ERICSSON PBL 385 41 User Manual

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PBL 385 41

November 1998

PBL 385 41

Universal Speech Circuit

Description.

PBL 38541 is a monolithic integrated speech transmission circuit for use in electronic telephones or in any other line interface application. High settable supply current for auxiliary functions, up to 6.0 mA (at high line currents). The circuit is designed to accomodate either a low impedance dynamic or an electret microphone. Microphone can be muted separately. Payphone signaling and DTMF dialling tones have a separate input that is controlled by a mute signal. A signal summing point is available at the transmitter input. An internally preset line length compensation can be adjusted with external resistors to fit into different current feed systems as for ex. 48 V, 2 x 200 ohms, 48 V, 2 x 400 ohms and 48 V, 2 x 800 ohms. The line length compensation can be shut off in either high or low gain mode. Application dependent parameters such as line balance, side tone level, transmitter and receiver gains and frequency responces are set independently by external components which means an easy adaption to various market needs. The setting of the parameters if carried out in certain order will counteract the interaction between the settings. The circuit provides four different DC - supplies to feed microphones,diallers and other more current consuming functions like handsfree systems.

Pin numbers in this datasheet refer to 18-pin DIP package unless otherwhise noted.

2311

PBL 385 41

Telephone line

DTMF

input

Mic.

Mute

(active low)

- output for

DC1 external devices

DC2 - output for external devices

DC-supply

Gain regulation

Key features.

• Minimum number of external components, with two filtered DCsupplies, 7 capacitors and 11 resistors.

• Easy adaption to various market needs.

• Mute control input for operation with DTMF - generator.

• A separate signaling input for payphone and DTMF tones controlled by mute.

• Transmitter and receiver gain regulation for automatic loop loss compensation.

• Extended current and voltage range 4 - 130 mA, down to 2 .2V.

• Differential microphone input for good balance to ground.

• Balanced receiver output stage.

• One stabilized DC - supply for low current CMOS diallers and or electret microphones. One settable current limited supply with 6 mA max. current.

• Short start up time.

• Excellent RFI performance.

• 18 - pin DIP and 20 - pin SO packages.

PBL 385 41

1. Impedance to the line and radio interference suppression

2. Transmitter gain and frequency responce network

3. Receiver gain and frequency responce network

4. Sidetone balance network

5. DC supply components

Figure 1. Functional diagram DIP package.

20-pin plastic SO

PBL 385 41

18-pin plastic DIP

PBL 385 41

= 350Ω

+ LINE

- LINE

ARTIFICIAL

LINE

R = 0-4kΩ

0 ohm when artificial line is used

MUTE

PBL 385 41 with external components

See fig. 4

Mic

= 350Ω

Rec

MIC

REC

feed

= 400Ω+400Ω

600Ω

E = 48.5V

DC1

C = 1µF when artificial line is used 470µF when no artificial line

DC2

DC1

DC2

5H+5H

+ LINE

- LINE

R = 0 - 4kΩ

MUTE

PBL 385 41

with external

components

See fig. 4

Mic

Rec

MIC

REC

feed

= 400Ω+400Ω

600Ω

E = 50.0V

1µF

Uz= 15-16V

5H+5H

DC1

DC2

DC1

DC2

= 350Ω

Maximum Ratings

Parameter Symbol Min Max Unit

Line voltage, tp = 2 s V Line current, continuous DIP I Line current, continuous SO package I Operating temperature range T Storage temperature range T

No input should be set on higher level than pin 4 (+C).

L L L

Amb

Stg

018V 0 130 mA 0 100 mA

-40 +70 °C

-55 +125 °C

Figure 2. Test set up without rectifier bridge.

220n DTMF input

R16

Mic.

2.7k

350Ω

Mute

(active low)

DC1 - output for external devices

DC2 - output for external devices

47µF

Figure 3. Test set up with rectifier bridge.

+Line

100n

75Ω

>0.5W

PBL 385 41

2311

910Ω

560Ω

100n

R14

R10

47n

6.2k

R12

R13

11k

10Ω

R9 11k

R2b

R11

62k

310Ω

Rec. 350Ω

910Ω

C2 15n

47µF

-Line

Figure 4. Circuit with external compon-

Ω

ents for test set up. 2 x 400

48V. * Not used in test set up. DIP package pinning.

DC-supply

Gain

R17

regulation

C11

47µF

R4 18k

R5 22k

R2a

PBL 385 41

Electrical Characterisics

At T

= + 25° C. No cable and line rectifier unless otherwise specified.

Amb

Ref.

Parameter fig. Conditions Min Typ Max Unit

Line voltage, V

2I 2I

Transmitting gain, note 1 20 •

2R 2R 2R

= 15 mA 3.3 3.7 4.1 V

= 100 mA 11 13 15 V

log (V2 / V3); 1 kHz

= 0 41 43 45 dB

= 400 Ω 43.5 45.5 47.5 dB

= 900 Ω - 2.2 kΩ 46 48 50 dB

Transmitting range of 2 1 kHz, RL = 0 to 900 Ω 3 5 7 dB regulation Transmitting frequency 2 200 Hz to 3.4 kHz -1 1 dB response Transmitter input impedance, pin 3 2 1 kHz 13.5 17 20.5 kΩ Microphone input impedance 2 1.7//(2.7) note 3 kΩ

Transmitter dynamic output 2 200 Hz - 3.4 kHz 1.5 V

≤ 2% distortion, IL = 20 - 100 mA Transmitter max output 2 200 Hz - 3.4 kHz 3 V

IL = 0 - 100 mA, V3 = 0 - 1 V Transmitter output noise 2 Psoph-weighting, Rel 1 V

, RL = 0 -75 dB

rms

Psoph

Receiving gain, note 1 20 • 10 log (V4 / V1); 1 kHz 2 R 2 R

= 0 Ω -18.5 -16.5 -14.5 dB

= 400 Ω -16 -14 -12 dB

2 RL = 900 Ω - 2.2 kΩ -13.5 -11.5 -9.5 dB Receiving range of regulation 2 1 kHz, RL = 0 to 900 Ω 3 5 7 dB Receiving frequency response 2 200 Hz to 3.4 kHz -1 1 dB Receiver input impedance 2 1 kHz, 38 kΩ Receiver output impedance 2 1 kHz, 3(+310)note 3 Ω Receiver dynamic output 2 200 Hz - 3.4 kHz 0.5 V

note 2 ≤ 2% distortion, IL = 20 - 100 mA Receiver max output 3 Measured with line rectifier 0.9 V

200 Hz - 3.4 kHz, IL = 0 - 100 mA,

V1= 0 - 50 V

Receiver output noise 2 A-weighting, Rel 1V

0 - 3 km, Ø = 0.4 mm

, with cable -85 dB

rms

0 - 5 km, Ø = 0.5 mm, Mute input voltage 2 0.3 V at mute (active low) DC

-supply voltage 2 IL = 20 - 100 mA

Pin 9 R17 = 4k; I

=2 mA 3.4 3.7 4.0 V

DC1

DC2-supply voltage 2 IL = 20 - 100 mA Pin 8 I

= 0 mA 2.1 2.35 2.6 V

IDC = 2 mA 1.95 2.2 2.6 V DC-output pin 8 input 4 VDC = 2.35 V 0.1 µA leakage current (no supply) DTMF transmitting gain 2 VM = 0.3 V, 1 kHz 24.5 26.5 28.5 dB DTMF input impedance 2 1 kHz 20 25 30 kΩ

Notes

1. Adjustable to both higher and lower values with external components.

2. The dynamic output can be doubled, see applications information.

3. External resistor in the test set up.

4. The DC output voltage is reduced at low line voltage (see page 8).

PBL 385 41

1 2 3 4 5 6 7 8

19 18 17 16 15 14 13

Mute

DCS

DCO

RE 2 RE 1 DR RI

-L MI 2 MI 1 MO

DCO

DI NC

4 5

17 16

Mute

DCS

DCO

9 10

RE 2

RE 1

-L

MI 2

MI 1

18-pin DIP

20-pin SO

Figure 5. Pin configuration.

Pin Descriptions

Refer to figure 5.

DIP SO Name Function

1 1 +L Output of the DC-regulator and transmitter amplifier, connected to the line through a polarity

guard diode bridge.

2 2 TO Output of the transmitter amplifier, connected through a resistor of 47 to 100 ohm to -L,

sets the DC-resistance of the circuit. The output has a low AC output impedance and the

signal is used to drive a side tone balancing network. 3 3 TI Input of the transmitter amplifier. Input impedance 17 kohm ± 20 %. 4 4 +C Positive power supply terminal for most of the circuitry inside the PBL 385 41 (about 1 mA current

consumption). The +C pin must be connected to a decoupling capacitor of 47 µF to 150 µF. 5 5 Mute When low, speech circuit is muted and the DTMF input is enabled. Maximum voltage (at mute) is

0.3 V, current sink requirement of external driver is 50 µA. 6 6 GR Control input for the gain regulation function. 7 7 DCS 1 Control input to the DC1-supply. A resistor to -line sets the maximum current load of the supply. 8 8 DCO 2 Output of the DC2-supply. 9 9 DCO 1 Output of the DC1-supply. 10 12 DI Input for the DTMF-signal. Input impedance 25 kohm ± 20 %. 11 13 MO Output of the microphone amplifier or DTMF-amplifier. 12 14 MI 1 13 15 MI 2

}

14 16 -L The negative power terminal, connected to the line through a polarity guard diode bridge. 15 17 RI Input of receiver amplifier. Input impedance 38 kohm ± 20 %. 16 18 DR Control input for the receiver amplifier driving capability. 17 19 RE 1 18 20 RE 2

10 Not connected 11 Not connected

Inputs to the microphone amplifier. Input impedance 1.7 kohm ± 20 %.

Receiver amplifier outputs. Output impedance is approximately 3 ohm.

}

PBL 385 41

Functional description

Design procedure; ref. to fig.4. The design is made easier through that all

settable parameters are returned to ground (-line), this feature differs it from bridge type solutions.To set the parameters in the following order will result in that the interaction between the same is minimized.

1. Set the circuit impedance to the line, either resistive (600Ω) or complex. (R3 and C1). C1 should be big enough to give low impedance compared with R3 in the telephone speech frequency band.Too large C1 will make the start-up slow. See fig. 6.

2. Set the DC-characteristic that is required in the PTT specification or in case of a system telephone,in the PBX specification(R6). Observe the power dissipated.There are also internal circuit dependent requirements like supply voltages etc.

3. Set the attac point where the line length regulation is supposed to cut in (R1 and R2). Note that in some countries the line length regulation is not allowed. In most cases the end result isbetter and more readily achieved by using the line length regulation (line loss compensation) than without. See fig. 13.

4. Set the transmitter gain and frequency response.

5. Set the receiver gain and frequency response. See text how to limit the max. swing to the earphone.

6. Adjust the side tone balancing network.

7. Set the RFI suppression components in case necessary. In two piece telephones the often ”helically” wound cord acts as an aerial. The microphone input with its high gain is especially sensitive.

8. Circuit protection. Apart from any other protection devices used in the design a good practice is to connect a 15V 1W zener diode across the circuit , from pin 1 to -Line.

Figure 7. Block connections.

AM AT

Transmitter summing input

Mute

PBL 385 41

Figure 6. AC-impedance.

Impedance to the line

The AC- impedance to the line is set by R3, C1 and C2. Fig.6. The circuits relatively high parallel impedance will not influence it to any noticeable extent. At low frequencies the influence of C1 can not be neglected. Series resistance of C1 that is dependent on the temperature and the quality of the component will cause some of the line signal to enter pin 4. This generates a closed loop in the transmitter amplifier that in it´s turn will create an active impedance thus lowering the impedance to the line. The impedance at high frequencies is set by C2 that also acts as a RFI suppressor.

In many specifications the impedance towards the line is specified as a complex network. See fig. 6. In case a). the error signal entering pin 4 is set by the ratio ≈Rs/R3 (910Ω), where in case b). the ratio at high frequencies will be Rs/220Ω because the 820Ω resistor is bypassed by a capacitor. To help up this situation the

+ Line

- Line

+Line

a) b) c)

220Ω

820Ω

Example:

How to connect a

≈1Ω

complex network. 220Ω+820Ω//Cx

-Line

complex network capacitor is connected directly to ground, case c). making the ratio Rs/220Ω+820Ω and thus lessening the error signal. Conclusion: Connect like in case c) when complex impedance is specified.

DC - characteristic

The DC - characteristic that a telephone set has to fulfill is mainly given by the network administrator. Following parameters 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 2 x.......

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. 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 transmitter output amplifier, receiver output amplifier, dialler, speech switching and loudspeaker amplifier in a handsfree telephone etc.

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