PBL38570 查看數據表（PDF） - Ericsson

零件编号

产品描述 (功能)

比赛名单

PBL38570

Universal Speech Circuit

Ericsson  

PBL 385 70

a)

Mute IMute

PBL

385 70

5

VMute

14

-L

b)

Mute IMute

PBL

385 70

5

VMute

14

-L

c)

PBL

385 70

14 5

-L

Mute

d)

PBL

385 70

17

Rx

18

15

Muting

points

The diode has to be low

voltage drop type.

Receiver mute only.

Figure 15. Mute principles.

Mute function

The circuit has a mute function at pin 5.

Sinking current from this pin will cut off the

gain in the microphone amplifier

(attenuation min. 60dB) and decrease the

gain in the receiver amplifier to reach the

confidence tone level at DTMF-dialling.

The receiver mute is ≈ 40dB down from the

unmuted value to satisfy those who keep

the handset close to the ear at dialling.

Optional conditions.

For users who keep the handset from

the ear the confidence tone level is too low.

To alter the level, a signal can be taken

from DTMF generator output to receiver

input before the capacitor C6. The added

impedance to this point will hardly disturbe

the signal condition in active speech mode.

The microphone amplifier only, can be

muted by sinking current from the output

pin 11. See fig.4 or 9.

Figure 15 b.) If the system mute signal

is used to other tasks than muting the

speech circuit it has to be isolated. If a

diode is used it has to be a low voltage drop

type. The input at mute has to be below

300mV. If the mute signal has reverse

polarity out of the system it can be phase

changed like in e.) In case it is required to

mute the receiver only, d.) it can be done

by shorting the receiver input to ground

before or after the input capacitor. Shorting

the input pin to ground (does not have to be

absolute ground) actuates a mute by driving

the amplifier into saturation thus blocking

the signal path and rendering a mute with

high attenuation but will cause a DC-level

shift at output which in its turn will cause a

”click ” in the earphone. This can be softe-

ned with a slower mute signal flank. If the

second approach, grounding before the

input capacitor is chosen, the grounding

has to be low ohmic in order to render a

high attenuating mute.

Start up circuit

The circuit contains a start up device

which function is to fast charge the

capacitor C1 when the circuit goes into

hook- off condition. The fast charge circuit

is a thyristor function between pins 1 and

4 that will stop conducting when the current

drain at pin 4 is lower than ≈ 700 µA + the

internal current consumption. ( about 1

mA) This circuit can not retrigger before

the voltage level at C1 drops below 2V or

the line voltage below 1V. See fig 16.

1

PBL 385 70

Tx

2

DC supply

4

+Line

R3

C1

-Line

Figure 16. Fast start up principle.

Power supplies DC1, DC2, V+C and

VPA(See fig.17)

PBL 38570 generates its own DC supply

V+C dependent of line current with an

internal shunt regulator. This regulator

senses the line voltage VL via R3 and line

current via R6 in order to set the correct

V+C so the circuit can generate the required

DC characteristic for a given line resistance

RLine and the line feeding data of the

exchange. A decoupling capacitor is

needed between pins +C and -L. The V+C

supply changes its voltage linearly with the

line current. It can be used to feed an

electret microphone. Caution must be ta-

ken though not to drain too much current

out of this output because it will affect the

internal quick start circuit by locking itself

into active state. (max. permissible current

drain 700µA).

Care has to be taken when deciding the

resistance value of R3. All resistances that

are applied from +Line to ground (-Line)

will be in parallel, forming the real

impedance towards the line. This will

sometimes result in, that the ohmic value

of R3 is increased in order to comply to the

impedance specification towards the line.

The speech circuit sinks ≈ 1mA into pin 4,

which means that the working voltage for

the speech function V+ will decrease with

increasing R3, thus starving in the end the

circuit of its working voltage . This

dependency is often falsely taken as a sign

of that the circuit does not work down to the

low line current specified, but in fact it is the

working voltage at pin 4 that has become

too low. It is obvious that this problem is

also connected into what kind of DC-

characteristic is set. See fig. 7.

10

Share Link: