GC5316 Datasheet, PDF (17/75 Pages) Texas Instruments – HIGH-DENSITY DIGITAL DOWNCONVERTER AND UPCONVERTER

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From CF IR
P FIR
First Half Coefficients
Tap Delay
GC5316
SLWS154A − JANUARY 2004 − REVISED MARCH 2004
C0
DDC 2K
CN _{/2 −1}
PFIR
Second Half Coefficients
Tap Delay
DDC 2K+1
CN _/2
C _{N −1}
Figure 14. Double Tap Mode Interconnect
When in double-tap mode, the first half of the coefficients should be loaded into the even DDC, the remaining
coefficients go into the odd DDC. The even DDC must be turned on (ddc_duc_ena 1), and the odd DDC must be
turned off (ddc_duc_ena 0).
For strapped UMTS with double length filters, the range of taps available is 56 to 128 in increments of eight.
PFIR coefficients and gain shift values are shared between both A and B CDMA channels in a DDC block. The
number of maximum taps available for double length UMTS mode is:
Double Length UMTS Mode: 8 x (rxclk ÷ output sample rate)
VARIABLE
crastsrttap_pfir(3:0)
pfir_gain(2:0)
double_tap
Table 16. Programming
DESCRIPTION
Number of DDC PFIR filter taps is 4(crastartap+1)
For double-length PFIR the number of taps is 8(crastartap+1)
Sets the gain of the PFIR filter.
When set, puts two adjacent DDC (2k and 2k+1, k = 0 to 5) in 127 tap UMTS mode.
Set to 0 for normal mode.
Set to 2 for the main (even) DDC
Set to 1 for the secondary (odd) DDC.
When in double tap mode, the first half of the coefficients should be loaded into the even DDC, the
remaining coefficients go into the odd DDC.
ALSO: In double tap mode, the even DDC must be turned on (ddc_duc_ena 1), and the odd DDC
must be turned off (ddc_duc_ena 0).
The PFIR filter’s 18-one integer coefficient per line. Note that the PFIR filter coefficients are shared
by the A and B channels in CDMA mode.
Note: that the above PFIR filter coefficients are shared between both A and B sides of a DDC block.
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