GC2011A datasheet(35/50 Pages) TI

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Texas Instruments Incorporated

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GC2011A 3.3V DIGITAL FILTER CHIP

SLWS129A

This document contains information which may be changed at any time without notice

6.2

A-PATH AND B-PATH CONTROL REGISTER 1

Control registers APATH_REG1 and BPATH_REG1 are identical and are described here.

ADDRESS 1:

APATH_REG1

ADDRESS 3:

BPATH_REG1

BIT

TYPE

NAME

DESCRIPTION

0-4 (LSBs)

R/W

FEED_BACK

This 5 bit field controls the symmetric filter feedback mode according to the

following table:

FEED_BACK

DESCRIPTION

(HEX)

no symmetry

full rate odd symmetry

full rate even symmetry and

A-path cascade mode

decimate and interpolate by 2 odd symmetry

decimate by 2 even symmetry and

decimate by 4 odd symmetry

decimate by 4 even symmetry and

half and quarter rate odd symmetry

half and quarter rate even symmetry

NOTE: the A-path FEED_BACK control must be 08 in the

cascade mode.

R/W

ANTI_SYM

Anti-symmetric filters can be implemented by setting this bit and the CIN

bit described below. This bit complements (bitwise inverts) the feedback

data.

EXCEPTION: In the cascade mode the A-PATH ANTI_SYM bit must be

set for all filters.

R/W

CIN

This is the carry input to the filter cell’s 12 bit adder (See Figure 5). This

bit is set to create anti-symmetric filters. In the cascade mode this bit is

cleared in both paths to create a symmetric filter and it is set in both paths

to create an anti-symmetric filter.

R/W

ODD_SYM

This bit must be set for odd-symmetry filters and cleared for even

or non symmetric filters.

8-12

R/W

REV_DELAY

These five bits control the filter cells’ reverse delays.

These bits are not used if FEED_BACK=00 (no symmetry)

REV_DELAY

DESCRIPTION

(HEX)

no symmetry

full rate filters

decimate by 4 and half rate filters

decimate and integrate by 2 filters

quarter rate filters

13-15(MSB)

R/W

FOR_DELAY

These 3 bits control the filter cells’ forward delays.

FOR_DELAY

DESCRIPTION

decimate and interpolate by 4 filters

decimate and interpolate by 2 filters

full rate filters

quarter rate filters

half rate filters

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