--- title: "Analog and digital system block diagrams; linear and non-linear distortion" subject: "Communication Systems" chapter: 1 key: "semester_6/communication_systems:analog-digital-block-linear-nonlinear-distortion" source: https://www.bctengineer.com/q/semester_6/communication_systems/analog-digital-block-linear-nonlinear-distortion site: BCT Engineering --- # Analog and digital system block diagrams; linear and non-linear distortion Communication Systems · Chapter 1: Introduction - Asked in: 2072 Asoj (CS I), 2+2+2 marks - Video: [Block Diagram of Communication System: Basics, Working Details, and Signal Propagation](https://www.youtube.com/watch?v=5tR74NCp3CE) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/analog-digital-block-linear-nonlinear-distortion - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1 ## Question Draw the block diagram of analog communication system and digital communication system. Explain briefly about linear type and non-linear type distortion? ## Short answer Linear distortion alters amplitude/phase of existing frequencies due to non-ideal transfer function, corrected by equalizers. Nonlinear distortion generates new frequencies (harmonics, intermodulation) from nonlinear devices like overdriven amplifiers, reduced by linear operation and feedback. ## Answer #### Analog communication system ```text Source -> Input -> Modulator/ -> Channel transd. Transmitter | <- noise v Dest. <- Output <- Demodulator/ <---+ transd. Receiver ``` #### Digital communication system ```text Source -> Format -> Source -> Channel -> Modulator (A/D) encoder encoder | Channel | <- noise Sink <- Format <- Source <- Channel <- Demodulator (D/A) decoder decoder ``` #### Linear and non-linear distortion - **Linear distortion:** occurs in a **linear** system whose transfer function is not ideal. It does not create new frequencies; it only changes the amplitude and/or phase of existing components. - *Amplitude distortion:* $|H(f)|$ not constant over the signal band, e.g. a cable attenuating high frequencies more. - *Phase (delay) distortion:* phase not linear, so different components are delayed differently; causes pulse spreading and ISI. - Corrected by **equalizers**. - **Non-linear distortion:** occurs when the system's input–output relation is non-linear, e.g. $y = a_1x + a_2x^2 + a_3x^3$ in an overdriven amplifier. It **creates new frequencies**: harmonics ($2f_1$, $3f_1$) and intermodulation products ($f_1 \pm f_2$, $2f_1 - f_2$), which cause crosstalk and interference. Reduced by operating devices in their linear range, negative feedback, or pre-distortion/companding. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which block appears in a digital system but not in the analog system? A. Channel B. Source encoder / channel encoder C. Output transducer D. Demodulator Answer: B. Digital systems include formatting (A/D), source and channel encoders; the analog chain has just transducers, modulator, channel and demodulator. (Key point: Digital system blocks) 2. What does linear distortion do to a signal? A. Creates harmonics B. Creates intermodulation products C. Adds random noise D. Changes only amplitude/phase of existing components without new frequencies Answer: D. Linear distortion changes only amplitude and phase of existing components. (Key point: Linear distortion) 3. Why does an overdriven amplifier y=a1x+a2x^2+a3x^3 cause interference? A. It creates new frequencies such as harmonics and intermodulation B. It shifts all phases linearly C. It only attenuates the signal D. It reduces the bandwidth Answer: A. Non-linear terms generate 2f1, 3f1, f1+-f2, etc., causing crosstalk. (Key point: Nonlinear distortion) 4. Which method corrects linear (amplitude/phase) distortion? A. Companding B. Negative feedback in the amplifier C. Equalizers D. Operating in the saturation region Answer: C. Equalizers compensate non-ideal amplitude and phase response. 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