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Digital Down Converter

*NEW*
DDC firmware available on ACQ1001/ACQ425. Sample up to 2MSPS, LO frequency to 500kHz.
Please contact D-TACQ for details. email: info@d-tacq.co.uk

Digital Downconverter DDCworld firmware is available for ACQ196CPCI and soon for ACQ132CPCI
The DDC is used in systems where incoming signal is modulated on a fixed frequency carrier.
The DDC mixes incoming data with a Local Oscillator LO to reduce the carrier centre frequency down to base band, to allow extraction of the original signal at a lower data rate.
The LO is a fixed ratio of the input sample rate Fs (Fs/4), and the DDC may be tuned by adjusting the sample rate.
The tuning range is therefore:

Model Tuning Range Internal Clock step size
ACQ196CPCI-96-500 DC to 125kHz 10kHz
ACQ132CPCI-32-02C 250kHz to 2.5MHz 0.25kHz
ACQ132CPCI-32-32F 250kHz to 10MHz 0.25kHz

After mix-down, the data is passed through a series of low pass filters, to remove out of band signal and eliminate aliasing.
The signal is decimated, reducing the output data rate. The amount of decimation that is possible depends on the signal bandwidth.
Filtering and decimation may be adjusted in the design to accommodate a range of user bandwidths.
In general, the lower the output bandwidth, the higher the degree of decimation possible, so the less data the downstream system has to deal with.

Application note shows a sonar system receiver implemented using a
96 Channel Digital Downconverter