GC2011A Datasheet, PDF (25/50 Pages) Texas Instruments – 3.3V DIGITAL FILTER CHIP

GC2011A 3.3V DIGITAL FILTER CHIP
SLWS129A
3.9 COMPLEX TO REAL QUADRATURE UPCONVERT
Complex data can be converted to real data by doubling the sample rate, mixing the data up by F_S/4 and saving
the real part. The control settings for this mode are shown in Table 9.
Table 10: Complex To Real Conversion Mode Control Register Settings
I/O Rates
In
Out
Symmetr
y
# of Taps
(N)
A-PATH
REG0 REG1
B-PATH
REG0 REG1
Cascade
REG
Output
REG
Latency
Full Double Odd
Half Full
Quar- Half
ter
63
20D8 6108 00D8 6181 2000 0001
44
127 638B A218 438B A294 2000 0012
46
255 A202 9018 8202 9094 2000 0033
50
The filter is an interpolate by two low pass filter with a pass band from 0 to F_S/4 and a stop band from F_S/4 to
F_S/2, where F_S is the output sample rate. The even coefficients of the filter are stored in the A-path filter cells and the
odd-coefficients are stored in the B-path filter cells. The real half of the complex samples are input as A-in, and the
imaginary half are input as B-in. The real results are output as A-out in all modes except for the double rate output mode.
In the double rate output mode the even time samples are output as A-out and the odd time samples are output as B-out.
In the full rate in to double rate out mode the coefficients h(k) are stored in register 1 of each filter cell. In this
mode store h(k) in addresses:
128+2*k+1
for k even, and
192+2*k-1
for k odd,
where k ranges from 0 to 31. h(31) is the center tap.
In the half rate in to full rate out mode the coefficients are stored in registers 0 and 1 of each filter cell. In this
mode store h(k) in addresses:
128+k
for k modulo 4 = 0
192+k-1
for k modulo 4 = 1
128+k-1
for k modulo 4 = 2
192+k-2
for k modulo 4 = 3
where k ranges from 0 to 63. h(63) is the center tap.
In the quarter rate in to half rate out mode the coefficients are stored in registers 0, 1, 2 and 3 of each filter cell.
In this mode store h(k) in addresses:
128+k/2
for k even
192+(k-1)/2
for k odd
where k ranges from 0 to 127. h(127) is the center tap.
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