CSP1027 Datasheet, PDF (46/64 Pages) Agere Systems – CSP1027 Voice Band Codec for Cellular Handset and Modem Applications

CSP1027 Voice Band Codec for
Cellular Handset and Modem Applications
Data Sheet
December 1999
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
s Standard codec application.
s CLK input clock rate: 2.048 MHz.
s Codec sampling rate, fS: 8 kHz.
Solution:
s 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.
s Set CDIV0 for ÷1 (CDIV0 = 0); hence, fICLK = fCLK.
s Using the equations from Section 4.5 on page 16,
-^F---^I--^C---^L---^K---⁰- = (125 × M) + (S × 2)
FS
-^F---^I--^C---^L---^K---⁰- = -²---^.-⁰----⁴---⁸------^M-----^H-----^z- = 256 = (125 × 2) + (1 × 6)
FS
8 kHz
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.)
s 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
s IS-54 application.
s Codec sampling rate, fS: 8 kHz.
s CLK needs to be a common multiple of 8 kHz and
48 x 48.6 kHz.
s Need phase adjustment.
Solution:
s 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.
s CLK input clock rate: 23.328 MHz.
s Set CDIV0 for ÷2 (CDIV0 = 1) to allow advance/
retard for phase adjustment.
s ICLK0 internal clock rate is 11.664 MHz.
s Using the equations from Section 4.5 on page 16,
-^F---^I--^C---^L---^K---⁰- = ¹----¹---^.--⁶---⁶---⁴------^M-----^H-----^z-- = 1458 = (125 × 12) + (–1 × 42)
FS
8 kHz
Hence, M = 12, S = –1, and N = 42.
s Using Tables 2 through 4 on page 18:
CDIV3 = 00 1100.
CDIFS = 1.
CDIF0 = 00 0011.
CDIF1 = 11 0110.
CDIF2 = 0 0000.
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Lucent Technologies Inc.