http://slideplayer.com/slide/4179379/ at slide #18, have a question about pulse

Question

http://slideplayer.com/slide/4179379/

at slide #18, have a question about pulse stufing.

i understand about 'pulse stuffing' and why this we need this.

but i can't get it why 7.2kbps raise to 8kbps.

i think this is because

1. after 4bit ADC, signal output rate is 64kbps

2. there are 8 digital source (from src4 to src11)

3. 64kbps can be chopped to 8 x 8bps.

4. so, at 1 frame, each slot can contain 8kb.

5. we need to raise to fill slot -> raise 7.2 to 8k using pulse stuffing

am i right? or please write your explanation. Thanks.

Explanation / Answer

Yes, you are correct. When we design the time division multiplexer for the given diagram, we have 11 sources:

Each of the analog signals is converted into 4 bit PCM word. The output rate of the converter is 64 kbps. We need to merge it with the 8 digital signals. In the diagram, the commutator (written as scan operation) is rotating at 8 KHz. There are 16 terminals. Let's connect the 64 kbps from the converter to 8 of those terminals. So, each terminal in this commutator is effectively 8 kbps. Now we are left with 8 more terminals and 8 inputs of 7.2kbps. How do you connect it without causing problems in synchronization? You need to add extra bits and increase the input from 7.2kbps to 8 kbps. This way all the terminals are connected to 8 kbps inputs. This preserves synchronization.

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