How does the output signal frequency relate to the Internal Timebase/Clock/VCXO? Hardware: Signal Sources (AWG/FG/AO)>>Arbitrary Waveform and Function Generators>>PXI-5421
Problem: How does the output signal frequency relate to the Internal Timebase/Clock/VCXO? Solution: The frequency accuracy of the generated signal on Signal Generator modules directly corresponds to the frequency accuracy of the Internal Timebase (sometimes referred to as Clock or VCXO). Signal Generator modules are all digital in the generation of the signals through the use of a digital to analog converter (DAC). The DAC will generate samples of a waveform with a Sample Clock Rate derived from the Internal Timebase. There are three main methods that Sample Clock Rate is derived from the Internal Timebase. The Sample Clock Rate can be almost directly clocked by the Internal Timebase. This is the case for a Sample Clock Rate that is equal to the Internal Clock frequency, and usually the maximum Sample Clock Rate. The Sample Clock Rate can be an integer divided down version of the Internal Timebase through the use of a digital counter circuit. The Sample Clock Rate can be a high resolution frequency derived through a Direct Digital Synthesis circuit, with the Internal Timebase as the main source of clocking. In each of these cases, the Sample Clock Frequency is ultimately derived from the Sample Clock Timebase and as such, will have the same Frequency Accuracy as the Internal Timebase. Taking this a step further, a sine wave generated with the DAC will have the same Frequency Accuracy as the Internal Timebase. For example, creating a sine wave that has 10 samples per cycle, will have a signal frequency of one tenth the Sample Clock Rate and will be as accurate as the Sample Clock Rate and the Internal Timebase are. Related Links: Attachments:
Report Date: 04/01/2004 Last Updated: 04/16/2004 Document ID: 380ATUOL |
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