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CS5376 查看數據表(PDF) - Cirrus Logic

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CS5376 Datasheet PDF : 122 Pages
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CS5376
Stage 5 of Sinc2 can be modeled as a 6th order sinc
filter with a decimate by 2 output. The time domain
coefficients are [1, 6, 15, 20, 15, 6, 1], and the fre-
quency domain model is [(sin x)/x]6.
8.2.3 Sinc Filter Synchronization
The sinc filter is synchronized to the external sys-
tem by the MSYNC signal, which is generated
from the SYNC input. The MSYNC signal sets a
reference time (time 0) for all filter operations, and
the sinc filter is restarted to phase align with this
reference time. See System Synchronizationon
page 77 for information about how the MSYNC
signal is generated.
During synchronization, the sinc filter resets all in-
ternal address pointers and restarts the filter on the
next data input. Existing data in the internal data
registers is not cleared, so immediately after syn-
chronization the data from the sinc filter will be a
combination of pre-sync and post-sync data.
8.3 FIR Filters
The finite impulse response (FIR) filter block con-
sists of two cascaded filters, FIR1 and FIR2, that
can each be programmed with a maximum of 255
coefficients. FIR coefficients in the CS5376 are 24-
bit 2s complement values normalized to
0x7FFFFF (decimal 8388607).
The programmed coefficients for the FIR filters are
completely arbitrary and can implement any type
of finite impulse response filter. Linear phase, min-
imum phase, phase compensation, or other com-
plex filter types can be used depending on the
application requirements. The ability to write and
re-write filter coefficients through the SPI 1 port
also allows quasi-adaptive filters, though updating
coefficients during operation without disrupting
the output data stream is not possible.
8.3.1 FIR1 Filter
The FIR1 filter stage has a decimate by 4 or 16 ar-
chitecture, and can be programmed with a maxi-
mum of 255 coefficients. The coefficients should
be normalized to 24-bit 2s complement full scale,
0x7FFFFF (decimal 8388607).
The characteristic equation for FIR1 is a convolu-
tion of the input values, X(n), and the filter coeffi-
cients, h(k), to produce an output value, Y.
Y = [h(k)*X(n-k)] + [h(k+1)*X(n-(k+1))] + ...
8.3.2 FIR2 Filter
The FIR2 filter stage has a decimate by 2 or 4 ar-
chitecture, and can be programmed with a maxi-
mum of 255 coefficients. The coefficients should
be normalized to 24-bit 2s complement full scale,
0x7FFFFF (decimal 8388607).
FIR1 Filter - decimate by 4, 16
FIR2 Filter - decimate by 2, 4
Figure 38. FIR Filters
DS256PP1
60

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