Oversampling filter improves SNR

The "FS_Filter" or "Final Stage Filter" firmware upgrade to the ACQ196CPCI digitizer implements a simple accumulate/decimate/shift filter stage in each of the 96 channels in the data stream. This follows the model used successfully on ACQ132CPCI. For applications that do not require the full 250KHz bandwidth of ACQ196CPCI, the FS_Filter can improve SNR as well as anti-alias performance by pushing up the Nyquist limit of the system. The filter can also provide an element of digital gain control. The user can specify NACC (input samples to accumulate per output word) and SHR (a right shift value to keep scaling).

Examples.

NACC=32 SHR=5 : ISR=500kHz, OSR=15kHz, ENOB +2.5 bits GAIN=1
NACC=32 SHR=4 : ISR=500kHz, OSR=15kHz, ENOB +2.5 bits GAIN=2
NACC=25 SHR=4 : ISR=500kHz, OSR=20kHz, ENOB +2.5 bits GAIN=25/16
NACC=16 SHR=4 : ISR=500kHz, OSR=31.25kHz, ENOB +2.0 bits GAIN=2
NACC=04 SHR=2 : ISR=500kHz, OSR=125kHz, ENOB +1.0 bits GAIN=1
NACC=01 SHR=0 : ISR=500kHz, OSR=500kHz, default configuration