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 1 28 V+ CS 2 27 IREF OUTE 3 26 OUTR ATTE 4 25 ATTR HYST1 5 24 ATR HYST2 6 23 VOL TIM 7 22 AMP SUP CCE 8 21 AMP IN CE3 9 20 CCR CE2 10 19 CR3 CE1 11 18 CR2 MICOUT 12 17 CR1 INE 13 16 RECOUT VREF 14 15 INR D93TL005 July 1998 T 1/12 is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without TEA7540 BLOCK DIAGRAM 2/12 TEA7540 PIN FUNCTION N° Name Function 1 GND 2 CS 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 Ground Chip Select 9 CE3 Transmit Background Noise Memorization Output 10 CE2 Transmit Peak Detector Output 11 CE1 Transmit Rectifier Input 12 MICOUT 13 INE Transmit Signal Compressor Input 14 Vref V+/2 - Reference Voltage 15 INR Receive Signal Compressor Input 16 RECOUT 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 22 AMP SUP 23 VOL Volume Control 24 ATR Attenuation Value 25 ATTR Receive Attenuator Input 26 OUTR Receive Attenuator Output 27 Iref Reference Current Source 28 V+ Transmit Signal Compressor Output Receive Signal Compressor Output Handset Preamplifier Input Handset Preamplifier Power Supply 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). 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 A Figure B 1 Em Rec 0 1 SPEECH/NOISE 0 0dB IDLE (A max/2) A max dB 4/12 D93TL009A 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 + Parameter Unit 12 V Top Operating Temperature -20 to 70 °C Tstg Storage Temperature Range -65 to 125 °C V Supply Voltage Value 5/12 TEA7540 ELECTRICAL CHARACTERISTICS (Refer to test circuits, Tamb = 25°C; V+ = 3V; f = 1KHz unless otherwise specified). Symbol Parameter Test Condition Min. Typ. Max. Unit Fig. 7.0 V 1 2.1 3.0 mA 1.1 1.5 mA 10.0 14.5 KΩ SUPPLY SECTION V+ Supply Voltage IC Current Consumption 2.5 Vcs = 0 Handsfree mode Vcs= N.C. Monitoring mode 1 TRANSMIT SECTION COMPRESSOR Rine CR Compressor input impedance PIN13 7.5 Compressor Range 16.5 1 dB G1max Maximum Gain 40.5 41.5 42.5 dB 2 G1min Minimum Gain 24.0 25.0 26.0 dB 3 160 200 240 mVpp 4 3.0 % 4 VO Output Voltage Tdh Transmit Distortion Icce1 Compressor dacay time current Increasing gain 1.0 1.25 1.5 µA 5 Icce2 Compressor rise time current Decreasing gain 65 85 105 6 Vcce1 Voltage drop PIN8 Vcce = Vref - Vpin8 0 20 µA mV G1min 175 225 275 mV 3 Input impedance PIN11 7.5 10.0 14.5 KΩ 1 Rise time current 16 20 24 µA 7 33 36 45 mV 8 10 14.5 KΩ 1 dB dB 9 Vcce2 PIN12 compressing range G1max 2 PEAK DETECTOR R inpd Ice2 NOISE MEMORIZATION V1 Max voltage drop on pin 9 ATTENUATOR Rina Input impedance PIN4 ATE- Attenuation= 20log(Voute/Vatte) Mode: Inactive Tx, Rx Comp. Max Gain 7.5 Rpin24 = 11KΩ Rpin24 = 15KΩ ATE-active Mode: Active Rpin24 = 11KΩ ATE-IDLE Mode: Noise Tx, Rx Comp. Max Gain Rpin24 = 11KΩ 46 58 0 1.5 3 23 dB 10 dB 11 KΩ 1 RECEIVE SECTION COMPRESSOR Rinr Input impedance CR Compressor Range G2max Maximum Gain G2min Minimum Gain Vmicout Compressor output voltage Rdh Receive Distortion Iccr1 Compressor decay time current Iccr2 Vccr1 Vccr2 6/12 PIN15 7.5 10.0 14.5 20.5 PIN16 compressing range dB 35.5 36.5 37.5 dB 2 15.0 16.0 160 200 17.0 dB 3 240 mVpp 4 3.0 % 4 Increasing gain 1.0 1.25 1.5 µA 5 Compressor rise time current Decreasing gain 65 85 105 G2max 0 20 µA mV 6 Voltage drop PIN20 Vccr = Vref - Vpin20 225 275 mV 3 G2min 175 2 TEA7540 ELECTRICAL CHARACTERISTICS (continued) Symbol Parameter Test Condition Min. Typ. Max. Unit Fig. 7.5 10 14.5 KΩ 1 16 20 24 µA 7 33 36 45 mV 8 10 14.5 KΩ 1 dB dB 9 PEAK DETECTOR R inpd Input impedance Icr2 Rise time current PIN17 NOISE MEMORIZATION V1 Max voltage drop on PIN 19 ATTENUATOR Rina Input impedance PIN25 ATR- Attenuation= 20lg(Voutr/Vatte) Mode: Inactive RX, TX Comp. Max Gain Rpin24 = 11KΩ Rpin24 = 15KΩ ATR-active Mode: Active Rpin24 = 11KΩ ATR-IDLE Mode: Noise RX, TX Comp. Max Gain Rpin24 = 11KΩ 7.5 46 58 0 1.5 3 dB 10 dB 11 325 mV 12 µA mV 12 13 23 ATTENUATION CONTROL SECTION VTIME Tx Mode Att.Voltage 190 250 ITIME TX Mode Att.Current 40 50 70 VTIMR RX Mode Att.Voltage -325 -250 -190 ITIMR RX Mode Att.Current 40 50 70 Volume Control 29 32 35 µA dB ATRVOL 13 14 MICROPHONE PREAMPLIFIER Ramp Imput impedance PIN21 35 50 70 KΩ Gmic Vmic = Voute-Vamp in Vcs open 19 20 21 dB G2off Compressor Gain Monitoring Mode G2 = Vrecout/Vinr Rext between PINs 2 - 28 Rext = open Rext = 40KΩ Figure 1: Basic Configuration 36.5 16 dB dB 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) 7/12 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 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 G1min = 20log (VMICOUT / VINE) 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 8/12 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 V+ = 3V pin 7 is forced to transmit mode Input signal on pin 4 VATTE = 200mVpp ATE = 20log(VOUTE / VATTE) ATE2 = 20log (VOUTE / VATTE) with Rpin24 = 11KΩ 9/12 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 = 11KΩ 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 ATE6 = 20log(VOUTE / VATTE) Figure 13: Test Configuration Figure 14: Test Configuration V+ = 3V pin 17 is forced to 100mV to force the receive mode V+ = 3V pin 7 is forced to receive mode Input signal pin 25: VATTR = 200mVpp Rpin23 = 9KΩ VTIM_R voltage on pin 7 ITIM_R current through the mA ATRVOL = 20log(VOUTR / VATTR) 10/12 TEA7540 SO28 PACKAGE MECHANICAL DATA mm DIM. MIN. TYP. A inch MAX. MIN. TYP. 2.65 MAX. 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 S 8° (max.) 0016572 11/12 TEA7540 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. 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