PBL38570 データシートの表示（PDF） - Ericsson

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PBL38570

Universal Speech Circuit

Ericsson  

PBL 385 70

DC - characteristic

The DC - characteristic that a telephone

set has to fulfill is mainly given by the

network administrator.Following para-

meters are useful to know when the DC

behaviour of the telephone is to be set:

The voltage of the feeding system.

The line feeding resistance 2x... ohms.

The maximum current from the line at

zero line length.

The min. current at which the telephone

has to work (basic function).

The lowest and highest voltage

permissible across the telephone set.

The highest voltage that the telephone

may have at different line currents is

normally set by the network owners

specification. The lowest voltage for the

telephone is normally set by the voltages

that are needed for the different parts of

the telephone to function. For ex. for trans-

mitter output amplifier, receiver output

amplifier, dialler, speech switching and

loudspeaker amplifier in a handsfree

telephone etc.

R6 will set the slope of the DC-char. and

the rest of the level is set by some constants

in the circuit as shown in the equation

below. The slope of the DC-char. will also

influence the line length regulation (when

used ) and thus the gain of both transmitter

and receiver. See the table under gain

regulation.

VLine ≈ 2 + 1. 5 ⋅R 6 ⋅Iline

Vtelephoneline ≈ 1. 5V + Vline

Microphone amplifier

The microphone amplifier in PBL38570

is divided into two stages. The first stage is

a true differential amplifier providing high

CMRR (-55 to -65 dB typical) with voltage

gain of 19 dB. This stage is followed by a

gain regulated amplifier with a regulation

range of 5 ± 2 dB. The input of the

microphone amplifier can be used for

dynamic or electret transducers.

See fig. 8.

An electret microphone with a built in

FET amplifier is to be seen from outside as

a high impedance constant current gene-

rator and is normally specified with a load

resistance of ≈ 2k. This is to be considered

as max. value and by using it will render the

max. gain from the microphone. This level

of input signal that is unnecessary high will

result in clipping in the microphone amplifier

and could in mute condition permeate

through the input to the circuits reference

V

16

14

12

10

8

6

4

2

20

40

60

Figure 7. DC-characteristics. (R6 = 75Ω)

(a)

PBL 385 70

11

12

M

13 +

Dynamic

microphone

R

C+

(c)

11

4

PBL 385 70

12

M

13 +

Balanced electret microphone.

An additional RC filterlink is

recommended if pin 4 is used

as a supply.

Figure 8. Microphone options.

6

V telephone line

V line

V pin 4

V pin 2

V pin 8 o. 9

(DC supply)

IL

80

100

120

mA

(b)

4 PBL 385 70

11

12

M

13 +

Unbalanced electret

mic. with balanced

signal, DC-supply from

pin 4.

DC

Pin 8 or 9.

(d)

11

12

PBL 385 70

M

13 +

Balanced electret

microphone

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