UTC L388 12 LINEAR INTEGRATED CIRCUIT VOICE-SWITCH CIRCUIT FOR HANDSFREE SPEAKERPHONE TAM SOP-16 DESCRIPTION The UTC L388 12 contains all the necessary circuitry, amplifiers, detectors, comparators and control functions to implement a high performance, voice-switched, ”hands-free” function in an answering machine. The UTC L 388 12 is designed for answering machines that are either powered from the telephone line or from a DIP-18 mains powered dc. supply. Filtering of both the audio and control signals in both transmitter and receiver channels possible. An external loudspeaker amplifier has to be used, normally the same as used for the answering machine. FEATURES *Settable gain dynamics (25 or 50dB) *Low power consumption, totally 1.0mA at 3.3V typical. *Background noise compensation in the transmitting channel *with hold function. *Excellent noise performance. *Both channel input amplifiers have balanced inputs. *Minimum of external components needed for function. PIN CONFIGURATION 18-pin DIP package 16-pin SO package CTR 1 16 GND -Txin 2 15 +V +Txin 3 14 -Rxin F2out 4 13 F5out Txout 5 12 Rxout TxDetin 6 11 RxDetin TxDetout 7 10 RxDetout NDet 8 9 UTC CMP F2out 1 18 +Txin Txout 2 17 -Txin TxDetin 3 16 CTR TxDetout 4 15 NC N Det 5 14 GND CMP 6 13 +V RxDetout 7 12 -Rxin Rx Detin 8 11 +Rxin Rxout 9 10 UNISONIC TECHNOLOGIES CO. LTD F5out 1 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT PIN DESCRIPTIONS 16-pin SO 18-pin DIP SYMBOL DESCRIPTION 1 2 3 4 5 6 16 17 18 1 2 3 CTR -Txin +Txin F2out Txout TxDetin 7 4 TxDetout 8 5 NDet 9 6 CMP 10 7 RxDetout 11 12 13 14 8 9 10 11 12 RxDetin Rxout F5out +Rxin -Rxin 15 13 V+ 16 14 15 GND NC Control input for gain dynamics (25 or 50dB), mute and disable. Transmitter channel negative input. Input impedance 3kΩ. Transmitter channel positive input. Input impedance 100kΩ. Output of the second amplifier in the transmitter channel. Transmitter channel output. Min. ac load impedance 10kΩ. Input of the transmitter channel signal detector. Input impedance 13kΩ. Output of the transmitter channel signal detector. Goes negative referred to the internal ref. voltage of app.2V when a transmitter signal is present. Background noise detector output. Goes positive referred to the internal ref. Voltage of app.2V when a background noise signal is present. Comparator input.. Summing point to the different Detector outputs. Output of the receiver channel signal detector. Goes positive referred to the internal ref. Voltage of app.2V when a receiver signal is present Input of the receiver channel signal detector. Input impedance 13kΩ. Receiver channel output. Min. ac load impedance 10kΩ. Output of the second amplifier in the receiver channel. Receiver channel positive input. Input impedance 140kΩ. Receiver channel negative input,Input impedance 20kΩ. Supply of the speech switching circuitry. A shunt regulator, voltage apprx. 3.3V at 1.0mA. System ground. Not connected. BLOCK DIAGRAM(16-pin SO package) 1 5 12 16 Control F3 4 6 15 F6 + F5 F2 2 3 - F1 Ref. + 8 UTC 13 11 7 9 14 F4+ 10 UNISONIC TECHNOLOGIES CO. LTD 2 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT MAXIMUM RATINGS PARAMETER SYMBOL RATINGS UNIT ID 10 -0,5 ~ Vpin15+0.5 -20 ~ +70 -55 ~ +125 mA V ℃ ℃ Speech switch supply current Voltage Pin 1-14 Operating temperature Storage temperature Topr Tstg TEST CIRCUIT + V+ ID + VTxout RxDetin 11 ID 100nF 15 V+ V+ L388 12 GND RxDetout 10 16 GND 16 10μF Rxout 12 + 15 V+ 5 Txout L388 12 10μF + RF2out ITxin 4 F2out + 4.7μF + VTxin ISOLATION AND MEASUREMENT OF VRef CRX 10μF + F5out 13 1μF -Rx in + 3 +Txin 14 NDet TxDetout CMP RxDetout CTR 2 -Txin8 7 9 10 1 CTxDet 1μF 0.1μF CRxDet + + RCTR INDet VNDet ITxDet VTxDet VRout RRout RxDetin 11 6 TxDetin CTx F2out VRef 10μF RTxout 100μF/16V IRxin F5out RF5out VRxin IRxDet ICTR VCMP VRxDet VCTR ELECTRICAL CHARACTERISTICS (Ta=25℃,f=1kHz, RCTR=0,CTxDet=0,RTxout= ∞,RRXout= ∞,RF2out= ∞, RF5out= ∞,RTX=0,RRX=0,CRxDet=0 and ID=1.0mA unless otherwise noted) PARAMETER Speech control section Terminal voltage, V+ Internal reference voltage, VRef Frequency response for all amplifiers Transmit gain, 20·Iog(VTxout/VTxin) TEST CONDITIONS ID=1.0mA 200-3400Hz,Relative 1 kHz VCMP=VRef-0.1V VCMP=VRef+0.1V VCMP=VRef-0.1V RCTR=100k,VCTR=V+ VCMP=VRef+0.1V RCTR=100k,VCTR=V+ Receive gain, 20·Iog(VRxout/VRxin) VCMP=VRef+0.1V VCMP=VRef-0.1V VCMP=VRef+0.1V RCTR=100k,VCTR=V+ VCMP=VRef-0.1V RCTR=100k,VCTR=V+ Max transmit detector gain, VTxDet<200mVP ,CTX=100nF 20·Iog(VTxdet/VTxin) VCMP=VRef+0.1V VCMP=VRef-0.1V Max transmit detector gain, VRxDet<200mVP ,CTX=100nF 20·Iog(VRxdet/VRxin) VCMP=VRef+0.1V VCMP=VRef-0.1V Background noise rectifier gain,(note 1) VCMP=VRef-0.1V,Ctxdet=1μF VCMP=VRef+0.1V,Ctxdet=1μF UTC MIN UNISONIC TECHNOLOGIES TYP MAX 3.3 1.96 -1 41.5 41.5 26.5 26.5 37 22.5 1 44 -6 44 19 29 -21 29 4 -3.5 21.5 -18.5 6.5 67.5 42.5 UNIT V V dB dB dB dB dB dB dB dB dB dB dB 53 28 6.0 Hold dB dB dB CO. LTD 3 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT PARAMETER +TxIn input impedance -TxIn input impedance -RxIn input impedance Txout ac, load impedance Rxout ac, load impedance F2out ac, load impedance F5out ac, load impedance Transmitter channel output swing, VTXOut Receiver channel output swing, VRxOut Transmitter output noise, VTxOut Receiver output noise, VRxOut TxDet sink current, ITxDetOut RxDet source current, IRxDetOut TxDet source current, ITxDet RxDet sink current, IRxDetOut TxDet swing relative to VRef, VTxDetOut RxDet swing relative to VRef, VRxDetOut NDet sink current (fast charge), INDet NDet source current, INDet NDet Ieakage current(hold),INDet NDet swing relative to VRef,VNDet CMP(comparator) sensitivity, Transmit(Tx) mode to receive (Rx) mode or vice versa CTR voltage for 25 dB dynamics,VCTR CTR voltage for mute,ICTR CTR voltage for disable,VCTR TEST CONDITIONS MIN TYP MAX UNIT 80 2.4 16 10 10 10 10 100 3.0 20 120 3.6 24 kΩ kΩ kΩ kΩ kΩ kΩ kΩ 2% distortion, RTxout=RRxout=25 kΩ 2% distortion, RTxout=RRxout=25 kΩ VCMP=VRef-0.1V,vTXIn=0V VCMP=VRef+0.1V,vRXIn=0V VtxDetIn=VRef+0.1V VRxIn=VRef-0.1V VCMP=VRef-0.1V VRxDetIn=VRef+0.1V VTxDetIn=VRef+0.1V VRxDetIn=VRef-0.1V VTxDetIn=VRef-0.1V VCMP=VRef-0.1V VTxDetIn=VRef+0.1V VCMP=VRef+0.1V VTxDetIn=VRef-0.1V VCMP=VRef+0.1V VCMP=VRef-0.1V VTxDetIn=VRef+0.1V Tx mode=max Tx gain, Rx mode=max Rx gain VCMP=VRef+0.35V,RCTR=100kΩ 2.5 500 500 -75 -75 -6.0 6.0 -2.5 30 -30 (note 2) (note 2) 3 mVp mVp dBpsof dBA mA mA μA μA -0.7 +0.7 -4.5 -1.5 V V mA 5 7 μA -100 nA -0.45 V 50 100 V+ mV V μA VCMP=VRef+0.35V 0.55 V Notes: VNDet-VRef 1. 20· log ( ) VTxDet-VTxDetO VNDet=voltage at noise detector output VRef=reference voltage (about 1.9V) VTxDet=Voltage at transmit detector output VTxDetO=voltage at transmit detector at the point when the voltage at the noise detector starts moving when a signal at transmit channel input is gradually increased (threshold, typical value 30 mV) 2. Depends on V+. Channels are tracking. UTC UNISONIC TECHNOLOGIES CO. LTD 4 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT FUNCTIONAL DESCRIPTION SPEECH CONTROL SECTION Transmitter and Receiver Channels The transmitter and receiver channels consist of three amplifying stages each, F1,F2,F3 and F4,F5,F6.The inputs of the amplifiers must be ac. coupled because they are dc. vise at the internal reference voltage(≈2V) level. F1 and F4 are fixed gain amplifiers of 30,5 dB and 15.5 dB respectively, while the rest of them are of controlled gain type. The gain of F2,F3 as well as F5 and F6 is controlled by comparators. The comparator receives its information partly from the summing point of the transmitter, receiver and background noise detectors at CMP input and partly through the control input, CTR, which controls the gain dynamics (25 or 50 dB). Amplifiers F2 and F3 have the maximum gain when the transmitter channel is fully open, consequently the amplifiers F5 and F6 will have minimum gain and vice versa. See figure.1 and figure. 9. The positive input on transmitter and the negative input on receiver channel has a rather high input impedance. It renders a good gain precision and noise performance when used with low signal source impedance. The differential input of the transmitter channel can be used to suppress unwanted signals in the microphone supply, see figure. 5. Signal Detectors and Comparator The signal detectors sense and rectify the receiver and microphone signals to opposite polarities referenced to the internal reference voltage of approx. 2V.The voltage at RxDet will go positive and at TxDet negative in the presence of a signal at the respective channel input. In the idle(no signal) state, the voltages at RxDet, TxDet and CMP are equal to the internal reference voltage. Signal at Txin will result in an decreasing level at TxDetout and hence also at CMP input. the transmitter channel and decrease it in the receiver channel. Signal at Rxin will do vice versa. The voltages RxDetout and TxDetout controlthus the gain setting in respective channel through the comparators using the CMP input as a summing point with an input current of less than 1μA. The attack time in the receiver channel is set by C2 together with C1 and either by the maximum current capability of the detector output or it with R2 added. The transmitter channel works likewise. See figure.5. The decay time in the receiver and transmitter channels is set by C2 and C3 respectively. The resistor in the time constant is formed by an internal 200kΩresistor in parallel with the external resistors R3 and R4 respectively. The influence of eventual R1 and R2 can be omitted. The text above describes the case when only one channel is open at a time and there is a distinctive pause between signals at receiver and transmitter channel inputs so the circuit will have time to reach its idle state. See figure.10 A) to E). If one of the channels gets an input signal immediately after the signal has disappeared from the other channel input the effective decay time , as the CMP input sees it, will be shorter than in the first case. See figure.10 F) to G). The capacitor C4 at CMP -input sets the speed of the gain change in the transmitter and receiver channels. The capacitors C2 and C3 should be dimensioned for a charging time of 0.5-10mS and for a discharge time of 150-300mS. The question of switching times being a highly subjective proposition, is in large dependent of the language being spoken in the system , caused by the varying sound pressure picture of the different languages. A hysteresis effect is achieved in the switching since the level detectors sense the signals after F2 and F5 respectively (F2 and F5 are affected by the gain setting). For example: If the transmitter channel is open (maximum gain),a smaller signal at Txin is enough to keep the channel open than would be necessary to open it when the receiver channel is open. The output swing of the level detectors is matched for variations in the supply voltage. The detectors have a logarithmic rectifier characteristic whereby gain and sensitivity is high at small signals. There is a break point in the curve at a level of + 200mV from the internal reference voltage app.2V,where the sensitivity for increasing input signals decreases with factor of 10, increasing the detectors dynamic range. See figure.8. Background Noise Detector The general function of the background noise detector in the transmitting channel is to create a positive signal (in respect to the reference) so that, when coupled to the summing point at the CMP input, will counteract the signal from the transmitter level detector representing the actual sound pressure level at the microphone. This counteracts the noise from influencing the switching characteristics. The input signal to the background noise level detector is taken from the output of the transmitter detector, a voltage representing the envelope of the amplified microphone signal. The detector inverts and amplifies this signal 2 X (transmitting mode) and has on it is output a RC network consisting of an internal resistor of 100k and an external capacitor C4.The voltage across C4 is connected to the CMP input (summing point) via a resistor R5.The resistor R6 is important in order to keep the charging current of C4 within safe limits in regard of high charge peaks that could be audible in the system. The extent to which the NDet UTC UNISONIC TECHNOLOGIES CO. LTD 5 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT output will influence the potential at CMP input is set by the gain of the detector, the maximum swing and R5.If a continuous input signal is received from the microphone (>10sec.) the voltage across C4 is pulled negative(relative to the reference)with a time constant set by C4 to e.g.5 sec. A continuous input signal is thus treated as noise. Since the output of the noise detector is going negative it thereby counteracts the signal from the transmitter detector and thus helping the receiver detector signal to maintain a set relation to the transmitter detector signal If the transmitter input signal contains breaks like breath pauses the voltage at TxDetout decreases. If the voltage across C3 gets less than the inverted voltage across C4 divided by the detector gain a rapid charge of C4 towards reference will follow (all levels referred to the reference).If the breaks are frequent as in speech the background detector will not influence the switching characteristic of the system. See figure.9. There is a threshold of approx. 50mV at TxDetout to prevent the activation of background noise detection in noiseless environment. In the receiver mode some of the loudspeaker output signal will be sensed by the microphone. In order not to treat this input signal as noise, the noise detector goes into a hold state and “remembers” the level from the previous transmitting mode periode. CTR Input For full speech control (50dB attenuation between the channels) this input can be left unconnected. To set the function to 25dB attenuation the input has to be higher than 600mV below V+. See figure 11. To set the circuit into a mute state(results in, reduced gain in receiver channel for the DTMF confidence tone in the loudspeaker and closed transmitter channel) a voltage below Vref has to be connected to the input. By lowering the voltage at the input below 0.9V a condition will emerge where both receiver and transmitter channels are closed. See figure.4 and 9. CTR Txout V+ 1 5 12 L388 12 16 Control F3 4 6 15 F6 +Txin 2 F2 13 11 + - 3 +F1 F4 - Ref. 8 7 NDet R5 + 100k F5 F2 -Txin L388 12 Rxout GND C4 14 2 Rxi n C3 C1 + 120k 20k 14 3k Figure 2. Receiver and transmitter channel input arrangement Power amplifier input Transmitter channel output CTR 1 Txout 5 L388 12 C +L C + + R 13 11 16 GND Receiver input F5 R -Txin C P1 F6 F2 2 +Txin C Mic. 12 Rxout C + C C R Control F3 4 6 15 R Rx VRxin C2 Figure 1. Passive networks setting the speech control function R 120k F4 + - VTxin TxDet CMP PxDet + F5 16 10 9 100k I 3k 3 Tx F1 + - Ref. 3 - F1 + Ref. 8 NDet 7 9 TxDet CMP F4 - 14 10 Rxin C PxDet C C4 + R5 + C3 C1 + R C2 Figure 3. Speech switching arrangement UTC UNISONIC TECHNOLOGIES CO. LTD 6 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT L388 12 ID=1mA 15 +V The circuit has a buit in shunt voltage generator.It needs a minimum 1mA current for its function.The voltage at this current will be 3.3V.If the voltage +V is not constant care must be taken so that the I D will not exeed 10 mA + Figure 4. Circuit supply function VRxDet + +600 F2 R4 R7 C2 R6 R5 C1 R1=R2=3k R3=R4=100k R5=R6 C1=C2 Mic. Ref. +400 F1 R3 - + +200 R2 2 R1 3 2.5 Vref=2V 16 7.5 1.0 0.5 -200 VRxin mV p VTxin 10 1.5 -400 C3 C4 5.0 Vref -600 VTxDet Figure 5. Transmitter channel input amplifier used to suppress ripple in the mic.supply.(CMRR). Figure 6. Transmitter and receiver channel rectifier characteristics. VRxout (mV) VTxout (mV) TxDetout NDet 500 500 400 400 300 300 200 200 100 100 ~ ~ V+(V) dB Receive gain= Transmit gain= Figure 8. Transmitter and receiver channel output dynamics. dB 30 40 20 30 20 VCTR=V+ VCTR=V+ Rxdet Txdet 10 A E Full recieve level B 0 10 0 2.4 2.6 2.8 3.0 3.2 3.4 2.4 2.6 2.8 3.0 3.2 3.4 Figure 7. Relationship in timing between the voltage levels at TxIN,TxDet and NDet VCTR=open VCTR=open -20 -20 0 20 F G D CMP Full transmit level 40 60 VCMP - VREF mV Figure 9. Transmit and reveive gain as a function of VCMP and VCTR UTC C -10 VCTR = VREF -60 -40 V+(V) ~ ~ Txin Figure 10. Timing of the transmitter and receiver channels at the CMP-input UNISONIC TECHNOLOGIES CO. LTD 7 QW-R108-013,A UTC L388 12 LINEAR INTEGRATED CIRCUIT Mode Vref 25 dB speech control 50 dB speech control DTMFMute Total mute 2 3 0 1 Figure 11. Control modes as function of voltage applied to gain dynamics control input CTR;ID=1mA UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UTC UNISONIC TECHNOLOGIES CO. LTD 8 QW-R108-013,A