NI PCI-5922 Clocking
- Updated2023-09-20
- 2 minute(s) read
NI PCI-5922 Clocking
The clock circuitry on the NI PCI-5922 offers versatile clocking options. You can use the phase-locked loop (PLL) circuit on the NI PCI-5922 to phase lock the internal 120 MHz oscillator with a reference clock from another module on RTSI 7, or with an external reference clock that you provide. The following diagram shows the clocking options of the NI PCI-5922.
Sample Clock
The sample clock is sent to the ADC on each channel and to the input timing engine. The NI PCI-5922 has an onboard voltage controlled crystal oscillator (VCXO) running at 120 MHz that is the sample clock on the device. When using the onboard 120 MHz oscillator, you can choose either free-run mode or PLL mode. In free-run mode, the sample clock is generated from the calibrated 120 MHz frequency of the VCXO. In PLL mode, the NI PCI-5922 phase locks its 120 MHz oscillator to the supplied reference clock. The PLL mode is useful when you synchronize the NI PCI-5922 with other devices in a measurement system.
Reference Clock
The reference clock is used in the NI PCI-5922 PLL circuit to synchronize the sample clock to the reference clock. The NI PCI-5922 can accept a reference clock from its front panel (CLK IN) as well as from RTSI 7 (RTSI Clock) on the RTSI bus or the internal 10 MHz reference clock. This reference clock can be any frequency from 1 MHz to 20 MHz if it is provided to CLK IN or to RTSI 7. The internal reference clock is always a 10 MHz clock. The frequency stability of the sample clock matches that of the PLL reference clock when the two are phase locked. In turn, phase locking synchronizes clocks of multiple devices that are phase locked to the same reference clock. The default setting for the NI PCI-5922 reference clock is None, or not to use a reference clock.
Exporting Reference Clock
If you are using an external reference clock to phase lock the internal sample clock, you can export the reference clock for use with other instruments. For more information on exporting the reference clock, refer to the NI PCI-5922 Routing Matrix.