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GC5318

HIGH-DENSITY DIGITAL UPCONVERTER

SLWS187 – JULY 2006

Table 2-7. Programming

VARIABLE

DESCRIPTION

crastsrttap_pfir(4:0)

Number of DUC PFIR filter taps is (2 x crastarttap) + 1

cdma_mode

When set, puts the CFIR and PFIR blocks in CDMA2000 mode.

symmetric_pfir

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:

Table 2-8. Programming

VARIABLE

DESCRIPTION

crastsrttap_cfir(4:0)

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.

symmetric_cfir

Set to '1' if filter is symmetric. Saves a bit of power.

cfir_gain

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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