Virtual Labs

Pulse Amplitude Modulation (PAM), Pulse Width Modulation (PWM), Pulse Position Modulation(PPM), Pulse Coded Modulation & their Demodulation

1. In Pulse Amplitude Modulation (PAM), what is a critical trade-off encountered when increasing the signal bandwidth to mitigate inter-symbol interference (ISI)?

a: Improved spectral efficiency but increased noise susceptibility Explanation

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b: Reduced quantization error but higher transmission delay Explanation

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c: Lower distortion but reduced amplitude resolution Explanation

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d: Better noise immunity but higher bit error rate Explanation

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2. In high-frequency switching applications, what makes Pulse Width Modulation (PWM) inherently less power-efficient compared to other modulation schemes?

a: High-frequency harmonics result in greater switching losses Explanation

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b: The need for linear amplifiers increases energy demands Explanation

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c: PWM requires higher sampling rates than PAM Explanation

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d: Duty cycle variations distort the signal envelope Explanation

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3. In Pulse Code Modulation (PCM), how does increasing the number of bits per sample impact both the bandwidth requirement and the Signal-to-Quantization-Noise Ratio (SQNR)?

a: Increases bandwidth linearly while SQNR improves logarithmically Explanation

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b: Reduces bandwidth but degrades SQNR exponentially Explanation

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c: Leaves bandwidth constant and improves SQNR linearly Explanation

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d: Increases bandwidth exponentially and reduces SQNR logarithmically Explanation

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4. In Pulse Position Modulation (PPM), how does timing jitter specifically impact the symbol detection process in a non-ideal receiver?

a: It randomly shifts the phase of the detected pulses Explanation

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b: It causes inter-symbol interference due to overlapping symbols Explanation

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c: It introduces uncertainty in pulse arrival times, increasing symbol error probability Explanation

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d: It reduces the amplitude of received pulses, causing clipping Explanation

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5. In PCM, why is there a practical limit to increasing quantization levels beyond a certain point, even if bit rate is not a constraint?

a: Thermal noise sets a noise floor below which quantization gains are negligible Explanation

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b: Increasing levels increases distortion due to aliasing Explanation

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c: Too many levels cause amplifier saturation in the encoder Explanation

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d: The dynamic range of the source signal collapses with finer quantization Explanation

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6. What is the primary non-ideality introduced by a nonlinear modulator in a PAM system from a frequency domain perspective?

a: Spectral nulls at harmonics of the pulse frequency Explanation

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b: Generation of intermodulation products and harmonic distortion Explanation

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c: Increase in channel noise floor Explanation

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d: Reduction in spectral efficiency due to pulse spreading Explanation

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7. Why is Pulse Width Modulation (PWM) more suitable for motor control applications compared to PAM?

a: PWM minimizes power loss during switching and allows efficient average voltage control Explanation

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b: PWM provides higher resolution of control at lower voltages Explanation

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c: PWM reduces electromagnetic interference compared to PAM Explanation

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d: PWM signals are easier to encode into digital logic levels Explanation

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8. In a noisy communication channel, which modulation scheme among PAM, PWM, PPM, and PCM is most susceptible to amplitude noise and why?

a: PAM, because it directly encodes information in amplitude which is distorted by noise Explanation

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b: PPM, because pulse timing is affected by amplitude variations Explanation

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c: PCM, because noise causes quantization level hopping Explanation

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d: PWM, because duty cycle depends on signal amplitude Explanation

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9. In a PCM system, undersampling a band-limited signal results in which primary artifact, and how does it manifest in the frequency domain?

a: Aliasing, where high-frequency components fold into the baseband Explanation

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b: Quantization distortion, leading to spectral harmonics Explanation

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c: Bandwidth broadening due to spectrum repetition Explanation

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d: Inter-symbol interference from overlapping samples Explanation

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10. In high-speed PPM systems, what is a key reason for preferring higher-order modulation despite its susceptibility to timing jitter?

a: It reduces symbol duration, increasing robustness to timing noise Explanation

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b: It allows higher data throughput without increasing pulse rate Explanation

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c: It mitigates phase noise in long-distance transmission Explanation

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d: It simplifies the demodulation circuitry by reducing synchronization requirements Explanation

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