PSB21383H Datasheet, PDF (149/270 Pages) Infineon Technologies AG – Siemens Codec with S/T Transceiver

PSB 21381/2
PSB 21383/4
Description of the programmable speech detector parameters:
Codec
Parameter
LP1
OFF
PDS
PDN
LP2S
LP2N
LP2L
LIMX, LIMR
# of CRAM
Bytes
1
1
1
1
1
1
1
1
Range
1 to 512 ms
0 to 50 dB
1 to 512 ms
1 to 512 ms
4 to 2000 ms
1 to 512 ms
0 to 95 dB
– 36 to – 78 dB
Comment
Time constant LP1
Level offset up to detected noise
Time constant PD (signal)
Time constant PD (noise)
Time constant LP2 (signal)
Time constant LP2 (noise)
Limitation of LP2, related to LIM
Limitation of logarithmic amplifier
4.4.4 Speech Comparators (SC)
Switching from one active mode to another one is controlled by the speech comparators,
provided the speech detectors are indicating speech. There are two speech
comparators, one at the acoustic (AE) and one at the line side (LE). These comparators
continuously compare the signal levels of both signal paths and control the effect of the
echoes at the acoustic side and the line side. Once speech activity has been detected,
the comparator switches at once in that direction in which the speech signal is stronger.
For this purpose each signal is compared to the sum of the other and the returned echo.
4.4.4.1 Speech Comparator at the Acoustic Side (SCAE)
In principle, the SCAE works according to the following equation:
if SX > SR + VAE then TX
else RX
Being in RX-mode, the speech comparator at the acoustic side controls the switching to
TX-mode. Only if the SX-signal is higher than the SR-signal plus the expected/measured
acoustic level enhancement (VAE), the comparator switches immediately to TX-mode.
Physically the level enhancement (VAE) is divided into two parts: GAE and GDAE.
Data Sheet
139
2001-03-12