CSP1027 datasheet(45/64 Pages) AGERE

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Lucent Technologies Inc.

Data Sheet

CSP1027 Voice Band Codec for

December 1999

Cellular Handset and Modem Applications

7 Application Information (continued)

Thus, the contributions to frequency variation add up

as follows:

Initial Tolerance of Crystal

10.0 ppm

Temperature Tolerance of Crystal

25.0 ppm

Aging Tolerance of Crystal

6.0 ppm

Load Capacitor Variation

4.7 ppm

CSP1027 Circuit Variation

15.5 ppm

C0 Variation

7.8 ppm

Board Variation

23.3 ppm

Total

92.3 ppm

This type of detailed analysis should be performed for

any crystal-based application where frequency accu-

racy is critical.

7.5 Programmable Clock Generation

Refer to Figure 17 on page 15 for the following discus-

sion.

The programmable clock divider is set by writing the

6-bit CDIV3 field of the cioc2 register (see Table 9 on

page 28). The user can select an appropriate integer

value which sets the ratio of the CLK input clock to the

oversampling rate of the codec. The following examples

illustrate this feature.

7.5.1 Application Example 1

GSM application.

Input clock, CLK, rate: 26 MHz (38.46 ns).

Codec PCM rate required: 8 kHz (oversampling

rate = 1 MHz).

Solution:

CLK/CKOS = 26, so set CLK/ICLK0 = 1 and ICLK0/

CKOS to 26.

Set CDIV0 = 0 and CDIV3 = 26 (011010).

7.5.2 Application Example 2

IS-54 application.

Input clock, CLK, rate: 40 MHz (25.0 ns).

Codec PCM rate required: 8 kHz (oversampling

rate = 1 MHz).

Solution:

CLK/CKOS = 40, so set CLK/ICLK0 = 1 and ICLK0/

CKOS to 40.

Set CDIV0 = 0 and CDIV3 = 40 (101000).

7.5.3 Application Example 3

Modem data pump.

Codec sampling frequency required = 9.6 kHz

(instead of 8 kHz).

Need highest possible input clock, CLK, rate (allow-

able by the DSP).

Solution:

Codec oversampling rate = 9.6 kHz * 125 = 1.2 MHz.

Assuming a DSP16A or DSP1616 with

maximum rate of 40 MHz,

CLK = 39.6 MHz = 1.2 MHz x 33, so

CLK/ICLK0 = 1 and ICLK0/CKOS = 33.

Set CDIV0 = 0 and CDIV3 = 33 (100001).

Disable the high-pass filters (HPFE = 1) because the

–3 dB corner frequency is now too high

(270 Hz x 1.2 = 324 Hz).

Low-pass filter –3 dB corner frequency is now

4.08 kHz (= 3.4 kHz x 1.2). (Note that external DSP

software can provide additional postfiltering, if

desired.)

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