Setting arbitrary sample rates for the RX8

Tech Note: TN0870
Product: RPvdsEx
Version: All
Date Added: 2010-03-23

Issue

When using the Check Realizable feature to set an arbitrary sampling rate for the RX8, RPvdsEx calculates rates for PCM converters. However, the RX8 may also be equipped with Sigma-Delta converters. If a PCM rate is used for an RX8 equipped with Sigma-Delta converters, signals will be distorted producing either a flat-line signal or signal drift (if the rates are close).

Workaround

The circuit will work correctly if the correct realizable rate is entered for the type of converters equipped on your RX8. A table of realizable rates supported for the Sigma-Delta converters is available in the System 3 manual. Simply look up the rate and enter it in the RPvdsEx hardware setup dialog.

If you do not wish to enter the value manually you can use the following method

In RPvdsEx, the RX6 arbitrary sample rates are calculated based on supported sigma-delta rates. Select the RX6 Multi-Function processor and enter your arbitrary sample rate. Click the Check Realizable button to approximate the supported sigma-delta sample rate. Finally, select the RX8 Multi I/O processor and click OK. Note that the RX8 supports a maximum sampling rate of 100 kHz.

This will ensure that your arbitrary sample rate is supported by the sigma-delta converters.