Philips TEA1085T, TEA1085AT, TEA1085A, TEA1085 Datasheet

INTEGRATED CIRCUITS

DATA SH EET

TEA1085; TEA1085A

Listening-in circuit for line-powered telephone sets

Preliminary speciﬁcation File under Integrated Circuits, IC03A

March 1992

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

FEATURES

• Internal supply optimum current split-up

- low constant current (adjustable) in transmission IC

- nearly all line current available for listening-in adjustable supply voltage

• Loudspeaker amplifier dynamic limiter providing low distortion and the

highest possible output power SE or BTL drive for loudspeaker volume control by potentiometer and/or logic inputs (e.g. microcontroller drive) fixed gain of 35 dB

• Larsen level limiter low sensitivity for own speech due to 3rd-order filter

and attack delay adjustable voltage thresholds

• Power down input

• MUTE input

TEA1085/TEA1085A

- clickfree switching between listening-in mode and standby mode

TEA1085

- toggle function

- start-up in standby condition TEA1085A

- logic level input

TEA1085; TEA1085A

GENERAL DESCRIPTION

The TEA1085 and TEA1085A are bipolar ICs which have been designed for use in line-powered telephone sets and provide a listening-in facility for the received line signal via a loudspeaker. Nearly all the line current can be used for powering the loudspeaker. The circuits incorporate a supply circuit, loudspeaker amplifier dynamic limiter, MUTE circuit, power-down facility and logic inputs for gain setting. The devices also incorporate a Larsen Level Limiter to reduce howling effects. The ICs are intended for use in conjunction with a transmission circuit of the TEA1060 family.

ORDERING INFORMATION

EXTENDED TYPE

NUMBER

TEA1085/TEA1085A 24 DIL plastic SOT101B TEA1085T/TEA1085AT 24 SO24 plastic SOT137A

Notes

1. SOT101-1; 1998 Jun 18.

2. SOT137-1; 1998 Jun 18.

March 1992 2

PINS PIN POSITION MATERIAL CODE

PACKAGE

(1) (2)

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered

TEA1085; TEA1085A

telephone sets

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

SUP

∆G

SUP

ad(RMS)

DTI(RMS)

amb

input current range 4 − 120 mA stabilized supply voltage − 3.6 − V current consumption PD = HIGH − 55 −µA voltage gain loudspeaker ampliﬁer

SE − 35 − dB BTL − 41 − dB

maximum gain reduction with logic

− 18 − dB

inputs (3 steps) minimum input current

= 20 mW typ.

OUT

− 15 17 mA

into 50 Ω SE P

= 40 mW typ.

OUT

−−32 mA

into 50 Ω BTL

Larsen limiter attack delay time V

DTI

100 − 200 ms

jumps from 0 to ≥ 100 mV (RMS value) Larsen limiter threshold level Larsen mode − 7 − mV Larsen limiter preampliﬁer gain setting

30 − 52 dB

range operating ambient temperature range −25 −+75 °C

March 1992 3

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March 1992 4

dbook, full pagewidth

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered

telephone sets

line

TEA1060

(LN)

(1)

SREF 4

SUPPLY

SUP3SDC 2

(1)

THL1 14

THL212LLC 13

LARSEN

LEVEL

LIMITER

DCA 16

DTI 15

(1)

QLA 11

PREAMPLIFIER LEVEL LIMITER

LARSEN

LAI−

109LAI+

TEA1060

(MIC)

TEA1060

(MIC)

TEA1085

GSC1 8 GSC2 7

(1)

SIC 17

I-STABILIZATION

LOGIC GAIN

CONTROL

PEAK AND CURRENT

LIMITER

2 2 2

RECEIVING

AMPLIFIER

MUTE

TEA1085A

POWER

AMPLIFIER

START

CIRCUIT

QLS1

2221QLS2

TEA1085; TEA1085A

(1) To TEA1060 (SLPE). (2) See Fig.16.

23 DLC

(1)

20 5 MUTE LSI1 LSI2

(2)

MGR032

TEA1060 (VEE) TEA1060 (QR)

(1)

Fig.1 Block diagram.

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

PIN CONFIGURATION

SYMBOL PIN DESCRIPTION

SUP 2 positive supply SDC 3 supply ampliﬁer decoupling SREF 4 supply reference input LSI1 5 loudspeaker ampliﬁer input 1 LSI2 6 loudspeaker ampliﬁer input 2 GSC2 7 logic input 2 for gain select GSC1 8 logic input 1 for gain select LAI− 9 Larsen limiter preampliﬁer inverting

LAI+ 10 Larsen limiter preampliﬁer

QLA 11 Larsen limiter preampliﬁer output LLC 12 Larsen limiter capacitor THL2 13 Larsen limiter residual threshold level THL1 14 Larsen limiter attack delay threshold

DTI 15 Larsen limiter detector input DCA 16 Larsen limiter detector current

SIC 17 Larsen limiter current stabilizer VA 18 V PD 19 power-down input MUTE 20 MUTE input QLS1 21 loudspeaker ampliﬁer output 1 QLS2 22 loudspeaker ampliﬁer output 2 DLC 23 dynamic limiter capacitor V

1 negative supply

input

non-inverting input

level

adjustment

voltage adjustment

24 stabilized supply decoupling

handbook, halfpage

TEA1085; TEA1085A

SUP

SDC

SREF

LSI1

LSI2

TEA1085

GSC2 GSC1

LAI− LAI+

QLA

LLC

TEA1085A

7 8

9 10 11 12

MLA415

Fig.2 Pin configuration.

DLC

QLS2

QLS1

MUTE

20 19

PD VA

18 17

SIC DCA

DTI

THL1

THL2

March 1992 5

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

FUNCTIONAL DESCRIPTION

Figure 1 illustrates a block diagram of the TEA1085/TEA1085A with external components and connections to the transmission IC. The TEA1085/TEA1085A are bipolar ICs which have been designed for use in line-powered telephone sets and provide a listening-in facility for the received line signal via a loudspeaker. Nearly all the line current can be used for powering the loudspeaker. The loudspeaker amplifier consists of a preamplifier, to amplify the earpiece signal from the transmission circuit and, a double push-pull output stage to drive the loudspeaker in the BTL (bridge tied load) or SE (single ended) configuration. The gain of the preamplifier is controlled by a dynamic limiter which prevents high distortion of the loudspeaker signal. This is achieved by preventing clipping of the loudspeaker signal, with respect to the supply voltage, and at too low supply current. Two logic inputs can be used to reduce the gain in 3 steps. Because of acoustic feedback from the loudspeaker to the microphone, howling signals (Larsen effect) can occur on the telephone line and in the loudspeaker. When the Larsen signal exceeds a voltage and time duration threshold the Larsen level limiter (LLL) will reduce the

TEA1085; TEA1085A

Larsen signal to a low level within a short period of time by reducing the gain of the receiving preamplifier. This is achieved by using the microphone signal as an input signal which is processed in the LLL via a preamplifier and 3rd-order filter. The MUTE input can be used to enable or disable the loudspeaker amplifier. The MUTE function of the TEA1085 has a toggle input to permit the use of a simple push-button switch. The MUTE function of the TEA1085A has a logic input to operate with a microcontroller. By activating the power-down input the current consumption of the circuit will be reduced, this enables pulse dialling or flash (register recall). An internal start circuit ensures normal start-up of the transmission IC and start-up of the listening-in IC in the standby mode. The TEA1085/TEA1085A are intended for use in conjunction with a member of the TEA1060 family and should be connected between LINE and SLPE of the transmission IC. The transmission characteristics (impedance, gain settings, for example) are not affected. The interconnection between the two ICs is illustrated in Fig.3.

handbook, full pagewidth

LINE

TEA1060

EE SLPE

MIC+

MIC−

Fig.3 Interconnection of the TEA1085/TEA1085A with the TEA1060.

March 1992 6

SREF SUP

LAI+

TEA1085

TEA1085A

LAI−

LSI1 LSI2

MGR033

QLS

to TEA1060

(SLPE)

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

Supply; SUP, SREF, VBB, VSSand VA

The line current is divided into I The supply arrangement is illustrated in Fig.4.

handbook, full pagewidth

LINE

line

for the TEA1060 and I

TEA1060

EE SLPE

R20

SUP

SREF

TEA1085

TEA1085A

for the TEA1085/TEA1085A.

SUP

TR1

int

TR2

BIAS

TEA1085; TEA1085A

BBO

VOLTAGE

STABILIZER

R38

C20

ITR is constant: ITR=V

/ R20; I

int

SUP=Iline

− ICC− I

Fig.4 Supply arrangement.

Where:

int

is an internal temperature compensated reference voltage with a typical value of

315 mV between SUP and SREF R20 is a resistor between SUP and SREF I

is the internal current consumption of the

TEA106X (≈ 1 mA)

A practical value for R20 is 150 Ω. This value of resistance produces a value for I

= 2 mA and I

SUP

= I

line

− 3 mA.

The TEA1085/TEA1085A stabilizes its own supply voltage at VBB. Transistor TR1 provides the supplies for the internal circuits. TR2 is used to minimize the signal distortion on the line by momentarily diverting the input current to VSS whenever the instantaneous value of the voltage V

drops below the supply voltage VBB. VBB is

SUP

fixed to a typical value of 3.6 V but can be increased by means of an external resistor (R38) connected between

MGR034

VA and VSS or decreased by connecting this resistor between VA and VBB. The minimum level on VBB is restricted to 3.0 V; the level of the VBB limiter is also affected (see application report for further information). The supply at VBB is decoupled by a 470 µF capacitor.

The DC voltage (V transmission IC (V V

− VSS = V

SUP

LN−SLPE

− VSS) is determined by the

SUP

+ V

); thus:

int

LN−SLPE

The minimum DC voltage that can be applied to this input is V

Where: V

BB(max)

+ 0.4 V.

is the worst case supply voltage (this

BB(max)

depends on the setting of R38, which is connected between VA and VSS).

The internal current consumption of the TEA1085/TEA1085A (I V

− VSS = 4.5 V, MUTE off). Thus the current available

SUP

for powering the loudspeaker is I The current I

consists of a bias current of ≈ 0.4 mA for

SUP0

the circuitry connected to SUP and current I

) is typically 4.2 mA (where

SUP0

− I

SUP0

BB0

SUP

of≈ 3.8 mA

which is used for the circuitry connected to VBB(see Fig.4).

March 1992 7

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

5.5

dbook, halfpage

(V)

5.1

4.7

4.3

3.9

3.5 10 10

R38 (kΩ)

MGR035

VBB = 3.60 V

TEA1085; TEA1085A

Logic gain control (GSC1 and GSC2) pins 7 and 8

The logic inputs GSC1 and GSC2 can be used to reduce the gain of the loudspeaker amplifier by means of the logic gain control function in 3 steps of 6 dB.

Table 1 Data for microcontroller drive of logic inputs

GSC2 GSC1

gain

(dB)

0 0 35 0 0 1 28.7 6.3 1 0 22.2 12.2 1 1 17 18

Where:

0 = connection to VSS or left open-circuit 1 = applying a voltage ≥ VSS+ 1.5 V

gain reduction

(dB)

Fig.5 Stabilized supply voltage as a function of

R38.

Supply ampliﬁer stability (SDC) pin 3

To ensure stability of the TEA1085/TEA1085A, in combination with a transmission IC of the TEA1060 family, a 47 pF capacitor connected between SDC and SUP and a 150 µH coil connected between SUP and the positive line terminal (Fig.16) is required.

Loudspeaker ampliﬁer (LSI1/LSI2 and QLS1/QLS2) pins 5/6, 21/22

The TEA1085/TEA1085A have symmetrical inputs at LSI1 and LSI2. The input signal is normally taken from the earpiece output of the transmission circuit via a resistive attenuator (see Fig.3). The amount of attenuation must be chosen in accordance with the receive gain of the transmission IC (which depends on the sensitivity of the earpiece transducer). The maximum input signal level is 450 mV(RMS) at T

= +25 °C.

amb

The outputs QLS1 and QLS2 can be used for single ended drive (SE) or bridge tied load drive (BTL). The output stages have been optimized for use with a 50 Ω loudspeaker (e.g. Philips type AD2071). The gain of the amplifier is fixed to ≈ 35 dB for the SE drive and ≈ 41 dB for the BTL drive (when the inputs for logic control are left open-circuit or are connected to VSS). The volume control can be obtained by using a potentiometer at the input and/or by the logic control function.

March 1992 8

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

Dynamic limiter (DLC) pin 23

To prevent distortion of the signal at the loudspeaker outputs the gain of the amplifier is reduced rapidly when:

• the peaks of the signal at the loudspeaker outputs exceed an internally determined threshold (voltage limiter)

• the DC current into SUP is insufficient (current limiter)

• the voltage at VBB decreases below an internally

determined threshold, typically 2.9 V (VBB limiter)

The time in which the gain reduction is effected is the 'attack time'; this is very short in the first and third instance and relatively long in the second instance. The circuit will remain in the gain-reduced condition until the peaks of the output signal remain below the threshold level. The gain will then return to a nominal level after a time determined by the capacitor connected to DLC (release time).

TEA1085; TEA1085A

MUTE input (MUTE) pin 20; TEA1085A

This MUTE is provided with a logic input to operate with a microcontroller for instance. The loudspeaker amplifier is disabled when the MUTE input is LOW (connected to VSS or open input). A HIGH level at the MUTE input enables the amplifier in the listening-in mode.

MUTE input (MUTE) pin 20; TEA1085

The MUTE function is provided with a toggle input and is designed to switch between the standby condition and the listening-in condition on the rising edge of the input MUTE signal (see Fig.6). In the basic application the MUTE input must be LOW (connected to V operate the MUTE toggle (see Fig.7). Debouncing can be realized by means of a small capacitor connected between MUTE and VSS. An internal start circuit ensures that the circuit always starts up in the standby condition.

). A simple push-button can be used to

handbook, full pagewidth

LSI1

MUTE

QLS1

standby standbylistening-in

Fig.6 Mute toggle function of the TEA1085.

MUTE MUTE

(a) Break contact. (b) Make contact.

10 kΩ

MGR036

MLA055

Fig.7 Mute switch alternatives with the TEA1085.

March 1992 9

Philips Semiconductors Preliminary speciﬁcation

Listening-in circuit for line-powered telephone sets

Power down input (PD) pin 19

During pulse dialling or register recall (timed loop break) the telephone line is interrupted, thereby breaking the supply to the transmission and listening-in circuits. The capacitor connected to VBB provides the supply for the listening-in circuit during the supply breaks. By making the PD input HIGH during the loop break the requirement on the capacitor is eased and, consequently, the internal (standby) current consumption I VBB is reduced from 3.8 mA to 400 µA typical. So that the transmission circuit is not affected transistors TR1 and TR2 are inhibited and the bias current is reduced from ≈ 0.4 mA to ≈ 55 µA with V

= 4.5 V in the following

SUP

equation: I (where 4.2 V < V

SUP(PD)

= I

BIAS(PD)

= (V

< VBB+ 3 V)

SUP

− 2Vd) / Ra

SUP

2Vd = the voltage drop across 2 internal diodes (≈ 1.3 V) Ra = an internal resistor of typical 60 kΩ

(Fig.4) at

BBO

TEA1085; TEA1085A

= 1.25 / R36; when R36 = 120 kΩ, I

SIC

Changing the value of R36 will affect the timing of the Larsen level limiter system.

Larsen limiter preampliﬁer (LAI1/LAI2 and QLA) pins 9/10 and 11

This circuit amplifies the microphone signal to a level suitable for the Larsen limiter detector. The gain is set by external components (see Fig.8). Normally the gain is set to the same level as the microphone amplifier of the transmission circuit, this ensures that the output signal level at output QLA is equal to the line signal level.

The gain between QLA and the microphone input is given by the following equation (the high-pass filter is not taken into account):

pre

= V

/ VM = R29 / R26; in the basic application

QLA

R25 = R26 = 10 kΩ

= 10.5 µA

SIC

Larsen limiter current stabilizer (SIC) pin 17

A current reference is set by resistor R36 between SIC and V

. The preferred value is 120 kΩ. The internal reference

current is given by the following equation:

QLA

handbook, full pagewidth

R29

C23

R26

R25

C22

LAI−

LAI+

R28

R27

−

The gain can be adjusted between 30 dB (R29 = 316 kΩ) and 52 dB (R29 = 4 MΩ). The impedance result of R28 and R27 in parallel must be equal to R29 (e.g. R27 = R28 = 2 × R29).

R32C25

R30

DTI

−

LLC

C24

R31

DCA

LARSEN

DETECTOR

THL1 THL2

R33

DCA

Fig.8 Larsen limiter preamplifier and voltage/current converter.

March 1992 10

R35 R34

MGR037

+ 22 hidden pages