Generating a Chirp (sweep) signal using A10Soc and FMC-DAQ2 Boards

What are the requirements of the chirp? Can the ramp (or similar) fit into a data buffer or does it need to be generated in logic?

-Travis

Hi Travis! 

If its not too much trouble, I was wondering if you or anyone could provide me with some guidance as to how should I begin implementing a sweep signal which spans from 0-5Ghz (preferably in logic)?

Thank you so much for your time!!

Regards,

Udai 

Since the required frequency sweep is really large im not sure if this can be implemented by fitting the ramp in a data buffer? 

5 GHz is outside the bounds of DAQ2. The DACs (AD9144) have a max sample rate of 2.8 GS/s.

-Travis

Oh yes, I'm sorry I should've been clearer about what I'm doing.  So we are using the daq2 kit just for testing and will eventually migrate to AD9163, which is when we have to implement the 5Ghz chirp. 

For now I only want to generate a 1Ghz (or max possible) chirp on the daq2 with the goal of expanding it upto 5ghz when we migrate to our custom pcb. 

Once again, thank you so much for your time and effort!! I really really appreciate the support!

Regards,

Udai

Oh yes, I'm sorry I should've been clearer about what I'm doing.  So we are using the daq2 kit just for testing and will eventually migrate to AD9163, which is when we have to implement the 5Ghz chirp. 

For now I only want to generate a 1Ghz (or max possible) chirp on the daq2 with the goal of expanding it upto 5ghz when we migrate to our custom pcb. 

Once again, thank you so much for your time and effort!! I really really appreciate the support!

Regards,

Udai

The easiest thing to do is to generate your chirp in DDR. DDR will limit the sequence length to  ~2^21.
If you need to do things in fabric you will need to create a vectorized chirp generator since no FPGA can run logic at speeds you require serially.

-Travis

Thank you so much for your reply! 

Would it be possible to guide me as to how I can generate the chirp in the DDR? I will start with this and then in parallel try to create the vectorized chirp generator.

Just some basic steps of how to do it would be absolutely amazing, thank you so much for helping me out with this! 

2^21 means that I could generate chirps of upto 1Ghz? 

Thank you so so much once again for your time and effort, I really appreciate the help! I have no idea what I'm doing and getting this done is a very overwhelming job, thank you once again! 

There are many existing libraries to create chirps. For example: https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.chirp.html

You can generate a data vector and pass that through pyadi-iio (https://wiki.analog.com/resources/tools-software/linux-software/pyadi-iio) to DAQ2. Here is a basic example of DAQ2 in pyadi-iio: https://github.com/analogdevicesinc/pyadi-iio/blob/master/examples/daq2.py

Here is some doc about interfacing with  the buffers: https://analogdevicesinc.github.io/pyadi-iio/buffers/index.html

-Travis

Hello Travis! 

Thank you so much for those extremely helpful resources, this is exactly what I was looking for at this point! 

I got the DAQ2 pyadi-iio example that you provided to work on the board, so I think the environment and all the dependencies are installed correctly on my machine. 

However, I'm unable to get the chirp to work (using the chirp library you provided). If I set the sample rate of the chirp to the daq2.sample_rate then I get this error (for even a chirp of just 5 hz): 

However, If I lower the sampling rate then I get no output from the DAC, its just constant noise. I'm probably doing something incredibly wrong with calling the libraries, I was wondering if you could have a look at it? I've attached the file I'm currently trying to run. 

Thank you once again for your time, effort and support! I really appreciate the help! 

- Udai 

import time
import adi
import matplotlib.pyplot as plt
import numpy as np
from scipy import signal
from scipy.signal import chirp, spectrogram


#Set daq parameters
daq = adi.DAQ2(uri="ip:192.168.0.4")

#destroy buffer and enable channel 0
daq.tx_destroy_buffer()
daq.tx_enabled_channels = [0]

# Create a chirp
fs = daq.sample_rate
T = 1
t = np.arange(0, int(T*fs)) / fs
w = chirp(t, f0=1500, f1=1495, t1=T, method='linear')

# Enable cyclic buffers
daq.tx_cyclic_buffer = True
# Send data cyclically
daq.tx(w)


# Collect data 
fs = float(daq.sample_rate)
for r in range(10):
    x = daq.rx()
    print (x[0])
    f, Pxx_den = signal.periodogram(x[0], fs)
    plt.clf()
    plt.semilogy(f, Pxx_den)
    plt.ylim([1e-11, 1e2])
    plt.xlabel("frequency [Hz]")
    plt.ylabel("PSD [V**2/Hz]")
    plt.draw()
    plt.pause(0.05)
    time.sleep(0.1)

plt.show()

The default sample rate of DAQ2 is 1 GS/s. With your code, w will be a 1e9 length vector which is var larger than the max input buffer size which is ~2^21.

Also, DAQ2 has a 16-bit DAC. Make sure your input data maximizes this range by providing samples that are [-2^15 to 2^15-1]. By default I believe chip scales data [-1,1].

-Travis