u4091bm-r ATMEL Corporation, u4091bm-r Datasheet - Page 16

• Manufacturer Part Number: u4091bm-r
• Description: Programmable Telephone Audio Processor
• Manufacturer: ATMEL Corporation

12. Acoustic Feedback Suppression
Figure 12-1. Basic System Configurations
16
U4091BM-R
MICRO
INLDT
CTU
RTU
MICO
LOG
Acoustical feedback from the loudspeaker to the hands-free microphone may cause instability of
the system. The U4091BM-R has a very efficient feedback-suppression circuit which offers a
4-point or (alternatively) a 2-point signal-sensing topology (see
Two attenuators (TXA and SAI) reduce the critical loop gain via the serial bus either in the trans-
mit or in the receive path. The overall loop gain remains constant under all operating conditions.
The LOGs produce a logarithmically-compressed signal of the TX- and RX-envelope curve. The
AFSCON block determines whether the TX or the RX signal has to be attenuated.
The voice-switch topology can be selected by the serial bus. In 2-point-sensing mode, AFSCON
is controlled directly by the LOG outputs.
SA
TLDT
CTLO
CBNMT
BNMT
CALCR
LOG
BNM
AFSCON
TXA
SAI
control
Mode
CCT
CT
DTD
CALCT
CBNMR
LOG
BNMR
BNM
TLDR
CRLO
AGATX
LOG
CRU
RRU
Figure
RECO2
RECO1
INLDR
12-1).
AGARX
HV
4872A–CORD–08/05
STO
Line