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NJW1124

Voice Switched Speakerphone circuit

Japan Radio Corporation  

NJW1124

■APPLICATION NOTES

■GENERAL DESCRIPTION

The NJW1124 is a Voice Switched Speakerphone Circuit. The NJW1124 includes all of functions

processing a high quality hands–free speakerphone system, such as the necessary amplifiers

( Microphone amplifier , Receive amplifier, Line amplifier), attenuators, level detectors .

All external capacitors are sufficient small so that ceramic capacitors are applied.

The NJW1124 detects a signal to judges which path is talking. After that, the one side path is

active, another path is attenuated. This is half-duplex system. Appropriate operating keeps closed loop

gain less than 0dB, and that prevents acoustic coupling.

The resister and capacitor values in Fig.1 below are references. For correct operating, check in

actual condition as possible as you can. And adjust the levels input each detectors.

On this application notes, Base unit is defined as the unit included the NJW1124.

MUT

V+

GN D

Microphone

C6 R2

100n 5.1k

R3

C7

51k

100n

M CI

M CO

R4

51k

TLI2

C8 C9 R6

100n 100n 5.1k

R5

10k

TLI1 TXO

LII

R7

51k

C10

LiO-

LiO+

:MU TE

:ACTIVE

V+

R1

300k

C1

1µ

C3

470n

C4

470n

C2

1u

M UT

TLO2

RLO2

CPT

VREF

Mic

Amplifier

Tx Attenuator

Lev el

Detector

Background

NoiseMonitor

Attenuator

Control

VREF

-1

Line Amplifier

Background

NoiseMonitor

Lev el

Detector

C 23

1µ

VREF

VREF2

BIAS

IC1

NJW1124

Rx Attenuator

1.2µ A

Receive

Amplifier

VREF

Line Out

V+

C11

V+

1µ

M onitor

CT

RTSW

C5

1µ

V+

C22

CPR

1µ

TLO1

RLO1

C20

470n

C21

470n

V+ :Recive

GND :Trensmit

Open :idle

GND

MU T

V+

GND

: Active

: Disable

V+

R10

15k

C15

1µ

Speaker

IC2

NJU7084

Power Amplifier

5.0V

+ C16

10µ C13

1µ

C14 1 µ

R9

22k

RXO RLI2

R11

C17 10k

100n

R8 C12

11k 100n

VLC

R12

51k

RVLC

RLI1 FO

C 18

100n

R13

5.1k

FI

R14 C19

5.1k 100n

Recive In

Fig.1 NJW1124 Block Diagram

The resistance and capacitor value above is just one example.

Certain Half-duplex operation are not guaranteed.

Best value depends on your microphone, speaker, and chassis.

Especially, select capacitor value connected to V+(17pin) to be power

supply ripple enough small (less than 5mVp-p).

when 1µF is not enough, select larger value capacitor.

– 13 –

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