Digital Communication
First week
A. The PCM Transmitter and Receiver
1. Plot a graph with the A/D converter input and output voltages as axes. What is the quantization step size?
The quantization step size = (83 – 57) / (1.6 + 0.5) = 12.4 V
2. What should be the duration of a timing frame, given the clock frequency in Transmitter Timing Logic previously? Is it the same as that measured from the waveform at test point 4?
The frequency we used is 16kHz. So the duration of the time frame should be 1/16000 = 62.5μs which is more or less the same as the period measured from waveform at test point 4 of 62 μs.
3. Are the sinewaves faithfully reproduced at the output of the receiver? How much delay is observed? What sampling frequency is used by the system? (Hint: Examine the signal at test point 50.) What is the maximum frequency that can be sent using this system if aliasing is to be avoided?
The sinewaves are faithfully reproduced at the output of the receiver. The reconstructed waveform has the phase shift of 90∘ and delay of 200μs.
By examining the signal at test point 50, the sampling frequency used by the system is 15.99 kHz.
According to the sampling theorem, the maximum frequency that can be sent using this system if aliasing is to be avoided is 8 kHz.
4. Do you observe any distortion due to quantization? How serious is the distortion introduced?
There is no distortion observed.
B. Synchronization in PCM Systems
5. Explain why the source and reconstructed waveforms look different. How does the connection between TX T0 OUTPUT and RX SYNC INPUT achieve frame synchronization?
If TX T0 OUTPUT and RX SYNC INPUT are connected, frame synchronization can be achieved. So the start of each wave can be detected and the reconstructed waveform would be the same as the source. However, if there is no connection between TX T0 OUTPUT and RX SYNC INPUT,...
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