Digital Down Converter
Digital Downconverter DDC 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:
||Internal Clock step size
||DC to 125kHz
||250kHz to 2.5MHz
||250kHz to 10MHz
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