Calculating quantisation noise and S/N ratio in a PCM system.

Thread Starter


Joined Dec 29, 2016
Hi all,

I am looking for help to answer an assignment question regarding a linear PCM system which has a 7-bit A/D converter and a +-10V input range.

I am asked to calculate the quantisation noise power and the output S/N ratio for a sine wave input of 20V peak to peak.

I am not very confident in my effort so far as I dont think I see where the 20V peak to peak comes in:

Quantisation level, L = 2^7 = 128 levels.

Quantising noise power, ē^2 = U^2/3L^2 = 20^2/3(128)^2 = 400/49152 = 0.0081

S/N ratio = 1.5L^2 = 1.5(128)^2 = 24,576 or 43.9dB