U4091BM-RFNY19 Atmel, U4091BM-RFNY19 Datasheet - Page 28

• Manufacturer Part Number: U4091BM-RFNY19
• Description: RF Wireless Misc COM.CORDED - FEATURE PHONE CIRCUIT
• Manufacturer: Atmel
• Type: Programmable Telephone Audio Processorr

Specifications of U4091BM-RFNY19

• Operating Frequency: 100 KHz
• Operating Temperature Range: - 55 C to +150 C
• Package / Case: SSO-44
• Mounting Style: SMD/SMT

15. Sidetone System
Figure 15-1. Principle Circuit of Sidetone Balancing
28
Atmel U4091BM-R
LRX
AGARX
0 - 7 dB
The Sidetone Balancing (STB) has the task of reducing the cross-talk from LTX (microphone)
to LRX (earpiece) in the frequency range of 0.3kHz to 3.4kHz. The LTX signal is converted
into a current in the MOD block. This current is transformed into a voltage signal (LINE) by the
line impedance ZL. The LINE signal is fed into the summing amplifier DIFF1 via capacitor CK
and attenuator AMP1.
On the other hand the LTX buffered by STOAMP drives an external low-pass filter (RST,
CST). The external low-pass filter and the internal STB have the transfer function drawn in the
STB box. The amplified STB output signal drives the negative input of the summing block. If
both signals at the DIFF1 block are equal in level and phase, we have good suppression of the
LTX signal. In this condition, the frequency and phase response of the STB block will repre-
sent the frequency curve on line.
In real life, the line impedance ZL varies strongly for different users. To obtain good suppres-
sion with one application for all different line impedances, the STB function is programmable.
9 dB
STO_DIFF
-
+
AMP2
DIFF1
g
LF
LF
LTX
Sidetone balancing
-10 dB
P
P
AMP1
STOAMP
MOD
SL
SL
-10 dB
8 dB
f
RECIN
LINE
STRC
STO
STC
CK
33 nF
CTO
STO
8.2 kΩ
ZL
4872B–CORD–01/11