SonixDAQ Receive Bandwidth
The receive bandwidth of the DAQ can now be adjusted through the daq API. The low pass filter (anti-aliasing) cut-off frequency can be set through daqSequencePrms.lowPassFilterCutOff as a function of sampling frequency (which is either 40 or 80 MHz). The high pass filter (removes the DC) cut-off frequency can be set through daqSequencePrms.highPassFilterCutOff as a function of low pass filter's cut-off frequency. Please see the daq_def.h file for more details.
In order to study and measure the receive bandwidth of the SonixDAQ for both 40MHz and 80MHz sampling frequencies, a series of experiments were performed. A signal generator was used for this purpose with the following settings:
- Continuous wave sinusoidal signal was inject to all the channels at the same time,
- The amplitude of the signal was set to be 20 mVpp for each channel (peak to peak),
- The frequency of the signal was changed from 1MHz to 20MHz in steps of 1MHz for 40MHz sampling and from 1MHz to 40MHz in steps of 1MHz for 80MHz sampling.
For each frequency, the signal was injected into the DAQ connector. The channel data corresponding to each signal was then recorded for off-line processing. This process was repeated for all the frequencies. In all the experiments, the decimation was set to be zero.
Signal Processing and Results
Recorded channel data were processed off-line. For all the injected signals, Fourier analysis was performed on each channel data and the resulting spectrum were average over all 128 channels to estimate the transfer function.
The estimated transfer function for both 40MHz sampling and 80MHz sampling are shown in the figure below. The results are displayed in dB. Separate normalization was used for each graph.
DAQ with 40MHz sampling
- -10dB drop from 4 to 20MHz,
DAQ with 80MHz sampling
- -15dB drop from 4 to 40MHz.