GC2011A datasheet(22/50 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

3.6

INTERPOLATION

Another common filtering application is to increase the signal’s sample rate through interpolation. Interpolation

is performed by inserting zeros between input samples so as to double or quadruple the sample rate, and then to low

pass filter the result. In the interpolation modes the GC2011A chip automatically zero pads the input as it low pass filters

the result. The interpolation modes double or quadruple the number of taps implemented by each filter cell. The input

sample rate is one half or one fourth the clock rate as shown in Figure 6. The output rate is at the clock rate.

In the interpolate by 4 (quarter rate in, full rate out) mode the coefficient storage is reversed within each filter

cell. The interpolate by 4 coefficients, h(k), are stored in:

memory address BASE+k+0 if k modulo-4 is 0

memory address BASE+k+2 if k modulo-4 is 1

memory address BASE+k+0 if k modulo-4 is 2

memory address BASE+k-2 if k modulo-4 is 3

where BASE is 128 for A-path or cascaded filters and is 192 for B-path filters. For example,

Coefficient Memory address

h(0)

128+0

h(1)

128+3

h(2)

128+2

h(3)

128+1

h(4)

128+4

h(5)

128+7

h(6)

128+6

h(7)

128+5

h(8)

128+8

h(9)

128+11

etc.

Table 7: Interpolation Mode Control Register Settings

I/O Rates

Symmetr

Dual Path or

Cascaded

# of Taps

(N)

A-PATH

B-PATH

Cascade

Latency

Tap

Storagea

a. HR = Use half rate coefficient storage as described in Section 3.2. DF = Use double to full rate storage in Section 3.8.

Out

REG0 REG1 REG0 REG1

REG

Full

Double

Odd

Dual

20D8

6108

20D8

6181

2000

Half

Full

None

Dual

6388

2E00

4388

2E00

2000

Cascaded

6388

2E28

4388

2E00

5E00

Odd

Dual

6388

2E91

4388

2E91

2000

Cascaded

127

6388

2EA8

4388

2E91

5E00

Quar-

ter

Full

None

Dual

A200

0000

8200

0000

2000

See

Text

Cascaded

128

A200

0028

9200

0000

5E00

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