NJW1124 datasheet(21/29 Pages) NJRC

21 / 29 page

NJW1124

– 21 –

7.2 Background Noise Monitor

Background Noise Monitor judges whether the input signal is noise or sound or voice by TLO2 and RLO2 voltage,

and change the mode.

The NJW1124 includes the Background noise monitor on transmit side and receive side.

Fig.10 shows Block diagram of Background noise monitor.

The voltage difference between TLO2 or RLO1 and Ref is amplified 8.6dB on AMP1.

The signal from AMP1 inputs 2

nd stage AMP2 and comparator (COMP).

The COMP non-inverting input voltage becoming 36mV higher than inverting, COMP output 1,which shows the

NJW1124 is transmit or receive mode.

At the same time, external capacitor charged from 0.8

µA internal current source, until the CCP voltage becomes

46mV higher than AMP2 input voltage.

The equivalent below shows CCP voltage charging.

∆VCCP= 0.8µA/CCP

For example, CCP=1µF, δVCP=0.8V/sec.

Without the input signal, C CP discharged and finally reset the Background noise monitor.

Response example is ex.3.

The signal like continued sign wave inputting, COMP output ‘0’ which is noise-monitoring mode (idle-mode).

The signal like conversation sound inputting, CCP continues to charge and discharge. COMP output continued

to ‘1’, which is transmit or receive mode.

Small Ccp shortens the time shifting to ‘0’ condition. Too small CCP attenuates even the conversation signal.

Large CCP keeps ‘1’ condition long, which lengthen attenuating time.

Capacitor should be adjusted appropriately on actual application.

(Use high input impedance like FET probe measuring voltage of CPT, CPR pin.)

Fig.8 Background Noise Monitor Block Diagram

800

850

900

950

1000

1050

1100

1150

1200

1250

1300

100

200

300

400

500

time [m sec]

TLO2

CPT

800

850

900

950

1000

1050

1100

1150

1200

1250

1300

1020

3040

time [m sec]

TLO2

CPT

Ref

Level

Detector

Tx : S3

Rx : S4

Tx : TLO2

Rx : RLO1

AMP1

AMP2

COMP

36mV

Tx : CPT

Rx : CPR

CCP

(C2,C22)

19kΩ

32kΩ

0.8

µµµµ A

46mV

Response example.3

TLO2 vs. CPT signal (input start)

MCO = 200mVrms/1kHz

C5 = 0.1

µF, C4=1µF

Response example.4

TLO2 vs. CPT signal (input finish)

MCO = 200mVrms/1kHz

C5 = 0.1

µF, C4=1µF

Function

recommendation value

Detail

Memo

Noise Detection

100nF～1

µF

The time for noise detection depends on this.

NJW1124 Datasheet(PDF) 21 Page - New Japan Radio

NJW1124 Datasheet(HTML) 21 Page - New Japan Radio

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Datasheet Download

Link URL