GC5318 Datasheet, PDF (13/45 Pages) Texas Instruments – HIGH-DENSITY DIGITAL UPCONVERTER

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GC5318
HIGH-DENSITY DIGITAL UPCONVERTER
SLWS187 – JULY 2006
Table 2-7. Programming
VARIABLE
crastsrttap_pfir(4:0)
cdma_mode
symmetric_pfir
DESCRIPTION
Number of DUC PFIR filter taps is (2 x crastarttap) + 1
When set, puts the CFIR and PFIR blocks in CDMA2000 mode.
Set to '1' if filter is symmetric. This value saves a modest amount of power.
The 18-bit PFIR filter coefficients are loaded by the software cmd5318. The user must provide a coefficient file
with one integer coefficient per line. Note that the PFIR filter coefficients are shared by the A and B signals in
CDMA mode.
2.1.5.2 Compensating FIR Filter
The CFIR filter interpolates by a fixed factor of two and is usually programmed to compensate for the CIC
filter roll-off.
The CFIR filter length is programmable. This programmable length permits turning off taps and saving
power if short filters are appropriate. The maximum CFIR filter length is a function of GC5318 clock rate
and input sample rate and is limited by the number of coefficient memory registers. The number of CFIR
taps in CDMA mode is 31 to 47, while in UMTS mode it is 15 to 31. In both cases, the number of taps is
one less than a multiple of four (31, 35, ... 59, 63).
Subject to the above minimum, maximum, and increment values, the maximum number of taps available
is:
• UMTS Mode: txclk × input sample rate
• CDMA Mode: 0.5 x (txclk × input sample rate)
For example, a txclk of 122.88 MHz in UMTS mode (at 3.84 MSPS) provides 31 taps, while CDMA
(1.2288 MSPS) mode provides 47 taps.
The CFIR coefficients are shared by the A and B signals in CDMA mode.
CFIR gain is:
Gain = sum(coefficients) x 2^cfir_gain-19
Table 2-8. Programming
VARIABLE
crastsrttap_cfir(4:0)
symmetric_cfir
cfir_gain
DESCRIPTION
These bits define the number of taps that CFIR uses for the filtering. DUC CFIR: (2 x crastarttap_cfir) +1.
Note: crastarttap_cfir must be odd.
Set to '1' if filter is symmetric. Saves a bit of power.
CFIR gain adjustment.
The 18-bit PFIR filter coefficients are loaded by the software cmd5318. The user must provide a coefficient file with
one integer coefficient per line. Note that the PFIR filter coefficients are shared by the A and B signals in CDMA
mode.
GC5318 Operation
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