PBL38812 Ver la hoja de datos (PDF) - Ericsson

Número de pieza

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Fabricante

PBL38812

Voice-switch circuit for Handsfree speakerphone TAM

Ericsson  

PBL 388 12

dB Transmit

gain = ____

40

30

VCTR=V+

20

10

0

VCTR=open

-60

-40

VCTR = VREF

-20

0

20

Receive

dB

gain = ---------

30

20

VCTR=V+ 10

0

-10

VCTR=open -20

VCMP -V REF

40

60

mV

Figure 11. Transmit and receive gain as a function of VCMP and VCTR.

Rxdet

Txdet

A

B

CMP

E

F

Full recieve level

G

C

D

Full transmit level

Figure 12. Timing of the transmitter and receiver channels at the CMP-input.

Mode

Vref

25 dB speech

control

50 dB speech

control

DTMFMute

Total mute

VCTR

0

1

2

3

(V)

Figure 13. Control modes as function of voltage applied to gain dynamics control

input CTR; ID=1mA.

the transmitter channel and decrease it in

the receiver channel. Signal at Rxin will

do vice versa. The voltages RxDetout and

TxDetout control thus the gain setting in

respective channel through the

comparators using the CMP input as a

summing point with an input current of

less than 1µA. The attack and decay times

for the signals RxDetout and TxDetout are

controlled by individual external RC-

networks. The attack time in the receiver

channel is set by C2 together with C1 and

either by the maximum current capability

of the detector output or it with R2 added.

The transmitter channel works likewise.

See fig. 7.

The decay time in the receiver and trans-

mitter channels is set by C2 and C3

respectively. The resistor in the time cons-

tant is formed by an internal 200kΩ resistor

in parallel with the external resistors R3

and R4 respectively. The influence of

eventual R1 and R2 can be omitted.

The text above describes the case when

only one channel is open at a time and

there is a distinctive pause between sign-

als at receiver and transmitter channel

inputs so the circuit will have time to reach

its idle state. See fig.14 A) to E). If one of

the channels gets an input signal

immediately after the signal has

disappeared from the other channel input

the effective decay time, as the CMP in-

put sees it, will be shorter than in the first

case. See fig.14 F) to G). The capacitor

C4 at CMP - input sets the speed of the

gain change in the transmitter and recei-

ver channels. The capacitors C2 and C3

should be dimensioned for a charging time

of 0.5 - 10mS and for a discharge time of

150 - 300 mS. The question of switching

times being a highly subjective proposi-

tion, is in large dependent of the language

being spoken in the system, caused by

the varying sound pressure picture of the

different languagues. A hysteresis effect

is achieved in the switching since the level

detectors sense the signals after F2 and

F5 respectively (F2 and F5 are affected

by the gain setting). For example: If the

transmitter channel is open (maximum

gain), a smaller signal at Txin is enough

to keep the channel open than would

benecessary to open it when the receiver

channel is open. The output swing of the

level detectors is matched for variations in

the supply voltage. The detectors have

8

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