Data Acquisition (DAQ) and Control from Microstar Laboratories

Knowledge Base: Processing

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Q10054 Maximum filter cutoff frequency in different versions of iDSC support

Tags: Help, iDSC, filter cutoff

Applies to: iDSC, maximum filter cutoff

At the maximum sample rate of 153600 Hz, why is the maximum cutoff frequency 61440 Hz in an older version of iDSC support and 75264 Hz in a newer version?

The maximum cutoff of 75264 Hz is a new feature introduced with iDSC support version 5.10, which is on DAPtools software package version 3.40 and later. For the maximum iDSC sample rate of 153600 Hz, 75264 Hz is 98% of the Nyquist frequency. The configuration works at maximum rate without aliasing because the ADC includes a hardware filter that cuts off at 92.8% of the Nyquist frequency, and fully attenuates everything at the Nyquist frequency and beyond. The 75264 Hz rate allows the maximum possible bandwidth through the analog front end of the iDSC board. Since a high frequency rolloff at the highest frequencies is already determined by the hardware filters, a user-specified filter has essentially no effect when its cutoff frequency is higher.