CSP1027 datasheet(46/64 Pages) AGERE

46 / 64 page

CSP1027 Voice Band Codec for

Data Sheet

Cellular Handset and Modem Applications

December 1999

Lucent Technologies Inc.

7 Application Information (continued)

7.5.4 Enhanced Oversampling Clock Generation

If system constraints make the requirement of integer

multiples of 125 x the sampling rate (typically integer

multiples of 1.0 MHz) difficult to provide, the CSP1027

can also operate with the ICLK0 internal clock rate at

integer multiples of the sampling rate (typically integer

multiples of 8 kHz). See Section 4.5 on page 16 for

more information.

The following two examples illustrate the usage:

Application Example 4

Standard codec application.

CLK input clock rate: 2.048 MHz.

Codec sampling rate, fS: 8 kHz.

Solution:

CKOS = 125 x 8 kHz = 1.0 MHz, so CLK/CKOS =

2.048 or CLK/CKS = 2.048 x 125 = 256. Values of M

and N must be found to satisfy this requirement, as

shown below.

Set CDIV0 for ÷1 (CDIV0 = 0); hence, fICLK = fCLK.

Using the equations from Section 4.5 on page 16,

Hence, M = 2, S = 1, and N = 6. (Note that if CDIV0

set for ÷ 2, then M = 1, S = +1, and N = 3, which is

not allowed.)

Using Tables 2 through 4 on page 18:

CDIV3 = 00 0010.

CDIFS = 0.

CDIF0 = 01 0101.

CDIF1 = 10 0110.

CDIF2 = 0 0000.

Application Example 5

IS-54 application.

Codec sampling rate, fS: 8 kHz.

CLK needs to be a common multiple of 8 kHz and

48 x 48.6 kHz.

Need phase adjustment.

Solution:

48 x 48.6 = 2.3328E6

2.3328E6 ÷ 8E3 = 291.6

To get a common multiple, 291.6 must be multiplied

by a factor to become an integer: 291.6 x 10 = 2916

(an integer). So, CLK/CKS = 2916 and CLK/ICLK0 =

2 CLK = 2916 x 8E3 = 23.328E6.

CLK input clock rate: 23.328 MHz.

Set CDIV0 for ÷2 (CDIV0 = 1) to allow advance/

retard for phase adjustment.

ICLK0 internal clock rate is 11.664 MHz.

Using the equations from Section 4.5 on page 16,

Hence, M = 12, S = –1, and N = 42.

Using Tables 2 through 4 on page 18:

CDIV3 = 00 1100.

CDIFS = 1.

CDIF0 = 00 0011.

CDIF1 = 11 0110.

CDIF2 = 0 0000.

FICLK0

-----------------

125

()

FICLK0

-----------------

2.048 MHz

8 kHz

------------------------------

256

125

()

FICLK0

-----------------

11.664 MHz

8 kHz

---------------------------------

1458

125

()

–

()

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