A little information about the PCM Encoder module on the Emona Telecoms-Trainer 101
The PCM Encoder module uses a PCM encoding chip (called a codec) to convert analog
voltages between -2V and +2V to an 8-bit binary number. With eight bits, it’s possible to
produce 256 different numbers between 00000000 and 11111111 inclusive. This in turn means
that there are 256 quantisation levels (one for each number).
Each binary number is transmitted in serial form in frames. The number’s most
significant bit (called bit-7) is sent first, bit-6 is sent next and so on to the least significant bit
(bit-0). The PCM Encoder module also outputs a separate Frame Syschronisation signal (FS)
that goes high at the same time that bit-0 is outputted. The FS signal has been included to help
with PCM decoding (discuss in the preliminary discussion of Experiment 13) but it can also be
used to help “trigger” a scope when looking at the signals that the PCM Encoder module
generates.
Figure 1 below shows an example of three frames of a PCM Encoder module’s output
data (each bit is shown as both a 0 and a 1 because it could be either) together with its clock
input and its FS output.
Figure 1
EE 4-05: PCM modulation and demodulation Page 3 / 23
The experiment
In this experiment you’ll use the PCM Encoder module on the Emona Telecoms-Trainer 101 to
convert the following to PCM: a fixed DC voltage, a variable DC voltage and a continuously
changing signal. In the process, you’ll verify the operation of PCM encoding and investigate
quantisation error a little.
Equipment
• Emona Telecoms-Trainer 101 (plus power-pack)
• Dual channel 20MHz oscilloscope
• two Emona Telecoms-Trainer 101 oscilloscope leads
• assorted Emona Telecoms-Trainer 101 patch leads