Frequency Translation

NI High-Speed Digitizers Help (NI-SCOPE)

Edition Date: January 2017

Part Number: 370592AB-01

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Frequency translation moves the Nyquist frequency spectrum of the acquired signal by the amount specified by the Center Frequency attribute. This is accomplished by multiplying the acquired data stream with the output of the numerically controlled oscillator (NCO). The NCO is a digital circuit that creates two sine waves of the same frequency (the Center Frequency) with two independent phases. You can use the Center Frequency attribute to set the carrier frequency. The I phase cosine waveform is multiplied by the I signal path, and the Q phase cosine waveform is multiplied by the Q data path. The I and Q phases are programmable from 0° to 360° by setting the Frequency Translation Phase I and Frequency Translation Phase Q attributes/properties. Both the frequency and the phases can be updated during acquisition. You can consider the values of the Frequency Translation Phase I/Q attributes as the start phase of the NCO waveforms. The NCO outputs start at the specified phase values when the start trigger is received. Normally, the I and Q phases would be set to 0° and 90°, respectively, but the flexibility allows you to correct any externally-induced impairments in the IF signal.


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