As electronic products continue to evolve in complexity, the requirement to synchronize multiple instruments to test or characterize a device becomes even more necessary. Synchronization is key for either synchronizing instruments of the same type for channel expansion, or for tightly correlating the input and output of two different instruments. Mixed-signal test systems require the use of at least two of the three instruments (digitizer, arbitrary waveform generator, and digital waveform generator/analyzer). Additional applications requiring synchronization are baseband I/O signal generation and acquisition for communications, RGB video signal generation and acquisition for consumer electronics, digital waveform generation and acquisition of 24 channels for 24-bit ADC and DAC test, and many more.
The PXI modular instrumentation platform has an integrated backplane architecture designed to meet the needs of engineers synchronizing multiple instruments in test. The backplane has three main features for synchronization—the 10-MHz reference clock, trigger bus, and star trigger.
10-MHz Reference Clock
The PXI backplane provides a built-in common reference clock for synchronizing multiple modules in a measurement or control system. The clock is distributed to each peripheral slot with equal-trace-length lines, yielding &1 nsec of slot-to-slot skew. The accuracy of the 10-MHz clock is typically ±25 ppm, making it a relatively reliable clock for synchronization applications that rely on phase lock looping (PLL) methods. If a more accurate reference clock is needed, a user can insert a PXI timing and synchronization module with an oven-controlled crystal oscillator (OCXO) clock source into slot 2 of the chassis. This overrides the backplane clock and can increase the accuracy to ±50 ppb. Common application of the 10-MHz reference clock is the synchronization of measurement devices that operate at sample rates from 1 MHz to several GHz.
The PXI trigger bus provides eight lines for inter-module communication and synchronization. The bus can be used to pass trigger, clock, or event signals from one module to any number of modules.
The star trigger bus provides independent dedicated lines from slot 2 to each of up to 13 peripheral slots in a PXI system. The star trigger lines are matched in propagation delay to within 1 nsec, providing very precise triggering for high-speed synchronization.
PXI Timing and Synchronization modules can be installed in slot 2 of PXI chassis for synchronization of multiple PXI systems. The module provides for the import and export of triggers and clocks, as well as clock synchronization with Phase Lock Looping methods. This allows for massive synchronized channel expansion into the thousands, as well as synchronization of measurement systems across facilities.
For more info on PXI, visit the PXI Systems alliance at www.pxisa.org.