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TEA7540
HANDSFREE CONTROLLER
NOISE/SPEECH DISCRIMINATION IN EMISSION AND RECEPTION INTEGRATED SIGNAL GAIN COMPRESSOR IN BOTH MODES PROGRAMMABLE ATTENUATORS IN BOTH MODES ADAPTED TO ACOUSTIC PARAMETERS OF ALL CABINETS LOW OPERATING VOLTAGE 2.5V LOW OPERATING CURRENT 2.1mA CHIP SELECT BETWEEN HANDSFREE AND MONITORING MODES
SO28 ORDERING NUMBERS: TEA7540FP
DESCRIPTION This 28 pins IC is an innovative approach to quality handsfree telephone sets. It results from an extensive research on speech signal. PIN CONNECTION (top view)
GND CS OUTE ATTE HYST1 HYST2 TIM CCE CE3 CE2 CE1 MICOUT INE VREF
1 2 3 4 5 6 7 8 9 10 11 12 13 14
D93TL005
28 27 26 25 24 23 22 21 20 19 18 17 16 15
V+ IREF OUTR ATTR ATR VOL AMP SUP AMP IN CCR CR3 CR2 CR1 RECOUT INR
July 1998
T
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is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without
TEA7540
BLOCK DIAGRAM
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PIN FUNCTION
N 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Name GND CS OUTE ATTE HYST1 HYST2 TIM CCE CE3 CE2 CE1 MICOUT INE Vref INR RECOUT CR1 CR2 CR3 CCR AMP IN AMP SUP VOL ATR ATTR OUTR Iref V+ Ground Chip Select Transmit Attenuator Output Transmit Attenuator Input Transmit Channel Hysteresis Receive Channel Hysteresis RC Timer Time Constant of the Transmit Signal Compressor Transmit Background Noise Memorization Output Transmit Peak Detector Output Transmit Rectifier Input Transmit Signal Compressor Output Transmit Signal Compressor Input V+/2 - Reference Voltage Receive Signal Compressor Input Receive Signal Compressor Output Receive Rectifier Input Receive Peak Detector Output Receive Background Noise Memorization Output Time Constant of the Receive Signal Compressor Handset Preamplifier Input Handset Preamplifier Power Supply Volume Control Attenuation Value Receive Attenuator Input Receive Attenuator Output Reference Current Source Function
FUNCTIONAL DESCRIPTION SWITCHED ATTENUATORS 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 switched attenuators are 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, attenuation value. 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 compensated and 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 NOISE DISCRIMINATION 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 compensate the noise in each mode before signal comparison: the noise level in each mode is sub3/12
TEA7540
stracted from the incoming signal before the comparison. So very high noise level in one mode cannot trouble the comparison between the useful signals. The result of the comparison manages 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 external capacitor. - 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 external RC.
Figure B
1 Em Rec 0
1 SPEECH/NOISE 0
0dB IDLE (A max/2)
A max dB
D93TL009A
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TEA7540
TEA7540 OPERATION 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 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 conversation mode.
Figure C: Application Diagram (Example of high range telephone set using TEA7540).
ABSOLUTE MAXIMUM RATINGS
Symbol V
+
Parameter Supply Voltage Operating Temperature Storage Temperature Range
Value 12 -20 to 70 -65 to 125
Unit V C C
Top Tstg
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ELECTRICAL CHARACTERISTICS (Refer to test circuits, Tamb = 25C; V+ = 3V; f = 1KHz unless otherwise specified).
Symbol SUPPLY SECTION V+ IC Supply Voltage Current Consumption Vcs = 0 Handsfree mode Vcs= N.C. Monitoring mode 2.5 2.1 1.1 7.0 3.0 1.5 V mA mA 1 1 Parameter Test Condition Min. Typ. Max. Unit Fig.
TRANSMIT SECTION COMPRESSOR Rine CR G1max G1min VO Tdh Icce1 Icce2 Vcce1 Vcce2 R inpd Ice2 V1 Rina ATECompressor input impedance Compressor Range Maximum Gain Minimum Gain Output Voltage Transmit Distortion Compressor dacay time current Compressor rise time current Voltage drop PIN8 Vcce = Vref - Vpin8 Input impedance PIN11 Rise time current Max voltage drop on pin 9 Input impedance PIN4 Attenuation= 20log(Voute/Vatte) Mode: Inactive Tx, Rx Comp. Max Gain Rpin24 = 11K Rpin24 = 15K Increasing gain Decreasing gain G1max G1min 175 7.5 16 33 7.5 1.0 65 1.25 85 0 225 10.0 20 36 10 46 58 PIN12 compressing range 40.5 24.0 160 PIN13 7.5 10.0 16.5 41.5 25.0 200 42.5 26.0 240 3.0 1.5 105 20 275 14.5 24 45 14.5 14.5 K dB dB dB mVpp % A A mV mV K A mV K dB dB 2 3 4 4 5 6 2 3 1 7 8 1 9 1
PEAK DETECTOR
NOISE MEMORIZATION ATTENUATOR
ATE-active Mode: Active ATE-IDLE Mode: Noise Tx, Rx Comp. Max Gain RECEIVE SECTION COMPRESSOR Rinr CR G2max G2min Vmicout Rdh Iccr1 Iccr2 Vccr1 Vccr2 Input impedance Compressor Range Maximum Gain Minimum Gain Compressor output voltage Receive Distortion Compressor decay time current Compressor rise time current Voltage drop PIN20 Vccr = Vref - Vpin20
Rpin24 = 11K Rpin24 = 11K
0
1.5 23
3
dB dB
10 11
PIN15
7.5 35.5 15.0
10.0 20.5 36.5 16.0 200 1.25 85 0 225
14.5 37.5 17.0 240 3.0 1.5 105 20 275
K dB dB dB mVpp % A A mV mV
1 2 3 4 4 5 6 2 3
PIN16 compressing range Increasing gain Decreasing gain G2max G2min
160 1.0 65 175
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ELECTRICAL CHARACTERISTICS (continued)
Symbol PEAK DETECTOR R inpd Icr2 V1 Rina ATRInput impedance Rise time current Max voltage drop on PIN 19 Input impedance Attenuation= 20lg(Voutr/Vatte) Mode: Inactive RX, TX Comp. Max Gain PIN25 Rpin24 = 11K Rpin24 = 15K Rpin24 = 11K Rpin24 = 11K 0 PIN17 7.5 16 33 7.5 10 20 36 10 46 58 1.5 23 3 14.5 24 45 14.5 K A mV K dB dB dB dB 1 7 8 1 9 Parameter Test Condition Min. Typ. Max. Unit Fig.
NOISE MEMORIZATION ATTENUATOR
ATR-active Mode: Active ATR-IDLE Mode: Noise RX, TX Comp. Max Gain ATTENUATION CONTROL SECTION VTIME ITIME VTIMR ITIMR ATRVOL Ramp Gmic G2off Tx Mode Att.Voltage TX Mode Att.Current RX Mode Att.Voltage RX Mode Att.Current Volume Control Imput impedance Vmic = Voute-Vamp in Compressor Gain Monitoring Mode G2 = Vrecout/Vinr
10 11
190 40 -325 40 29 PIN21 Vcs open Rext between PINs 2 - 28 Rext = open Rext = 40K 35 19
250 50 -250 50 32 50 20 36.5 16
325 70 -190 70 35 70 21
mV A mV A dB K dB dB dB
12 12 13 13 14
MICROPHONE PREAMPLIFIER
Figure 1: Basic Configuration
Figure 2: Test Configuration
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to max gain Input signal on pin 13 VINE = 1.5mVpp output voltage VMICOUT measured on pin 12 G1max = 20log (VMICOUT / VINE)
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TEA7540
Figure 3: Test Configuration Figure 4: Test Configuration
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to minimum gain Input signal on pin 13 VINE = 1.5mVpp output voltage VMICOUT measured on pin 12 G1min = 20log (VMICOUT / VINE)
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: Test Configuration
Figure 6: Test Configuration
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to maximum gain
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to minimum gain
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TEA7540
Figure 7: Test Configuration Figure 8: Test Configuration
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to minimum gain
V+ = 3V pin 7 is forced to transmit mode pin 11 is forced to minimum gain
Figure 9: Test Configuration
Figure 10: Test Configuration
V+ = 3V pin 7 is forced to receive mode pin 11 and pin 17 are forced to maximum gain Input signal on pin 4 VATTE = 200mVpp ATE2 = 20log (VOUTE / VATTE) with Rpin24 = 11K
V+ = 3V pin 7 is forced to transmit mode Input signal on pin 4 VATTE = 200mVpp ATE = 20log(VOUTE / VATTE)
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TEA7540
Figure 11: Test Configuration Figure 12: Test Configuration
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)
V+ = 3V pin 11 is forced to 100mV to force the transmit mode VTIM_E voltage on pin 7 ITIM_E current through the mA
Figure 13: Test Configuration
Figure 14: Test Configuration
V+ = 3V pin 17 is forced to 100mV to force the receive mode VTIM_R voltage on pin 7 ITIM_R current through the mA
V+ = 3V pin 7 is forced to receive mode Input signal pin 25: VATTR = 200mVpp Rpin23 = 9K ATRVOL = 20log(VOUTR / VATTR)
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TEA7540
SO28 PACKAGE MECHANICAL DATA
DIM. MIN. A a1 b b1 C c1 D E e e3 F L S 7.4 0.4 17.7 10 1.27 16.51 7.6 1.27 8 (max.) 0.291 0.016 18.1 10.65 0.1 0.35 0.23 0.5 45 (typ.) 0.697 0.394 0.050 0.65 0.299 0.050 0.713 0.419 mm TYP. MAX. 2.65 0.3 0.49 0.32 0.004 0.014 0.009 0.020 MIN. inch TYP. MAX. 0.104 0.012 0.019 0.013
0016572
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Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c) 1998 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
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