Problems Synchronizing Waveforms Across Multiple Devices

Tech Note: TN0145
Product: RPvdsEx
Version: All
Date Added: 2004-09-23


Problems with synchronizing waveforms (such as a triangle wave) and with generating proper delays on two devices are typically a result of differing sample rates. The device with the higher rate can generate waveforms or delays with more resolution than the device at a lower rate. See Tech Note #0143 for more information.

Each TDT device has a fixed set of sample rate capabilities. The use of high- performance sigma-delta DACs makes supporting completely arbitrary rates unreasonable in some devices. For example, the RV8 does not use sigma-delta DACs so it can offer any rate (derived from 25 MHz) while the RX6 uses sigma-delta DACs and thus supports a limited set of sample rates. The setup dialog in RPvdsEX will always return the true available rate for any device when the 'Check Realizable' button is clicked.


TDT software that offers arbitrary delays always bases the actual delay specified on the lowest sample rate used. If the rates are not related by a simple factor of two, four, etc., the actual delays that can be offered can be unsatisfactory.


If possible, use standard sample rates that will be related by a simple factor of two, four, etc. If you are using any of the non-linear generator components, be aware that only frequencies related to the sample rate by an integer multiple can be generated.