Hi Patrick,
you can try using the following code:
Fstart = 50; % Start frequency of chirp
Fstop = 1500; % Stop frequency 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, ... % Process one sample at a time
'CustomAccumulatorDataType', numerictype([], Nacc));
% Convert frequencies to phase increments
phIncr = int32(round(Fmom .* Ts .* 2.^Nacc));
% Generate chirp signal
y = zeros(length(phIncr), 1);
for k = 1:length(phIncr)
y(k) = nco(phIncr(k));
end
% Plot chirp
t = (0:length(y)-1) * Ts;
plot(t, y);
xlabel('Time (s)');
ylabel('Amplitude');
title('Generated Chirp Signal');
Key Changes:
- Changed "SamplesPerFrame" to 1 to process one sample at a time, ensuring the phase increment is updated for each sample.
- Added a loop to generate the chirp signal sample-by-sample using the "nco" object.
- Adjusted the plot to reflect the entire duration of the chirp signal.
