Forum Discussion
Honored Contributorphase difference 2 signals.
is possible whit fpga FFT or similar metod measure a phase difference from 2 PULSED-sinusoidals signals?
the freq of signals is 60MHz but the duration of signals is 0.5uSEC, and the PRF of pulsed signals is 1800Hz. tnx Luca19 Replies
Altera_ForumI/Q demodulation is done my multiplying the input signal with 0° and 90° reference sine. If you manage to sample the input at fs = 240 MHz, the operation simplifies to processing the odd and even samples. Gating according to the signal enevlope would be necessary in any case.
- Altera_Forum
you can do digital one if you afford the speed
- Altera_Forum
but do i need a IQ anoligic demodulator?
- Altera_Forum
That is a good point. You mean demodulate signal to its two I/Q components and demodulate reference similarly then check phase/amplitude.
It eventually depends on application resolution and noise level. Demodulation may need filtering the sideband. - Altera_Forum
In my opinion, FFT is a rather longwinded method to analyze the phase of a known frequency sine signal. Quadrature demodulation would allow an accurate amplitude and phase measurement.
- Altera_Forum
If you have matlab, you can try this code (not tested):
%assuming Fs = 240Msps %signal 1 offset = 100; x1 = sin(2*pi*(0+offset:200000+offset)*60/240); x1(1000:1000:end) = 0; %switch off %ref xref = sin(2*pi*(0:200000)*60/240); y1 = fft(x1,1024); y2 = fft(xref,1024); A1 = abs(y1); A2 = abs(y2); ph1 = angle(y1); ph2 = angle(y2); you will then check A/ph at relevant bin - Altera_Forum
tnx to all!
i must analize 3 (or 4) PULSED-RADAR-signals. The minimum duration of signals is 0,5 uSEC (typ 1 uSEC). i need to measure the amplitude and and the phase of these signals, referenced at 1 CW (continuos sinusoidal wave) generated by 1 reference-local-oscillator (60 MHz). In analogic circuit i have not problem, using AD8302(analog devices chip), but i need do it in digital world whit fpga.. tnx!! - Altera_Forum
Is there any reason why these two signals are pulsed sinusoids?
If this is a ranging application, then an FM chirp (linear FM pulse) would be more appropriate. Pulse compression of the FM chirp (correlation) then results in delta-function like responses (with a width determined by the pulse bandwidth). The 'time delay' between the delta functions can then be determined. Pseudo-random sequences can also be transmitted and pulse compressed in this manner. What are you trying to do? Cheers, Dave - Altera_Forum
1) time domain option is unlikely to have good resolution since 60MHz running at sampling freq of say 240MHz means only 4 samples per cycle.
2) fft option may be better. You can model that in matlab: generate stimulus then apply fft and see phase.
