CSP1027 Datasheet, PDF (7/64 Pages) Agere Systems – CSP1027 Voice Band Codec for Cellular Handset and Modem Applications

Data Sheet
December 1999
CSP1027 Voice Band Codec for
Cellular Handset and Modem Applications
4 Architectural Information (continued)
Following the low-pass filtering and decimation to 8 kHz, the 16-bit two's complement PCM can go directly to the
output register, cdx(A/D), or go to a third-order IIR digital high-pass filter and then to the output register. The –3 dB
corner frequency of the high-pass filter is approximately 270 Hz. This filter exceeds the VSELP preprocessing
requirements of IS-54 for attenuation of 60 Hz and 120 Hz signals. The high-pass filter is selected by writing the
HPFE field in the cioc3 register (see Table 10 on page 29). The default value upon reset is the high-pass filter
enabled (HPFE = 0).
Vin1
Vin2
Cin
MICIN
Cin
AUXIN
Rin
Rin
PREAMPLIFIER
AND AA-FILTER
+ _A/D
AND
FILTERS
–
EXTERNAL
COMPONENTS
Figure 4. CSP1027 A/D Path When in the Preamplifier Mode (EIGS = 0)
5-7592 (F)
AUXIN
Cfb
Rfb
Cin Rin
MICIN
EXTERNAL
COMPONENTS
INTERNAL
SIGNAL GND
–
+
INTERNAL
SIGNAL GND
+ _A/D
AND
FILTERS
–
Figure 5. CSP1027 A/D Path in the External Gain Select Mode (EIGS = 1)
5-7593 (F)
4.2.5 A/D Path Frequency Response
The composite digital filters (decimator, LPF, and HPF)
meet the ITU-T G.712 voice band frequency response
specifications and are suitable for IS-54, JDC, and
GSM digital cellular applications. Figures 6 through 9
show the A/D and D/A frequency response without the
optional high-pass filter (HPF). Figures 10 and 11 show
the group delay characteristics of the A/D and D/A with-
out the high-pass filter. Figures 12 and 13 show the fre-
quency response of the high-pass filter. Figures 14 and
15 show the group delay characteristics of the high-
pass filter. In all figures, the frequency is normalized to
the sampling frequency fS (i.e., frequency/fS). To get the
actual frequency, multiply the normalized frequency by
fS. The absolute delay and delay distortion have been
normalized to the sampling period 1/fS (i.e., delay x fS).
To obtain the actual delay, divide the normalized delay
by fS. The templates shown in Figures 7 through 9,
11 through 13, and 15 correspond to the limits in the
ITU-T G.712 specification where fS = 8.0 kHz.
4.2.6 PCM Saturation Versus Analog Input Levels
16-bit two's complement saturation is employed to pre-
vent wraparound during input overload conditions. The
saturation is hard-limiting:
0x7fff = maximum positive level
0x8000 = minimum negative level
The analog levels that correspond to the saturation lev-
els for the three input modes are outlined in Table 14 on
page 51.
Lucent Technologies Inc.
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