GC5316 datasheet(34/75 Pages) TI

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GC5316

SLWS154A − JANUARY 2004 − REVISED MARCH 2004

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Table 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 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.

3.1.5.3

Transmit CIC Filter

Out

−m1

−1

Zero Pad

by 3−31

−1

Shift

0− 31

Round

Shift

−m2

−m3

−m4

−m5

−1

m1, m2, m3, m4, m5, m6 = 1 or 2

−m6

Force 0

Figure 28. Transmit CIC Filter

The transmit six stage CIC filter interpolates over a programmable range from 4 to 32. The filter is made up of six

banks of 24-bit subtractor sections followed by six banks of integrator sections. Each of the six subtractor sections

can be independently programmed with a differential delay of one or two. A shift block follows the last integration stage

and can shift the 50-bit accumulated data down by 31−TCIC_SHIFT bits yielding 18-bit output data.

The CIC filter exhibits a droop across its frequency response. Usually the preceding CFIR filter precompensates for

the CIC droop with a gradually rising frequency response. However, it is also possible to provide the precompensation

in the PFIR filter.

CIC interpolation filters can become unstable if an external event (such as a cosmic particle) disturbs a storage node

in the CIC integrator section. This can add a bias which subsequently integrates out of control. The GC5316 transmit

CIC employs a patented method to detect and then automatically flush and reset the filter. Register bits are available

to disable and to test this auto-flush feature. A maskable interrupt becomes active if a CIC error occurred.

The gain of the CIC filter is: Ncic5 x 2(number ofstages where M=2) x 2(CIC_SCALE − 31) where CIC_SCALE is 0 to 31. Ncic

is the interpolation ratio and is programmed as cic_interp_decim + 1.

Since the CIC output is full rate for both UMTS and CDMA, a complete hardware path is required for each of the

signals A and B from this point on in the transmit signal path. For CDMA, there are four independent CIC filters (I/Q

for signal A and I/Q for signal B). For UMTS, the two signal B CIC filters are disabled.

GC5316 Datasheet(PDF) 34 Page - Texas Instruments

GC5316 Datasheet(HTML) 34 Page - Texas Instruments

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