

• The NOT gate output is opposite to the input.
• Closing the switch extinguishes the lamp, and opening the switch illuminates it.

Linear Integrated Circuits

• A linear circuit is an analogue circuit, which has continuous values within a range, in contrast to a digital function, which has discrete values or steps.
• Linear circuits include:
• Operational amplifiers.
• Voltage regulators.
• Communication circuits.
• Interface circuits.
• A linear integrated circuit is a device containing an entire linear circuit within.
• Specific ICs perform specific circuit functionalities.

Operational Amplifiers

• The operational amplifier (op-amp) has two inputs: inverting (-) and non-inverting (+), and one output terminal.
• Op-amps commonly operate with two DC supply voltages, one positive and one negative, usually omitted for simplicity in schematics.
• A common operational amplifier is the 741 op-amp IC, an 8-pin integrated circuit.

The Ideal Op-Amp

• The ideal op-amp characteristics include:
• Infinite voltage gain and bandwidth.
• Infinite input impedance (open).
• Zero output impedance.
• The input voltage (Vin) appears between the two input terminals, and the output voltage as indicated by the internal voltage source symbol.

The Practical Op-Amp

• Practical op-amps have limitations, including voltage and current limits.
• The peak-to-peak output voltage is less than supply voltages, and output current is limited by power dissipation and component ratings.
• Practical op-amp characteristics:
• High voltage gain (20,000 to 200,000).
• High input impedance (approximately 2ΜΩ).
• Low output impedance (75Ω).
• Wide bandwidth (100,000Hz to 1,000,000Hz).

Operational Amplifier Operation

• An op-amp comprises a differential amplifier, a voltage amplifier, and a push-pull amplifier.
• A differential amplifier, the input stage, amplifies the difference voltage between the two inputs.
• Op-amps can have gains from 50,000 to 200,000 (up to 350,000 for some), amplifying small input signals.
• The op-amp's output is driven to saturation, close to the supply voltage, when operating in open-loop without feedback.
• Comparators use open-loop operation.
• Connecting the negative input to a reference voltage (e.g., 0V) and applying an input to the positive input, the output will be limited by power supply voltages.
• With an input above the reference, the output nears the maximum positive supply voltage, and below, the output nears the maximum negative supply voltage.

Op-Amp Negative Feedback

• Amplification is controlled using negative feedback to keep it within the circuit's capability in the inverting amplifier.
• Part of the output voltage is fed back to the negative input.
• Feeding part of the input into the positive input is positive feedback or feed-forward.

Op-Amp Voltage Follower

• Analogue applications use Op-Amps with negative feedback.
• Voltage Follower Op-Amps do not amplify, operating at Unity Gain (gain of 1).
• The feedback resistor equals the input resistor, inverting the same output value.
• The value of R is kept high to limit current and reduce wasted energy.
• Unity Gain arrangements, called Voltage Followers, track the input voltage at the output.
• Sometimes you want an output that is Inverting, and sometimes you want one that is Non-Inverting.
• Non-inverting voltage follower: the output voltage adjusts the reference voltage until it equals the input voltage.
• It is thought to have 100% negative feedback, limiting the output voltage to the input voltage.