Datasheet TEA7540FP Datasheet (SGS Thomson Microelectronics)



NOISE/SPEECH DISCRIMINATION IN EMIS­SION ANDRECEPTION

INTEGRATED SIGNAL GAIN COMPRESSOR
IN BOTHMODES

PROGRAMMABLE ATTENUATORS IN BOTH
MODES

ADAPTED TO ACOUSTIC PARAMETERS OF
ALL CABINETS

LOW OPERATINGVOLTAGE2.5V
LOW OPERATINGCURRENT 2.1mA
CHIP SELECT BETWEEN HANDSFREE AND

MONITORINGMODES

TEA7540

HANDSFREECONTROLLER

SO28

DESCRIPTION

This 28 pins IC is an innovativeapproach to quality
handsfreetelephonesets.Itresultsfromanextensive
researchonspeechsignal.

PIN CONNECTION

(topview)

HYST1 ATR
HYST2

MICOUT

GND

CS

OUTE

ATTE

TIM

CCE

CE3
CE2
CE1

INE

VREF

1
2
3
4
5
6
7
8
9
10
11
12
13
14

ORDERING NUMBERS:

28
27
26
25
24

22
21
20
19
18
17
16
15

V+
IREF
OUTR
ATTR

VOL23
AMP SUP
AMP IN
CCR
CR3
CR2
CR1
RECOUT
INR

TEA7540FP

D93TL005

July 1998

T is advanced informationon a new product now indevelopment or undergoing evaluation. Details are subject to change without

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TEA7540

BLOCK DIAGRAM

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PIN FUNCTION

N° Name Function

1 GND Ground
2 CS Chip Select
3 OUTE Transmit Attenuator Output
4 ATTE Transmit Attenuator Input
5 HYST1 Transmit Channel Hysteresis
6 HYST2 Receive Channel Hysteresis
7 TIM RC Timer
8 CCE Time Constant of the Transmit Signal Compressor

9 CE3 Transmit Background Noise Memorization Output
10 CE2 Transmit Peak Detector Output
11 CE1 Transmit Rectifier Input
12 MICOUT Transmit Signal Compressor Output
13 INE Transmit Signal Compressor Input
14 V

15 INR Receive Signal Compressor Input

16 RECOUT Receive Signal Compressor Output
17 CR1 Receive Rectifier Input
18 CR2 Receive Peak Detector Output
19 CR3 Receive Background Noise Memorization Output
20 CCR Time Constant of the Receive Signal Compressor
21 AMP IN Handset Preamplifier Input
22 AMP SUP Handset Preamplifier Power Supply
23 VOL Volume Control
24 ATR Attenuation Value
25 ATTR Receive Attenuator Input
26 OUTR Receive Attenuator Output
27 I
28 V+

ref

ref

V+/2 - Reference Voltage

Reference Current Source

TEA7540

FUNCTIONAL DESCRIPTION

SWITCHEDATTENUATORS
Fig.A represents a block diagram of a handsfree
subset with attenuators in signal mode. To pre­vent the system from howling, the total loop gain,
including acoustic feedback through the housing
and sidetone coupling, must be less than 0dB.
For this purpose, two switchedattenuatorsare in­serted in each mode (emission and reception).
The attenuation is shifted from one mode to the
other, resulting from the speech level comparison
between each way.
To prevent the circuit to switch continuously in
one way, the operation of the IC must be fully
symetrical in both ways. This involves signal com­parison, attenuationvalue.

GAIN COMPRESSOR
In TEA7540, two signal compressors are inserted
in each mode before the signal comparison, so

the signal coming from each end has the same
level (100mV peak), the losses in each way (for
instance losses resulting from the line length in
receiving mode) are compensatedand the signal
comparison is fully symetrical. The time constant
of each signal compressor decreases 80 times
more quickly than it increases to prevent from
noise increasing between words. The compress­ing depth is 38dB.

BACKGROUND NOISEDISCRIMINATION
An additional feature provided in TEA7540 is
background noise level discrimination in each
way. The IC stores the background sound level
with a long time constant (3 to 5 seconds depend­ing on an external RC) and compares it with the
incoming signal in order to distinguish a useful
signal (speech) from the background noise. This
background noise memorization is also used to
compensatethe noise in each mode before signal
comparison: the noise level in each mode is sub-

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TEA7540

stracted from the incoming signal before the com­parison. So very high noise level in one mode
cannot troublethe comparisonbetween the useful
signals.
The result of the comparisonmanages the attenu­ators in the following way:

- The maximum attenuation is switched on
the mode where the speech signal is the
lowest. The maximum attenuation is fixed
by two external resistor (maximum 52dB).

Figure A

The time constant of the switch is fixed by
the timer via an externalcapacitor.

- When neither party is talking both attenu­ators are set to a medium attenuation.
Thus each mode is in idle mode. The time
constant of the switch from active mode to
idle mode must be long enough to prevent
from switching to idle mode between two
words (see fig.B). This time constant is
fixed by an externalRC.

Figure B

SPEECH/NOISE

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Em Rec

A max dB

1

0

1

0

0dB

IDLE (A max/2)

D93TL009A

TEA7540

TEA7540OPERATION

TEA7540 is powered through an external shunt
regulator (for instance the shunt regulator of the
monitor amplifier TEA7532) or an external zener
diode.
It can work at a very low voltage (2.5V) over the
circuit and it has a low current consumption
(2.1mA).
It’s also possible via the chip select pin (CS) to

Figure C:

ApplicationDiagram (Example of high range telephoneset using TEA7540).

put the handsfree function in standby to use the
circuit in monitoring mode with the handset micro­phone.
TEA7540 is designed to work with all kind of mi­crophone,including Electret.
TEA7540 also handles the handset microphone
signal (AMP IN) when the system is set to normal
conversationmode.

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

+

V

Top Operating Temperature -20 to 70

T

stg

Supply Voltage 12 V

Storage Temperature Range -65 to 125

°
°

C
C

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TEA7540

ELECTRICALCHARACTERISTICS (Refertotestcircuits,T

=25°C;V+=3V;f=1KHzunless otherwise

amb

specified).

Symbol Parameter Test Condition Min. Typ. Max. Unit Fig.
SUPPLY SECTION

+

V

I

TRANSMIT SECTION

COMPRESSOR

Rine Compressor input impedance PIN13 7.5 10.0 14.5 KΩ 1

C

G

1max

G

1min

V

T

I

cce1

I

cce2

V

cce1

V

cce2

PEAK DETECTOR

R

I

ce2

NOISE MEMORIZATION

V1 Maxvoltage drop on pin 9 33 36 45 mV 8

ATTENUATOR

R

ATE- Attenuation=

ATE-active Mode: Active Rpin24 = 11K
ATE-IDLE Mode: Noise Tx, Rx Comp.

RECEIVE SECTION

COMPRESSOR

R

C

G

2max

G

2min

V

micout

R

I

ccr1

I

ccr2

V

ccr1

V

ccr2

Supply Voltage 2.5 7.0 V 1
Current Consumption Vcs = 0

C

Handsfree mode

2.1

3.0
Vcs= N.C.
Monitoring mode

Compressor Range 16.5 dB

R

1.1

1.5

Maximum Gain 40.5 41.5 42.5 dB 2
Minimum Gain 24.0 25.0 26.0 dB 3
Output Voltage PIN12 compressingrange 160 200 240 mVpp 4

O

Transmit Distortion 3.0 % 4

dh

Compressor dacay timecurrent Increasing gain 1.0 1.25 1.5
Compressor rise time current Decreasing gain 65 85 105
Voltage drop PIN8

V

= Vref - Vpin8

cce

Input impedance PIN11 7.5 10.0 14.5 K

inpd

G1max 0 20 mV 2
G1min 175 225 275 mV 3

Rise time current 16 20 24

Input impedance PIN4 7.5 10 14.5 K

ina

20log(Voute/Vatte)

Rpin24 = 11K
Rpin24 = 15KΩ

Ω

46

58
Mode: Inactive Tx, Rx
Comp. Max Gain

0 1.5 3 dB 10

23 dB 11

Rpin24 = 11K

Ω
Ω

Max Gain

Input impedance PIN15 7.5 10.0 14.5 K

inr

Compressor Range 20.5 dB

R

Maximum Gain 35.5 36.5 37.5 dB 2
Minimum Gain 15.0 16.0 17.0 dB 3
Compressor output voltage PIN16 compressing range 160 200 240 mVpp 4
Receive Distortion 3.0 % 4

dh

Compressordecaytime

Increasing gain 1.0 1.25 1.5 µA5

current
Compressor rise time current Decreasing gain 65 85 105
Voltage drop P IN20

Vccr = Vref - Vpin20

G2max 0 20 mV 2
G2min 175 225 275 mV 3

mA
mA

A5

µ

A6

µ

Ω

A7

µ

Ω

dB
dB

Ω

A6

µ

1

1

1
9

1

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TEA7540

ELECTRICALCHARACTERISTICS (continued)

Symbol Parameter Test Condition Min. Typ. Max. Unit Fig.

PEAK DETECTOR

R

I

cr2

NOISE MEMORIZATION

V1 Maxvoltage drop on PIN 19 33 36 45 mV 8

ATTENUATOR

Rina Input impedance PIN25 7.5 10 14.5 KΩ 1

ATR- Attenuation=20lg(Voutr/Vatte)

ATR-active Mode: Active Rpin24 = 11K
ATR-IDLE Mode: Noise RX, TX Comp.

ATTENUATION CONTROL SECTION

V

TIME

I

TIME

V

TIMR

I

TIMR

ATRVOL Volume Control 29 32 35 dB 14

MICROPHONE PREAMPLIFIER

R

amp

G
G

Input impedance PIN17 7.5 10 14.5 K

inpd

Rise time current 16 20 24

Mode: Inactive RX, TX

Rpin24 = 11KΩ
Rpin24 = 15K

Ω

46

58
Comp. Max Gain

0 1.5 3 dB 10

23 dB 11

Rpin24 = 11K

Ω
Ω

Max Gain

Tx Mode Att.Voltage 190 250 325 mV 12
TX Mode Att.Current 40 50 70
RX Mode Att.Voltage -325 -250 -190 mV 13
RX Mode Att.Current 40 50 70

Imput impedance PIN21 35 50 70 K
V

mic
2off

= Voute-Vamp in Vcsopen 19 20 21 dB

mic

Compressor Gain
Monitoring Mode
G2 = V

recout/Vinr

Rext between PINs 2 - 28
Rext = open
Rext = 40K

Ω

36.5
16

Ω

A7

µ

dB
dB

A12

µ

A13

µ

Ω

dB
dB

1

9

Figure 1:

BasicConfiguration

Figure2:

V+=3V
pin 7 is forced to transmit mode
pin 11 is forcedto max gain
Input signal on pin 13 VINE= 1.5mVpp
output voltage VMICOUT measured on pin 12

TestConfiguration

G1max = 20log (VMICOUT / VINE)

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TEA7540

Figure 3: Test Configuration

V+=3V
pin 7 is forced to transmit mode
pin 11is forced to minimum gain
Input signal on pin 13 VINE = 1.5mVpp
output voltage VMICOUT measured on pin 12

G1min = 20log (VMICOUT / VINE)

Figure4: Test Configuration

V+=3V
pin 7 is forced to transmit mode
Input signal on pin 13 VINE in the compressing range (5mVpp for
example)
output voltage VMICOUT measured on pin 12

Figure 5:

V+=3V
pin 7 is forced to transmit mode
pin 11is forced to maximum gain

TestConfiguration

Figure6: Test Configuration

V+=3V
pin 7 is forced to transmit mode
pin 11 is forcedto minimum gain

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TEA7540

Figure 7: Test Configuration

V+=3V
pin 7 is forced to transmit mode
pin 11is forced to minimum gain

Figure8: Test Configuration

V+=3V
pin 7 is forced to transmit mode
pin 11 is forcedto minimum gain

Figure 9: Test Configuration

V+=3V
pin 7 is forced to receive mode
pin 11and pin 17 are forced to maximum gain
Input signal on pin 4 VATTE = 200mVpp

ATE2 = 20log (VOUTE / VATTE) with Rpin24 = 11KΩ

Figure10:

V+=3V
pin 7 is forced to transmit mode
Input signal on pin 4 VATTE = 200mVpp

ATE = 20log(VOUTE / VATTE)

TestConfiguration

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TEA7540

Figure 11: TestConfiguration

V+=3V
pin 7 is forced to idle mode after that the two compressor have been
forced at maximum gain by V11 and V17
Input signal on pin 4 VATTE = 200mVpp
Rpin24 = 11K

ATE6 = 20log(VOUTE / VATTE)

Ω

Figure12: TestConfiguration

V+=3V
pin 11 is forcedto 100mV to force the transmit mode

VTIM_E voltage on pin 7
ITIM_E current through the mA

Figure 13: TestConfiguration

V+=3V
pin 17is forced to 100mV toforce the receive mode

VTIM_R voltage on pin 7
ITIM_R current through the mA

Figure14: TestConfiguration

V+=3V
pin 7 is forced to receive mode
Input signal pin 25: VATTR = 200mVpp
Rpin23 = 9KΩ

ATRVOL = 20log(VOUTR/ VATTR)

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SO28 PACKAGEMECHANICAL DATA

TEA7540

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

A 2.65 0.104

a1 0.1 0.3 0.004 0.012

b 0.35 0.49 0.014 0.019

b1 0.23 0.32 0.009 0.013

C 0.5 0.020

c1 45°(typ.)

D 17.7 18.1 0.697 0.713

E 10 10.65 0.394 0.419
e 1.27 0.050

e3 16.51 0.65

F 7.4 7.6 0.291 0.299
L 0.4 1.27 0.016 0.050

mm inch

S8

(max.)

°

0016572

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TEA7540

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are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

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