Philips TEA1099H-C1 Datasheet

DATA SH EET

Product speciﬁcation Supersedes data of 1998 Jun 11 File under Integrated Circuits, IC03

1999 Apr 08

INTEGRATED CIRCUITS

TEA1099H

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

1999 Apr 08 2

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

FEATURES Line interface

• Low DC line voltage

• Voltage regulator with adjustable DC voltage

• Symmetrical high impedance inputs (70 kΩ) for

dynamic, magnetic or electret microphones

• Dual Tone Multi-Frequency (DTMF) input with confidence tone on earphone and/or loudspeaker

• Receive amplifier for dynamic, magnetic or piezo-electric earpieces (with externally adjustable gain)

• AGC: Automatic Gain Control for true line loss compensation.

Supplies

• Provides a strong 3.35 V regulated supply for microcontroller or dialler

• Provides filtered power supply, optimized according to line current and compatible with external voltage or current sources

• Filtered 2.0 V power supply output for electret microphone

• Compatible with a ringer mode

• Power-Down (

PD) logic input for power-down.

Handsfree

• Asymmetrical high-impedance input for electret microphone

• Loudspeaker amplifier with single-ended rail-to-rail output and externally adjustable gain

• Dynamic limiter on loudspeaker amplifier to prevent distortion

• Logarithmic volume control on loudspeaker amplifier via linear potentiometer

• Duplex controller consisting of: – Signal and noise envelope monitors for both

channels (with adjustable sensitivities and timing)

– Decision logic (with adjustable switch-over and Idle

mode timing)

– Voice switch control (with adjustable switching range

and constant sum of gain during switching).

Auxiliary interfaces

• General auxiliary output for transmit and receive purposes

• Auxiliary transmit input with high signal level capability dedicated to line transmission

• Auxiliary receive input with high signal level capability

• Integrated multiplexer for channels selection.

APPLICATIONS

• Line powered telephone sets

• Cordless telephones

• Fax machines

• Answering machines.

GENERAL DESCRIPTION

The TEA1099H is an analog bipolar circuit dedicated for telephone applications. It includes a line interface, handset (HS) microphone and earpiece amplifiers, handsfree (HF) microphone and loudspeaker amplifiers, some specific auxiliary Inputs/Outputs (I/Os) and an analog multiplexer to enable the right transmit and/or receive channels. The multiplexer is controlled by a logic circuit which decodes four logic inputs provided by a microcontroller. Thirteen different application modes have been defined and can be accessed by selecting the right logic inputs. An application mode is a special combination of transmit and receive channels required by telephone applications.

This IC can be supplied by the line and/or by the mains if available (in a cordless telephone or an answering machine for example). It provides a 3.35 V supply for a microcontroller or dialler and a 2.0 V filtered voltage supply for an electret microphone. The IC is designed to facilitate the use of the loudspeaker amplifier during ringing phase.

1999 Apr 08 3

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

QUICK REFERENCE DATA

line

= 15 mA; R

SLPE

=20Ω; Z

line

= 600 Ω; f = 1 kHz; T

amb

=25°C; AGC pin connected to LN; PD = HIGH; HFC = LOW;

AUXC = LOW;

MUTT = HIGH; MUTR = HIGH; measured according to test circuits; unless otherwise speciﬁed.

ORDERING INFORMATION

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

line

line current operating range normal operation 11 − 140 mA

with reduced performance 1 − 11 mA

SLPE

stabilized voltage between SLPE and GND (V

ref

)

line

= 15 mA 3.4 3.7 4.0 V

line

= 70 mA 5.7 6.1 6.5 V

regulated supply voltage for internal circuitry

line

= 15 mA 2.75 3.0 3.25 V

line

= 70 mA 4.9 5.3 5.7 V

regulated supply voltage on pin V

VBB> 3.35 V + 0.25 V (typ) 3.1 3.35 3.6 V otherwise − V

− 0.25 − V

ESI

external voltage supply allowed on pin ESI

−− 6V

ESI(ext)

external current supply allowed on pin ESI

−− 140 mA

current available on pin V

speech mode − 11 − mA handsfree mode − 9 − mA

BB(pd)

current consumption on V

during power-down phase

PD = LOW − 460 −µA

v(MIC-LN)

voltage gain from pin MIC+/MIC− to LN

MIC

= 5 mV (RMS) 43.3 44.3 45.3 dB

v(IR-RECO)

voltage gain from pin IR (referenced to LN) to RECO

VIR= 15 mV (RMS) 28.7 29.7 30.7 dB

∆G

v(QR)

gain voltage range between pins RECO and QR

−3 − +15 dB

v(TXIN-TXOUT)

voltage gain from pin TXIN to TXOUT

TXIN

= 3 mV (RMS);

GATX

= 30.1 kΩ

12.7 15.2 17.7 dB

v(HFTX-LN)

voltage gain from pin HFTX to LN V

HFTX

= 15 mV (RMS) 33.5 34.7 35.9 dB

v(HFRX-LSAO)

voltage gain from pin HFRX to LSAO

HFRX

= 20 mV (RMS);

GALS

= 255 kΩ

25.5 28 30.5 dB

SWRA switching range − 40 − dB ∆SWRA switching range adjustment with R

SWR

referenced to

365 kΩ

−40 − +12 dB

∆G

v(trx)

gain control range for transmit and receive ampliﬁers affected by the AGC; with respect to I

line

=15mA

line

= 70 mA; on

v(MIC-LN)

, G

v(IR-RECO)

and

v(IR-AUXO)

5.45 6.45 7.45 dB

TYPE

NUMBER

PACKAGE

NAME DESCRIPTION VERSION

TEA1099H QFP44 plastic quad ﬂat package; 44 leads (lead length 1.3 mm);

body 10 × 10 × 1.75 mm

SOT307-2

1999 Apr 08 4

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

BLOCK DIAGRAM

Fig.1 Block diagram.

handbook, full pagewidth

MGM296

LINE CURRENT DETECTION LOW VOLTAGE BEHAVIOUR

TX AND RX

ENVELOPE AND NOISE

DETECTORS

SUPPLY

MANAGEMENT

SWITCH

STARTER

AGC

ATT.

GND

ESI V

MICS

AGC

REG SLPE 16 14

Tail currents for preamps

HFTX 36

TSEN 4 TENV 3

TNOI 2

RNOI 5 RENV 7 RSEN 6

LSAO 12

DLC 8

GALS 11

TXAUX 43

MIC+ 31 MIC−

DTMF 32

POWER-DOWN

CURRENT SOURCES

ANALOG

MULTIPLEXER

CONTROL

BUFFERS

AND

COMPARATORS

DYNAMIC

LIMITER

DUCO LOGIC SWT STATUS

VOICE

SWITCH

VOLUME

CONTROL

HFC37 MUTT39 MUTR40 AUXC41

GATX27

TXOUT26

SWT24 IDT25

STAB21

SWR22

VOL23

HFRX

IR17

RAUX42

GNDTX29

TXIN 28

AUXO 44

RECO 35

QR 33

GARX 34

TEA1099H

1999 Apr 08 5

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

PINNING

SYMBOL PIN DESCRIPTION

HFRX 1 receive input for loudspeaker

ampliﬁer or auxiliary receive ampliﬁer

TNOI 2 transmit noise envelope timing

adjustment

TENV 3 transmit signal envelope timing

adjustment

TSEN 4 transmit signal envelope sensitivity

adjustment

RNOI 5 receive noise envelope timing

adjustment

RSEN 6 receive signal envelope sensitivity

adjustment

RENV 7 receive signal envelope timing

adjustment

DLC 8 dynamic limiter capacitor for the

loudspeaker ampliﬁer ESI 9 external supply input V

10 stabilized supply for internal

circuitry GALS 11 loudspeaker ampliﬁer gain

adjustment LSAO 12 loudspeaker ampliﬁer output GND 13 ground reference SLPE 14 line current sense LN 15 positive line terminal REG 16 line voltage regulator decoupling IR 17 receive ampliﬁer input AGC 18 automatic gain control/line loss

compensation V

19 3.35 V regulated voltage supply for

the microcontroller

MICS 20 microphone supply output STAB 21 reference current adjustment SWR 22 switching range adjustment VOL 23 loudspeaker volume adjustment SWT 24 switch-over timing adjustment IDT 25 Idle mode timing adjustment TXOUT 26 HF microphone ampliﬁer output GATX 27 HF microphone ampliﬁer gain

adjustment TXIN 28 HF microphone ampliﬁer input GNDTX 29 ground reference for microphone

ampliﬁers MIC− 30 negative HS microphone ampliﬁer

input MIC+ 31 positive HS microphone ampliﬁer

input DTMF 32 dual tone multi-frequency input QR 33 earpiece ampliﬁer output GARX 34 earpiece ampliﬁer gain adjustment RECO 35 receive ampliﬁer output HFTX 36 transmit input for line ampliﬁer or

auxiliary receive ampliﬁer HFC 37 logic input PD 38 power-down input (active LOW) MUTT 39 logic input (active LOW) MUTR 40 logic input (active LOW) AUXC 41 logic input RAUX 42 auxiliary receive ampliﬁer input TXAUX 43 auxiliary transmit ampliﬁer input AUXO 44 auxiliary ampliﬁer output

SYMBOL PIN DESCRIPTION

1999 Apr 08 6

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

Fig.2 Pin configuration.

handbook, full pagewidth

1 2 3 4

5 6 7 8 9

10 11

33 32 31 30 29 28 27 26 25 24 23

TEA1099H

MGM297

QR DTMF MIC+ MIC−

TXIN GATX TXOUT IDT SWT VOL

HFRX

TNOI TENV TSEN

RNOI

RSEN

DLC

ESI

GALS

GNDTX

TXAUX

RAUX

AUXC

MUTR

MUTT

HFTX

RECO

GARX

AUXO

HFC

GND

SLPE

REG

AGC

MICS

STAB

SWR

LSAO

RENV

FUNCTIONAL DESCRIPTION

All data given in this chapter are typical values, except when otherwise specified.

Supplies

INE INTERFACE AND INTERNAL SUPPLY (PINS LN, SLPE,

REG

AND V

)

The supply for the TEA1099H and its peripherals is obtained from the line. The IC generates a stabilized reference voltage (V

ref

) between pins SLPE and GND. This reference voltage is equal to 3.7 V for line currents lower than 18 mA. It than increases linearly with the line current and reaches the value of 6.1 V for line currents higher than 45 mA. For line currents below 9 mA, the internal reference voltage generating V

ref

is automatically adjusted to a lower value. This is the so-called low voltage area and the TEA1099H has limited performances in this area (see Section “Low voltage behaviour”). This reference voltage is temperature compensated.

The voltage between pins SLPE and REG is used by the internal regulator to generate the stabilized reference voltage and is decoupled by means of a capacitor between pins LN and REG. This capacitor converted into an equivalent inductance realizes the set impedance conversion from its DC value (R

SLPE

) to its AC value (done

by an external impedance). The IC regulates the line voltage at pin LN and it can be

calculated as follows:

where: I

line

= line current Ix= current consumed on pin LN (approximately a few µA) I

SLPE

= current flowing through the R

SLPE

resistor

refRSLPE

I×+

SLPE

SLPEIline

Ix–=

1999 Apr 08 7

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

The preferred value for R

SLPE

is 20 Ω. Changing this value will affect more than the DC characteristics; it also influences the transmit gains to the line, the gain control characteristic, the sidetone level and the maximum output swing on the line.

As can be seen from Fig.3, the internal circuitry is supplied by pin VBB, which is a strong supply point combined with the line interface. The line current is flowing through the R

SLPE

resistor and is sunk by the VBB voltage stabilizer, becoming available for a loudspeaker amplifier or any peripheral IC. Its voltage is equal to 3.0 V for line currents lower than 18 mA. It than increases linearly with the line current and reaches the value of 5.3 V for line currents greater than 45 mA. It is temperature compensated. See Fig.4 for the main DC voltages.

The aim of the current switch TR1 and TR2 is to reduce distortion of large AC line signals. Current I

SLPE

is supplied to VBB via TR1 when the voltage on SLPE is greater than VBB+ 0.25 V. When the voltage on SLPE is lower than this value, the current I

SLPE

is shunted to GND via TR2.

The reference voltage V

ref

can be increased by connecting an external resistor between pins REG and SLPE. For large line currents, this increase can slightly affect some dynamic performances such as maximum signal level on the line for 2% Total Harmonic Distortion (THD). The voltage on pin VBB is not affected by this external resistor.

Fig.3 Line interface principle.

handbook, full pagewidth

MGM298

TN2

TR2

TR1

TN1

TP1

GND

from

preamp

GND

REG

SLPE

REG

4.7 µF

SLPE

20 Ω

1999 Apr 08 8

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

Fig.4 Main DC voltages.

handbook, full pagewidth

0.070.06

0 0.01

voltages

(V)

0.02 0.05

MICS

SLPE

line

(A)

0.040.03

FCA049

EXTERNAL SUPPLY (PINS ESI AND VBB) The TEA1099H can be supplied by the line as well as by

external power sources (voltage or current sources) that must be connected to pin ESI.

The IC will choose which supply to use according to the voltage it can provide. A voltage supply on ESI is efficient only if its value is greater than the working voltage of the internal V

voltage stabilizer. Otherwise the IC continues to be line powered. The current consumed on this source is at least equal to the internal consumption. It increases with the voltage difference between the value forced on ESI and the working voltage of the internal stabilizer. The excess current compared to the internal consumption becomes then available for other purposes such as supplying a loudspeaker amplifier. The voltage source should not exceed 6 V. If the value of the external voltage source can be lower than the working voltage of the internal stabilizer, an external diode is required to avoid reverse current flowing into the external power supply.

In case of current source, the voltage on VBB and ESI depends on the current available. It is internally limited to

6.6 V. The current source should not exceed 140 mA.

SUPPLY FOR MICROCONTROLLER (PIN V

)

The voltage on V

supply point follows the voltage on V

with a difference typically equal to 250 mV and is internally limited to 3.35 V. This voltage is temperature compensated. This supply point can provide a current up to 3 mA typically. Its internal consumption stays low (a few 10 nA) as long as VDD does not exceed 1.5 V (see Fig.5).

An external voltage can be connected on VDD with limited extra consumption on VDD (typically 100 µA). This voltage source should not be lower than 3.5 V or higher than 6 V.

VBB and VDD can supply external circuits in the limit of currents provided either from the line or from ESI, taking into account the internal current consumption.

1999 Apr 08 9

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

Fig.5 Current consumption on VDD.

handbook, full pagewidth

1.0

(pA)

1.5 2.5 3.0 VDD (V)

2.0

FCA050

SUPPLY FOR MICROPHONE (PINS MICS AND GNDTX) The MICS output can be used as a supply for electret

microphones. Its voltage is equal to 2.0 V; it can source current up to 1 mA and has an output impedance equal to 200 Ω.

OW VOLTAGE BEHAVIOUR

For line currents below 9 mA, the reference voltage is automatically adjusted to a lower value; the VBB voltage follows the SLPE voltage with 250 mV difference. The excess current available for other purposes than DC biasing of the IC becomes small. In this low voltage area, the IC has limited performances.

When the VBB voltage reaches 2.7 V, the VBB detector of the receive dynamic limiter on LSAO acts and discharges the DLC capacitor. The loudspeaker is then automatically disabled below this DC voltage.

When VBB becomes lower than 2.5 V, the TEA1099H is forced into a low voltage mode whatever the levels on the logic inputs are. It is a speech mode with reduced performances only enabling the microphone channel (between the MIC inputs and LN) and the earpiece amplifier.

These two channels are able to deliver signals for line currents as small as 3 mA. The HFC input is tied to GND sinking a current typically equal to 300 µA.

OWER-DOWN MODE (PINS PD AND AUXC)

To reduce current consumption during dialling or register recall (flash), the TEA1099H is provided with a power-down input (PD). When the voltage on both pinsPD and AUXC is LOW, the current consumption from VBB and VDD is reduced to 460 µA typically. Therefore a capacitor of 470 µF on VBB is sufficient to power the TEA1099H during pulse dialling or flash. The

PD input has a pull-up structure, while AUXC has a pull-down structure. In this mode, the capacitor C

REG

is internally disconnected.

INGER MODE (PINS ESI, V

, AUXC AND PD)

The TEA1099H is designed to be activated during the ringing phase. The loudspeaker amplifier can be used for the ringing signal. The IC must be powered by an external supply on ESI, while applying a HIGH level on the logic input AUXC and a LOW level on

PD input. Only the HFRX input and the LSAO output are activated, in order to limit the current consumption. Some dynamic limitation is provided to prevent the LSAO output from saturation and VBB from being discharged below 2.7 V.

1999 Apr 08 10

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

Transmit channels (pins MIC+, MIC−, DTMF, TXAUX, HFTX and LN)

ANDSET MICROPHONE AMPLIFIER (PINS MIC+, MIC− AND

LN) The TEA1099H has symmetrical microphone inputs.

The input impedance between MIC+ and MIC− is 70 kΩ(typ.). The voltage gain between pins MIC+/MIC− and LN is set to 44.3 dB. Without limitation from the output, the microphone input stage can accommodate signals up to 18 mV (RMS) at room temperature for 2% of THD. The microphone inputs are biased at one diode voltage.

Automatic gain control is provided for line loss compensation.

DTMF

AMPLIFIER (PINS DTMF, LN AND RECO)

The TEA1099H has an asymmetrical DTMF input. The input impedance between DTMF and GND is 20 kΩ (typ.). The voltage gain between pins DTMF and LN is set to 25.35 dB. Without limitation from the output, the input stage can accommodate signals up to 180 mV (RMS) at room temperature for 2% of THD.

When the DTMF amplifier is enabled, dialling tones may be sent on the line. These tones can be heard in the earpiece or in the loudspeaker at a low level. This is called the confidence tone. The voltage attenuation between pins DTMF and RECO is typically equal to −16.5 dB.

The DC biasing of this input is 0 V. The automatic gain control has no effect on these

channels.

UXILIARY TRANSMIT AMPLIFIER (PINS TXAUX AND LN)

The TEA1099H has an asymmetrical auxiliary input TXAUX. The input impedance between TXAUX and GND is 20 kΩ (typ.). The voltage gain between pins TXAUX and LN is set to 12.5 dB. Without limitation from the output, the input stage can accommodate signals up to 1.2 V (RMS) at room temperature for 2% of THD. The TXAUX input is biased at two diodes voltage.

Automatic gain control is provided for line loss compensation.

ANDSFREE TRANSMIT OUTPUT STAGE (PINS HFTX AND LN)

The TEA1099H has an asymmetrical HFTX input, which is mainly intended for use in combination with the TXOUT output. The input impedance between HFTX and GND is 20 kΩ (typ.). The voltage gain between pins HFTX and LN is set to 34.7 dB. Without limitation from the output, the input stage can accommodate signals up to 95 mV (RMS) at room temperature for 2% of THD. The HFTX input is biased at two diodes voltage.

Automatic gain control is provided for line loss compensation.

ICROPHONE MONITORING ON TXOUT (PINS MIC+, MIC−

AND TXOUT)

The voltage gain between the microphone inputs MIC+/MIC− and the output TXOUT is set to 49.8 dB. This channel gives an image of the signal sent on the line while speaking in the handset microphone. Using external circuitry, this signal can be used for several purposes such as sending dynamic limitation or anti-howling in a listening-in application. The TXOUT output is biased at two diodes voltage.

The automatic gain control has no effect on these channels.

Receive channels (pins IR, RAUX, RECO, GARX and QR)

AMPLIFIER (PINS IR AND RECO)

The receive amplifier has one input IR which is referred to the line. The input impedance between pins IR and LN is 20 kΩ (typ.) and the DC biasing between these pins is equal to one diode voltage. The gain between pins IR (referred to LN) and RECO is typically equal to 29.7 dB. Without limitation from the output, the input stage can accommodate signals up to 50 mV (RMS) at room temperature for 2% of THD.

This receive amplifier has a rail-to-rail output RECO, which is designed for use with high ohmic (real) loads (larger than 5 kΩ). This output is biased at two diodes voltage.

Automatic gain control is provided for line loss compensation.

1999 Apr 08 11

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

EARPIECE AMPLIFIER (PINS GARX AND QR) The earpiece amplifier is an operational amplifier having

its output (QR) and its inverting input (GARX) available. Its input signal comes, via a decoupling capacitor, from the receive RECO output. It is used in combination with two resistors to get the required gain or attenuation compared to the receive gain. It can be chosen between

−3 and +15 dB. Two external capacitors C

GAR

(connected between GARX

and QR) and C

GARS

(connected between GARX and

GND) ensure stability. The C

GAR

capacitor provides a 1st-order low-pass filter. The cut-off frequency corresponds to the time constant C

GAR

× Re2.

The relationship C

GARS

≥ 10 × C

GAR

must be fulfilled.

The earpiece amplifier has a rail-to-rail output QR, biased at two diodes voltage. It is designed for use with low ohmic (real) loads (150 Ω) or capacitive loads (100 nF in series with 100 Ω).

UXILIARY RECEIVE AMPLIFIER (PINS RAUX AND RECO)

The auxiliary receive amplifier has an asymmetrical input RAUX; it uses the RECO output. Its input impedance between pins RAUX and GND is typically equal to 20 kΩ. The voltage gain between pins RAUX and RECO is equal to−2.4 dB. Without any limitation from the output, the input stage can accommodate signals up to 0.95 V (RMS) at room temperature for 2% of THD.

This auxiliary amplifier has a rail-to-rail output RECO, which is designed for use with high ohmic (real) loads (larger than 5 kΩ). This output is biased at two diodes voltage.

The automatic gain control has no effect on this channel.

Auxiliary ampliﬁers using AUXO (pins MIC+, MIC−, HFTX, IR and AUXO)

The TEA1099H has an auxiliary output AUXO, biased at two diodes voltage. This output stage is a rail-to-rail one, designed for use with high ohmic (real) loads (larger than 5kΩ). The AUXO output amplifier is used in three different channels, two transmit channels and one receive channel.

UXILIARY AMPLIFIERS USING THE MICROPHONE INPUTS

(PINS MIC+, MIC− AND AUXO) The auxiliary transmit amplifier using the microphone

MIC+ and MIC− inputs has a gain of 25.5 dB referenced to AUXO. Without limitation from the output, the input stage can accommodate signals up to 16 mV (RMS) at room temperature for 2% of THD.

The automatic gain control has no effect on this channel.

UXILIARY AMPLIFIERS USING HFTX

(

PINS HFTX AND AUXO)

The auxiliary transmit amplifier using the HFTX input has a gain of 15.2 dB referenced to AUXO.

The automatic gain control has no effect on this channel.

AMPLIFIER USING IR (PINS IR AND AUXO)

The auxiliary receive amplifier uses pin IR as input. The input is referred to LN and the DC biasing between these two pins is one diode voltage. The voltage gain between the input IR (referenced to LN) and the output AUXO is typically equal to 32.8 dB, which compensates typically the attenuation provided by the anti-sidetone network.

Automatic gain control is provided for line loss compensation.

AGC (pin AGC)

The TEA1099H performs automatic line loss compensation, which fits well with the true line attenuation. The automatic gain control varies the gain of some transmit and receive amplifiers in accordance with the DC line current. The control range is 6.45 dB for G

v(MIC-LN)

v(IR-RECO)

and G

v(IR-AUXO)

and 6.8 dB for the other affected channels, which corresponds approximately to a line length of 5.5 km for a 0.5 mm twisted-pair copper cable.

To enable this gain control, the AGC pin must be shorted to pin LN. The start current for compensation corresponds to a line current equal to typically 23 mA and the stop current to 57 mA. The start current can be increased by connecting an external resistor between pins AGC and LN. It can be increased up to 40 mA (using a resistor typically equal to 80 kΩ). The start and stop current will be maintained in a ratio equal to 2.5. By leaving the AGC pin open-circuit, the gain control is disabled and no line loss compensation is performed.

1999 Apr 08 12

Philips Semiconductors Product speciﬁcation

Speech and handsfree IC with auxiliary inputs/outputs and analog multiplexer

TEA1099H

Handsfree application

As can be seen from Fig.3, a loop is formed via the sidetone network in the line interface part and the acoustic coupling between loudspeaker and microphone of the handsfree part. When this loop gain is greater than 1, howling occurs. In a full duplex application, this would be the case. The loop-gain has to be much lower than 1 and therefore has to be decreased to avoid howling. This is achieved by the duplex controller. The duplex controller of the TEA1099H detects which channel has the ‘largest’ signal and then controls the gain of the microphone amplifier and the loudspeaker amplifier so that the sum of the gains remains constant.

As a result, the circuit in this handsfree application can be in three stable modes:

1. Transmit mode (TX mode). The gain of the microphone amplifier is at its maximum

and the gain of the loudspeaker amplifier is at its minimum.

2. Receive mode (RX mode). The gain of the loudspeaker amplifier is at its

maximum and the gain of the microphone amplifier is at its minimum.

3. Idle mode. The gain of the amplifiers is halfway between their

maximum and minimum value.

The difference between the maximum gain and minimum gain is called the switching range.

ANDSFREE MICROPHONE CHANNEL: PINS TXIN, GATX,

TXOUT

AND GNDTX (see Fig.7)

The TEA1099H has an asymmetrical handsfree microphone input TXIN with an input resistance of 20 kΩ. The DC biasing of the input is 0 V. The gain of the input stage varies according to the mode of the TEA1099H. In the transmit mode, the gain is at its maximum; in the receive mode, it is at its minimum and in the Idle mode it is halfway between maximum and minimum.

Switch-over from one mode to the other is smooth and click-free. The output TXOUT is biased at two diodes voltage and has a current capability equal to 20 µA (RMS). In the transmit mode, the overall gain of the microphone amplifier (from pins TXIN to TXOUT) can be adjusted from 0 up to 31 dB to suit specific application requirements. The gain is proportional to the value of R

GATX

and equals

15.2 dB with R

GATX

= 30.1 kΩ. Without limitation from the output, the microphone input stage can accommodate signals up to 18 mV (RMS) at room temperature for 2% of THD.

Fig.6 Handsfree telephone set principles.

handbook, full pagewidth

MGM299

DUPLEX

CONTROL

HYBRID

telephone

line

sidetone

acoustic coupling

+ 28 hidden pages