Electronic Communications Systems Introduction PDF

Introduction Electronic Communications Systems Engr. Marco Ceferino C. Guerrero ECE6 – Communications 1 TF 7:00-10:00 am EL – 11 Objectives Define the fundamental purpose of an electronic communication system. Describe analog and digital signals. Define and descri...

Introduction Electronic Communications Systems Engr. Marco Ceferino C. Guerrero ECE6 – Communications 1 TF 7:00-10:00 am EL – 11 Objectives Define the fundamental purpose of an electronic communication system. Describe analog and digital signals. Define and describe the basic power units in dB and dBm. Explain the terms modulation and demodulation. Describe the electromagnetic spectrum. Define bandwidth, information capacity, and electrical noise. Explain signal-to-noise ratio and noise figure and their significance in electronic communication systems. What is electronic communications? INTRODUCTION What is electronic communications? It is the transmission, reception, and processing of information between two or more locations using electronic circuits. Analog Signals Are time-varying voltages or currents that are continuously changing such as sine and cosine waves. Digital Signals Are voltages or currents that change in discrete steps or levels. COMMUNICATIONS HISTORY HAND GESTURES & FACIAL EXPRESSIONS VERBAL GRUNTS & MOANS SMOKE SIGNALS & DRUMS 1837 – SAMUEL FINLEY BREESE MORSE 1876 – 'Mr. Watson, Come Here...' 1894 – Marchese Guglielmo Marconi 1906 – Lee DeForest and his Audion Tube 1920 – First Commercial Radio Broadcast 1931 – Major Edwin Howard Armstrong 1935 – First Commercial FM Broadcast  High Frequency BASIC ELEMENTS OF Oscillator ANALOG COMMUNICATION SYSTEM Information Frequency Up- Source and Input Modulator Power Amplifier Converter Transducer High Frequency Communication Local Oscillator Channel Output Frequency Demodulator Amplifier Transducer Down-Converter Analog Signals Are time-varying voltages or currents that are continuously changing such as sine and cosine waves. DIGITAL SIGNALS Are voltages or currents that change in discrete steps or levels. POWER MEASUREMENTS dB, dBm, and Bel Decibel ( dB ) Is a logarithmic unit that can be used to measure ratio. It is used as transmission measuring unit to express relative gains and losses of electronic devices and circuits and for describing relationships between signal and noise. dBm Is a unit of measurement used to indicate the ratio of a power level with respect to a fixed reference level (1mW). Bel One-tenth of a decibel. Decibel dB, dBm, and Bel Decibel (dB) The decibel is a logarithmic unit that can be used to measure ratios of virtually anything. Its practical value arises from its logarithmic nature, which permits enormous range of power ratios to be expressed in terms of decibels without excessively large or extremely small numbers. Decibel (dB) The dB is a transmission-measuring unit used to express relative gains and losses of electronic devices and circuits for describing relationships between signal and noise. Decibel ( dB ) 𝑷𝟏 𝒅𝑩 = 𝟏𝟎𝒍𝒐𝒈 𝟏𝟎 𝑷𝟐 Where: P1 = power level 1 (watts) P2 = power level 2 (watts) Decibel ( dB ) 𝑷𝒐𝒖𝒕 𝑨𝒑(𝒅𝑩) = 𝟏𝟎𝒍𝒐𝒈 𝟏𝟎 𝑷𝒊𝒏 Where: Ap(db) = power gain (dB) Pout = output power level (watts) Pin = input power level (watts) 𝑃𝑜𝑢𝑡 = absolute power gain (unitless) 𝑃𝑖𝑛  Problem 1 Convert the absolute power ratio of 200 to a power gain in dB. Problem 2 Convert a power gain Ap = 46 dB to an absolute power ratio. Properties of Logarithm (Review) log mn = log m + log n log (m/n) = log m - log n log mn = n log m log 1 = 0 irrespective of the base ***Please take note of the pattern. Absolute Ratio log10(ratio) 10log10(ratio) 1 0 0 1.26 0.1 1 2 0.301 3 4 0.602 6 8 0.903 9 10 1 10 100 2 20 1000 3 30 10000 4 40 100000 5 50  Absolute Ratio log10(ratio) 10log10(ratio) 0.00001 -5 -50 0.0001 -4 -40 0.001 -3 -30 0.01 -2 -20 0.1 -1 -10 0.5 -0.301 -3 0.25 -0.602 -6 0.79 -0.1 -1 ***Please take note of the pattern. Decibel ( dB ) in terms of a Voltage Ratio 𝑬𝒐𝟐/𝑹𝒐 𝑨𝒗(𝒅𝑩) = 𝟏𝟎𝒍𝒐𝒈 𝟏𝟎 𝑬𝒊𝟐/𝑹𝒊 Where: Av(db) = power gain (dB) Eo = output voltage (volts) Ei = input voltage (volts) Ro = output resistance (ohms) Ri = input resistance (ohms) If Ro = Ri, 𝑬𝒐 𝑨𝒗(𝒅𝑩) = 𝟐𝟎𝒍𝒐𝒈 𝟏𝟎 𝑬𝒊 Where: Av(db) = power gain (dB) This equation can Eo = output voltage (volts) be used regardless Ei = input voltage (volts) of whether the Ro = output resistance (ohms) output and input Ri = input resistance (ohms) resistance are equal  Problem 3 You're working on a Specs: communication system that Cable type: Coaxial cable with a transmits data over a 50-meter characteristic impedance of 50 ohms coaxial cable. The signal source Cable length: 50 meters generates a voltage of 1 V at the Cable attenuation: 3 dB/m (decibels per meter) transmitter end. Determine the Voltage at sending end: 1 Volt received signal strength in volts at the other end of the cable, considering there is signal attenuation along the cable. dBm dB, dBm, and Bel dBm It is a unit of measurement used to indicate the ratio of a power level with respect to a fixed reference level. With this, the reference level is 1mW. dBm 1mW was chosen for the reference because it equals the average power produced by a telephone transmitter. This 1mW average power was probably taken between 1920s and 1940s. Also, 1mW was a common power level for many transmitters and receivers, historically. dBm 𝑷 𝒅𝑩𝒎 = 𝟏𝟎𝒍𝒐𝒈 𝟏𝟎 𝟎. 𝟎𝟎𝟏 𝑾 Where: 0.001 W is the reference power of 1mW P is any power in watts  Problem 1 Convert a power level of 200 mW to dBm. Problem 2 Convert a power level of 33 dBm to an absolute power.  dBW – the reference signal is 1W dBkW – the reference signal is 1kW dBu – the reference signal is 1uW Bel dB, dBm, and Bel Bel Alexander Graham Bel Bel is one-tenth of a decibel. Bel 𝑷𝒐𝒖𝒕 𝑩𝒆𝒍 = 𝒍𝒐𝒈 𝟏𝟎 𝑷𝒊𝒏 Where: Pout = output power level (watts) Pin = input power level (watts) 𝑃𝑜𝑢𝑡 = absolute power gain (unitless) 𝑃𝑖𝑛 Examples Power Levels, Gains, and Losses  Example 1 A three-stage system Determine: comprised of two amplifiers 1. Input power in dBm and one filter. The input power Pin = 0.1mW. The 2. Output power (Pout) in watts absolute gains are Ap1 = 100, and dBm Ap2 = 40, and Ap3 = 0.25. 3. dB gain of each of the three stages 4. Overall gain in dB 𝑃𝑜𝑢𝑡 𝑑𝐵𝑚 − 𝑃𝑖𝑛 𝑑𝐵𝑚 = 𝐴𝑝𝑡𝑜𝑡𝑎𝑙 𝑑𝐵 𝑃𝑜𝑢𝑡 𝑑𝐵𝑚 = 𝑃𝑖𝑛 𝑑𝐵𝑚 + 𝐴𝑝𝑡𝑜𝑡𝑎𝑙 𝑑𝐵  Example 2 For a three-stage system with an input power Pin = -20 dBm and power gains of the three stages as Ap1 = 13 dB, Ap2 = 16dB, and Ap3 = -6 dB, determine the output power (Pout) in dBm and watts.  Example 3 P1(dB) = 0 dBm P2(dB) = 0 dBm P= P1 + P2 What is the value of P in dBm and watts?  Example 4 Determine the total power when a signal with a power level of 20 dBm is combined with a second signal with a power level of 21 dBm. ELECTRONIC COMMUNICATIONS SYSTEMS  BASIC ELEMENTS OF analog High Frequency Oscillator COMMUNICATION SYSTEM Information Frequency Up- Source and Input Modulator Power Amplifier Converter Transducer High Frequency Communication Local Oscillator Channel Output Frequency Demodulator Amplifier Transducer Down-Converter Analog Signals Are time-varying voltages or currents that are continuously changing such as sine and cosine waves. DIGITAL SIGNALS Are voltages or currents that change in discrete steps or levels.  System Noise and Interference TRANSMISSION MEDIUM TRANSMITTER OR RECEIVER INFORMATION COMMUNICATION CHANNEL RECEIVED SOURCE INFORMATION (INTELLIGENCE) Physical Facility (Metallic or Optical Fiber Cable) or Free-space (Earth’s Atmosphere) ELECTRONIC COMMUNICATIONS SYSTEMS  TRANSMITTER INFORMATION SOURCE (INTELLIGENCE) A transmitter is a collection of one or more electronic devices or circuits that converts the original source information to a form more suitable for transmission over a particular transmission medium.  TRANSMISSION MEDIUM OR COMMUNICATION CHANNEL Physical Facility (Metallic or Optical Fiber Cable) or Free-space (Earth’s Atmosphere) The transmission medium or communications channel provides a means of transporting signals between a transmitter and a receiver. System noise is any unwanted electrical signals that interfere with the information signal. System Noise and Interference  RECEIVER RECEIVED INFORMATION A receiver is a collection of electronic devices and circuits that accepts the transmitted signals from the transmission medium and then converts those signals back to their original form MODULATION & DEMODULATION ANALOG AM FM PM Where: v(t) = time-varying sine wave voltage 𝑣 𝑡 = 𝑽 𝑠𝑖𝑛 (2𝜋𝒇𝑡 + 𝜽) V = peak amplitude (volts) f= frequency (hertz) Θ = phase shift (radians) DIGITAL ASK FSK PSK QAM MODULATION Amplitude modulation (AM) is produced if the information signal is analog and the amplitude (V) of the carrier is varied proportional to the information signal. Frequency modulation (FM) is produced if the information signal is analog and the frequency (f) of the carrier is varied proportional to the information signal. Phase modulation (PM) is produced if the information signal is analog and the phase (θ) of the carrier is varied proportional to the information signal. Amplitude Shift Keying (ASK) is produced if the information signal is digital and the amplitude (V) of the carrier is varied proportional to the information signal. Frequency Shift Keying (FSK) is produced if the information signal is digital and the frequency (f) of the carrier is varied proportional to the information signal. Phase Shift Keying (PSK) is produced if the information signal is digital and the phase (θ) of the carrier is varied proportional to the information signal. 2 Reasons why modulation is necessary in electronic communications: 1. It is extremely difficult to radiate low-frequency signals from an antenna in the form of electromagnetic energy. 2. Information signals often occupy the same frequency band and, if signals from two or more sources are transmitted at the same time, they would interfere with each other. BANDWIDTH AND INFORMATION CAPACITY BANDWIDTH It is simply.. ▪ the difference between the highest and lowest frequencies contained in the information; and ▪ the bandwidth of a communications channel is the difference between the highest and lowest frequencies that the channel will allow to pass through it, that is, its passband. INFORMATION THEORY It is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems. INFORMATION CAPACITY It is a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time. It represents the number of independent symbols that can be carried through a system in a given unit of time. SHANNON’S LIMIT FOR INFORMATION CAPACITY 𝑆 I = information 𝐼 = 𝐵𝑙𝑜𝑔2(1 + ) capacity(bps) 𝑁 B = bandwidth(hertz) 𝑆 𝐼 = 3.32𝐵𝑙𝑜𝑔10(1 + ) 𝑆 𝑁 𝑁 = signal-to-noise ratio(unitless) EXAMPLE For a standard telephone circuit with a signal-to-noise power ratio of 1000(30db) and a bandwidth of 2.7kHz, determine the Shannon limit for information capacity. NOISE ANALYSIS ELECTRICAL NOISE It is defined as any undesirable electrical energy that falls within the passband of the signal. CATEGORIES OF NOISE Correlated Exists only when a signal is present. Uncorrelated Present all the time whether there is a signal or not. UNCORRELATED NOISE External Noise Atmospheric Noise Extraterrestrial Noise Solar Noise Cosmic Noise Man-made Noise UNCORRELATED NOISE Internal Noise Shot Noise Transit-time Noise Thermal Noise THERMAL NOISE 𝑵 = 𝑲𝑻𝑩 N- noise power (watts) B- bandwidth (hertz) K- Boltzmann’s proportionality constant (1.38 x 10-23 joules per kelvin) T- absolute temperature (kelvin) (room temperature = 17C or 290K) THERMAL NOISE 𝐾𝑇𝐵 𝑁(𝑑𝑏𝑚) = 10𝑙𝑜𝑔 0.001 THERMAL NOISE at room temperature.. 𝑁 𝑑𝑏𝑚 = −174𝑑𝐵𝑚 + 10𝑙𝑜𝑔𝐵 EXAMPLE Convert the following temperatures to kelvin: 100C, 0C and -10C. NOISE VOLTAGE 𝑉𝑁 = 4𝑅𝐾𝑇𝐵 EXAMPLE For an electronic device operating at a temperature of 17C with a bandwidth of 10kHz, determine a) Thermal noise power in watts and dBm b) rms noise voltage for 100 internal resistance and a 100 load resistance CORRELATED NOISE It is produced by nonlinear amplification and includes harmonic and intermodulation distortion, both of which are nonlinear distortion. HARMONIC DISTORTION It occurs when unwanted harmonics of a signal are produced through nonlinear amplification (nonlinear mixing). Harmonics are integer multiples of the original signal The original signal is the first harmonic or fundamental frequency HARMONIC DISTORTION 𝑉ℎ𝑖𝑔ℎ𝑒𝑟 %𝑇𝐻𝐷 = ∗ 100 𝑉𝑓𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙 𝑉ℎ𝑖𝑔ℎ𝑒𝑟 = 𝑣22 + 𝑣32 + 𝑣𝑛2 EXAMPLE Determine.. a) 2nd, 3rd, and 12th harmonics for a 1kHz repetitive wave. b) Percent second order, third order, and total harmonic distortion for a fundamental frequency with an amplitude of 8Vrms, a second harmonic amplitude of 0.2Vrms, and a third harmonic amplitude of 0.1Vrms. INTERMODULATION DISTORTION It is the generation of unwanted sum and difference frequencies produced when two or more signals mix in a nonlinear device