CMX983 Datasheet, PDF (29/93 Pages) CML Microcircuits – Programmable Channel Filter

Analogue Front End (AFE) for Digital Radio
9.2 Receive Channel Filters
CMX983
Figure 13 Rx Channel Filters
The CMX983 has two main channel filters (Figure 13). Within each channel filter, the signal is decimated
twice. Data from the ADC passes into a sinc^N filter, a bit selector circuit and a vernier phase adjustment
before the first downsampler. The resulting signal then passes into a programmable 128-tap FIR filter, a
second bit selector and the second downsampler before being passed to the serial port for transmission to the
host processor. The serial port data is formatted as 16-bit 2’s complement values. Each stage in the Rx
channel (sinc filter, bit select, vernier adjust, downsample and FIR filter) is programmable.
Sinc filter
The bitstream produced by each sigma-delta modulator has a characteristic high-pass filtered noise profile.
The sinc filter attenuates this quantisation noise, along with any other noise or unwanted signals coming from
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