Generating chirp with dsp.NCO system object in frame-based processing mode
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Dear all,
I want to generate a chirp with a dsp.NCO instance by inputting a column vector of phase increments in order to achieve frame-based processing. Most of the code I took from the example. The phase offset is constant and therefor set as property.
Fstart = 50; % start freq of chirp
Fstop = 1500; % stop freq of chirp
df = 0.05; % Frequency resolution = 0.05 Hz
minSFDR = 96; % Spurious free dynamic range >= 96 dB
Ts = 1/8000; % Sample period = 1/8000 sec
dphi = pi/2; % Desired phase offset = pi/2;
Fmom = linspace(Fstart,Fstop,1/Ts)'; % Momentary frequency
% Design the NCO source.
Nqacc = ceil((minSFDR-12)/6);
Nacc = ceil(log2(1/(df*Ts)));
phOffset = 2^Nacc*dphi/(2*pi);
nco = dsp.NCO('PhaseOffsetSource','Property',...
'PhaseOffset', phOffset,...
'NumQuantizerAccumulatorBits', 14,...
'SamplesPerFrame', 1/Ts, ...
'CustomAccumulatorDataType', numerictype([],Nacc));
% convert freqs to phase increments
phIncr = int32(round(Fmom.*Ts.*2.^Nacc));
% generate chirp signal with colomn input, one step only
y = nco(phIncr);
%plot chirp
t = 0:Ts:(1/Ts-1)*Ts;
plot(t,y)
In the plot you'll see that the output of the NCO remains at the start freq and does not provide the chirp.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1709986/image.png)
Who can help me to get the dsp.NCO instance work with variable freqs in framebased mode?
Patrick
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