RTS control latency high
Artemiy Dmitriev wrote in chat:
This high-speed CDS work is very interesting. Did anyone measure the actual time delay you get when passing a signal through CDS with increased clock frequency?
We have delay of about 200 us at our standard 65k setup if we connect input to output directly in the iop model. It gives a linear phase-frequency dependence with phase crossover frequency of about 2.5 kHz. About half of this delay should be coming from AA/AI filters, but the other half (≈100 us) can only come from the front-end itself. This is still much longer than suggested by e.g. slide 8 here , but I guess it is consistent with what others have.
Since we are working with tabletop setups, we are obviously always looking for ways to increase the bandwidth of CDS beyond 1-2 kHz by a factor of ≈10, and it does not seem that there any hardware limitations for that. The IOP model takes 1-2 us to complete with 2-8 filter banks on our machines. We would certainly consider buying faster ADC/DAC cards if this would help us to increase the bandwidth, but we obviously would like to know in advance whether it would help or not.
We should probably aim for no worse than 50 us. We need to develop a reliable way of measuring the latency of A2D -> DAC. Ideally, we could measure distinct latencies from the control loop, the DMA buffers, and analog response of the DAC.