BL34118
Voice Switched Speakerphone Circuit BL34118
The BL34118 Voice Switched Speakerphone Circuit incorporates the necessary amplifiers,
attenuators, level detectors, and control algorithm to form the heart of a high quality hands-free
speakerphone system. Included are a microphone amplifier with adjustable gain and MUTE control,
Transmit and Receive attenuators which operate in a complementary manner, level detectors at both
input and output of both attenuators, and background noise monitors for both the transmit and receive
channels. A Dial Tone Detector prevents the dial tone from being attenuated by the Receive background
noise monitor circuit. Also included are two line driver amplifiers, which can be used to form a hybrid
network in conjunction with an external coupling transformer. A high-pass filter can be used to filter out
60Hz noise in the receive channel, or for other functions. A chip Disable pin permits powering down the
entire circuit to conserve power on long loops where loop current is at a minimum.
The BL34118 may be operated from a power supply, or it can be powered from the telephone line,
requiring typically 5.0 mA. The BL34118 can be interfaced directly to Tip and Ring (through a coupling
transformer) for stand-alone operation, or it can be used in conjunction with a handset speech network
and/or other features of a feature phone.
Improved Attenuator Gain Range: 52 dB Between Transmit and Receive
Low Voltage Operation for Line-Powered Applications (3.0 鈥?6.5V)
4-Point Signal Sensing for Improved Sensitivity
Background Noise Monitors for Both Transmit and Receive Paths
Microphone Amplifier Gain Set by External Resistors 鈥?Mute Function Included
Chip Disable for Active/Standby Operation
On Board Filter Pinned-Out for User Defined Function
Dial Tone Detector to Inhibit Receive Idle Mode During Dial Tone Presence
Standard 28-Pin Plastic DIP Package and SOIC Package Available
Compatible with BL34119 Speaker Amplifier
PIN CONNECTIONS( Top View )
FO
FI
CD
Vcc
HTO+
HTO-
HTI
TXO
TXI
MCO
MCI
MUT
VLC
CT
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2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
CPR
RLI1
RLO1
TLO1
TLI1
RXO
RXI
RLI2
RLO2
TLO2
TLI2
CPT
VB
http://www.belling.com.cn
-1-
8/15/2006
Wrote by 2006
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