I am capturing TDM audio data streamed at 10MHz. In order to capture this high MHz data, I need to sample Saleae at 250MS/s. If I set a sample rate to 125MS/s or below, I get bad audio captures with glitches in it.
On a Kingst Logic Analyzer, I can set the sample rate to 20MS/s(Nyquist frequency) and it works fine. I find it very disturbing that I have to set the sample rate to 250MS/s on Saleae. Is there any work around for this ?
Please note that, TDM lines are drawn out from a customer HW with very thin wires. I tried increasing the drive strength of the pins, but that didn’t help.
I can capture at 100MS/s on another Evaluation Mother Board with proper GPIO pins. But this is still very high.
I would like to capture audio for long duration (5-10 mins) and I feel that the high MS/s is a limiting factor. Can you please advise on what can be done.
@rohit.walavalkar Thanks for reaching out about this. Are you capturing data as digital or analog? Our sampling rate recommendations are summarized in the support article below:
Typically, sampling at 4x the frequency of your signal should suffice (assuming you are capturing data digitally, not analog). The glitches might be due to slow rising/falling edge times caused by pullup resistors (common in I2C). The Logic Pro models are implemented with comparators instead of standard CMOS buffers found on Logic 4 and Logic 8. This makes the input-low and input-high voltages very close to each other, and what might be causing the glitches during digital transitions from LOW to HIGH and vice versa.
Does enabling the glitch filter help clean up the incoming signal?
Software Glitch Filter - Saleae Support
Does changing the voltage threshold setting (which changes the digital voltage threshold to half the specified value) help clean up the incoming signal?
Supported Voltages - Saleae Support
One other thing to note about your comment below:
Memory usage for digital recordings depends on (1) the number of digital channels, (2) toggles/sec of incoming data, and (3) the duration of the capture. The sampling rate setting has no effect, though, using too low of a sampling rate may not be able to catch all relevant toggles/sec.
Contrary to analog captures, digital captures will only store data in memory when a toggle occurs on the digital channel. For this reason, it is typically recommended to sample at the highest digital sampling rate since it will not use any more memory than using a slower digital sampling rate (assuming the same data is captured).