| CPC G01R 31/31708 (2013.01) [G01R 23/02 (2013.01); H03M 1/124 (2013.01)] | 16 Claims |
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1. A signal processing apparatus for mixing a high frequency signal with frequency variation to a predetermined frequency bandwidth, the signal processing apparatus comprising:
an input for receiving an analogue signal under test;
an analogue-to-digital converter for digitizing the received analogue signal under test;
a numerically-controlled oscillator, NCO, for generating a digital signal with a predetermined frequency;
a digital frequency converter for mixing the digitized signal under test provided by the analogue-to-digital converter and the digital representation of a waveform generated by the NCO; and
a frequency tracking device for tracking a frequency of the analogue signal under test or the digitized signal under test,
wherein the NCO is configured to set the predetermined frequency of the NCO based on the frequency tracked by the frequency tracking device,
wherein the frequency tracking device is configured to receive the digital signal provided by the NCO and to compare the digital signal with the frequency of the signal under test which is tracked by the frequency tracking device, and
wherein the predetermined frequency of the digital signal generated by the NCO is continuously adapted in response to a variation of the frequency tracked by the frequency tracking device in real-time,
wherein an offset between the frequency of the signal under test and the predetermined frequency of the digital signal generated by the NCO is applied such that the mixed signal of the digital frequency converter provides a signal with a carrier frequency corresponding to the offset.
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