U4087B

Preliminary Information

TELEFUNKEN Semiconductors

Rev. A1, 09-Sep-96

1 (8)

Low Voltage Voice Switch Interface Circuit for Hands-free

Operation in Telephone

Description

The voice switch interface circuit U4087B is a linear

integrated

circuit

for

improvement

of

handsfree

performance of U4090B system.

The U4087B provides an optimized interface to U4090B,

the necessary level detectors and switching control for a

properly

operating

speakerphone.

The

detection

sensitivity and timing are externally controllable.

Additionally, the U4087B provides a back- ground noise

monitor which makes the circuit insensitive to room

noise.

The Block diagram shows level detectors, back ground

noise monitor.

Due to low voltage operation it can be operated via power

supply management of U4090B requiring 1.0 mA typ.

Features

D Low voltage operation: 3.0 to 7.0 V

D Four point signal sensing

D Monitoring system for background noise level

D Case: SO 16

D Chip Disable for active/standby operation

Benefits

D Fast channel switching allows quasi duplex operation

D Low current consumption

Block Diagram

Bias

Noise

detector

713

6

5

TS

–

+

=

14

+

–

Logic

15

Logic

16

C.T.

Generator

Charge

DIRA

Discharge

Logic

9

–

+

DIRE

2

Logic

Logic

1

4

10

11

12

CT

8

12610

TLO2

CPT

VB

VM

CD GND

TLO1

TLI1

RLI1

3

TLDR

TLDT

RLO1

RLO2

RLI2

TLI2

Figure 1. Block diagram with external circuit