GC5316 datasheet(33/75 Pages) TI

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GC5316

SLWS154A − JANUARY 2004 − REVISED MARCH 2004

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3.1.5.1

Transmit Programmable FIR Filter

The transmit programmable FIR filter (PFIR) pulse shapes the baseband signal data and interpolates by a fixed factor

of two.

The PFIR length is programmable. This permits turning off taps and saving power if short filters are appropriate. The

maximum PFIR filter length is a function of GC5316 clock rate and input sample rate and is limited by the number

of coefficient memory registers. The number of taps available ranges in CDMA mode ranges from 31 to 63, in UMTS

mode it ranges from 15 to 63. Both in increments of four taps.

Subject to the above range, the maximum number of taps available is:

D UMTS Mode: 2 x ( txclk ÷ input sample rate)

D CDMA Mode: txclk ÷ input sample rate

Assuming a txclk of 122.88 MHz, both UMTS (3.84 MSPS) and CDMA (1.2288 MSPS) modes provide 63 taps. The

same PFIR coefficients are used for both the A and B signals in CDMA mode.

The PFIR filter consists of 32 forward and reverse data RAM cells each 36 bits in width. The coefficient memory

provides storage for up to 63 unique 18-bit taps. A 19 x 18 multiplier and full-precision accumulator form the filter

convolution. An optional (pfir_gain) up-shift of one follows. Finally, the output is hard-limited. The PFIR gain is:

Gain = sum(coefficients) x 2pfir_gain − 18

Table 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 saves a modest amount of power.

The PFIR filter’s 18-bit coefficients are loaded by the software cmd5316. 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.

3.1.5.2

Transmit Compensating FIR filter

The transmit CFIR filter interpolates by a fixed factor of two and is usually programmed to compensate for the CIC

filter’s roll-off.

The CFIR filter length is programmable. This permits turning off taps and saving power if short filters are appropriate.

The maximum CFIR filter length is a function of GC5316 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. The number of taps may be increased in increments of four taps.

Subject to the above minimum, maximum, and increment values, the maximum number of taps available is:

D UMTS Mode: txclk ÷ input sample rate

D CDMA Mode: 0.5 x (txclk ÷ input sample rate)

Assuming a txclk of 122.88 MHz, UMTS (at 3.84 MSPS) mode would provide 31 taps and 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 2cfir_gain−19

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