Category: Analog

In an earlier post, it was mentioned that delta modulator without the quantizer is identical to convolving an input sequence with . Let us first try to validate that thought using a small MATLAB example and using the delta modulator circuit shown in Figure 9.13a of DSP-Proakis [1].

% delta modulation
xn = sin(2*pi*1/64*[0:63]);
xhatn = 0; 

for ii = 1:length(xn)

dn = xn(ii) - xhatn;
dqn = dn; % no quantizing done, when quantizing is done: dqn = 2*(dn>0) - 1;
xqn = dqn + xhatn; 

% dump of transmitter variables
dnDump(ii) = dn;
dqnDump(ii) = dqn;
xqnDump(ii) = xqn;
xhatnDump(ii) = xhatn; 

xhatn = xqn; %  variable storing one-sample delayed version of xn

% receiver
rn = rn + dqn;
rnDump(ii) = rn;

end 


% implementation by convolving with [1 -1] 

d1n = conv(xn,[1 -1]);
diff = (dnDump - d1n(1:64))

Continue reading “Sigma delta modulation”