LS656AD1 STMICROELECTRONICS | Alldatasheet

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{77 SGS-THOMSON , MICROELECTRONICS LS656 TELEPHONE SPEECH CIRCUIT WITH MULTIFREQUENCY TONE GENERATOR INTERFACE « PRESENTS THE PROPER DC PATH FOR THE i, LINE CURRENT, PARTICULAR CARE BEING ace PAID TO HAVE LOW VOLTAGE DROP. S Se eal | = HANDLES THE VOICE SIGNAL, PERFORM- ntl ING THE 2/4 WIRES INTERFACE AND yy CHANGING THE GAIN ON BOTH SENDING AND RECEIVING AMPLIFIERS TO COMPEN- DiPts SATE FOR LINE ATTENUATION BY SENSING EITHER THE LINE CURRENT OR THE LINE ice VOLTAGE. IN ADDITION, THE LS656 CAN ree ‘ALSO WORK IN FIXED GAIN MODE Qa = ACTS AS LINEAR INTERFACE FOR MF, SUP- Sa act PLYING A STABILIZED VOLTAGE TO THE DIGITAL CHIP AND DELIVERING TO THE LINE SO20L THE MF TONES GENERATED BY THE M761 ORDERING NUMBERS : LS656AB (DIP16) DESCRIPTION LSe56AD1 (6020) The LS656 is a monolithic integrated circuit in 16- acteristics can be controlled by means of external lead plastic package to replace the hybrid circuit in components to meet different specifications. telephone set. It works with the same type of In addition to the speech operation, the LS656 acts transducers for both transmitter and receiver (typi- as an interface for the MF tone signal (particularly for cally dynamic capsules). Many of its electrical char-. M761 C/MOS frequency synthesizer). BLOCK DIAGRAM (DIP16) a we 6) <i) © “ {Jee AA te | 2 8 88 Coe — 9h tot ‘ian dono a yt 5 ose <i} <9 6 ; aa <| Lepe [-] & am ® O—O €° © 00 forrny June 1993 ne vunet9g3 2929237 OOSS4bO 938 MM — 111

[Symbol [Parameter Value | Unit | Line Voltage (3 ms pulse duration) [ae |_| Forward tine Gurent tm Reverse Line Current [= 150_ ma] Pi ___{ Total Power Dissipation at Tare = 70 °C - se __Teo _| Operating Temperature - a —45 to 70 Tsig, Tj__| Storage and Junction Temperature - = 65 to 150 THERMAL DATA ‘Symbol - Parameter _ | Value [Unit | R mjame_| Thermal Resistance Junction-ambient Max | 80 PIN CONNECTIONS (top view) DIP-16 SO-20L meowur ff sof) secneur une ? ssf} too Ic INPUT) 1 26 DMC tNPUT unio s sal) wrneur + Line 2 13 5 von urine fa 18 Be impor aus a0. fle sa) necenen oureur ains aor cla t7 Bamccerven eurrur sunt nes.orenss qs ie Paecetver ourpur acrcouson fie sa) wputetsecanes cats covract Ha 13 B= Line caw cover fe off sume oar TEST CIRCUITS no” won | 300 —_ =? ne ad }sr t | of yp ev + 3 “ 5 ; useses . 0 | Hesa | | i oms/ is g -" beg Ly a epee ye ane

ELECTRICAL CHARACTERISTICS (refer to the test circuits, Ve = 1 to 2V, IL = 12 to 80mA, St, S2 and S3 in (a), Tarb = ~ 25 to + 50°C, f = 200 to 3400H2, unless otherwise specified) CSmet[_Porier | ‘test onions [wn [on ax [Unt | SPEECH OPERATION vi | Line Voltage Tamp = 25°C vi | - i= 12mA 34 49 IL = 30mA 54 iL = 60mA 70 ‘Common Mode Rejection f= tkHz 50 | [we [a ] Sending Gain Tam = 25°C, f = 1kHz, | Via = 2mV | IL = 25mA 48 | 51 i= 50mA 44 47 Sending Gain Flatness Van = 2mV, fret = KHz +t (versus frequency) Sending Gain Flatness Vin = 3 mV, ha = 50mA, +t (versus current) $3 in (b) Sending Distortion f= 1kHz, l= 16mA le Veo = 75mV % | Vin = 900m % | |__| Sending Gain in MF Operation Vuw=2mv,s2in(o) [-30| | | «8 | 2 | Gr | Receiving gain Vai = 0.3V, f= 1kHz, Tan = 25°C i= 25mA -3 IL = 50mA -8 Receiving Gain Flatness (vs. current) | Vpi = 0.3V, ln = SOMA, + $3 in (0) Receiving Distortion fe ThkHz, k= 15mA Veo = 400m 3 Vho = 450mV i0 Receiving Ouptut Impedance Veo = 50mV (pins 12-13) Sidetone [f= 1kHz, Tene = 25°C, | st in @) Zu.__| Line Matching Impedance Va=02V,f=tkHz | 600 | 600 | 700] a | 3 | ie [re Cuenca Cons) [eee [= “ = 114

LECTRICAL CHARACTERISTICS (continued) MULTIFREQUENCY SYNTHESIZER INTERFACE Voo | MF Supply Voltage Stand by and | $2 in (b) 2a]2sle7| v | - foo Operation ag Ny ( | le a ESE Operation ma | - [wien Ye noo sf | wwe | x0. [a fronton enid—wenomwy pe] | m=) | [= [ose [wens son ismma [p= p= | + | Muting Threshold Voltage (pin3) | Speech Operation PT a fy f= ing age (Pi MF Operation 16} | vio Muting Stand by Current (pin 3) ) [=10| wa | - | |__| Muting Operating Current (pin 3) | $2 in (b) | +10] wa | - | CIRCUIT DESCRIPTION 1. DC Characteristic block diagram). The fig. 5 shows the DC equivalent circuit of the Fig. 6 shows a more detailed circuit configuration of LS656. the shunt regulator. A fixed amount lo of the total available current I is The difference I.-lo flows through the shunt regulator drained for the proper operation of the circuit. The being lp negligible. 1a is an internal constant current value of lp can be programmed extemallybychang- generator ; hence Vo = Vp + la. Ra=3.7 V. ing the value of the bias resistor connected to pin4 ~The Vi, I, characteristic of the device is therefore (see block diagram). similar to a pure resistance in series to a battery. The minimum value of lo is 7.5 mA. Itis important to note that the DC voltage at pin 5 is. The voltage Vo = 37 V of the shunt regulator is in- Proportional to the line current (Vs = V7 + Ve= (IL - dependent of the line current. |o) R3 + Ve). The shunt regulator (2) is controlled by a tempera- The DC characteristic of the LS856 is shown in ture compensated voltage reference (1) (see the fig. 7. Figure 5 : Equivalent DC Load to the Line. PING R pz tk , | -) ; - PINT Rp PINS aes 512 115

Figure 6 : Circuit Configuration of the Shunt Regulator. R2 6 RI 2 Le Ib |" | leo Ra ie Vo “| Rb | ta vb | WB 7 5 R3 cr saz ——O Figure 7 : DC Characteristic. . 4 o | taded EY f | J 2 . Haid A y FA anen on |_|

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  1. Two to Four Wires Conversion sensed across the second diagonal of the bridge The LS656 performs the twowires(line)tofourwires (pin 11 and 10). After amplification itis applied to the (microphone, earphone) conversion by means of a__receiving capsule. Wheatstone bridge configuration so obtaining the The impedance Zu is simulated by the shunt regu- proper “ooo between sending and receiving _ator thats also intended to work as a transconduc- signals (see fig. 8). tance amplifier for the transmission signal. . ine Ze Rt _ For a perfect balancing ofthe bridge 5° = 5 The impedance Zm is defined as aes The AC signal from the microphone is sent to one i ‘deri ‘rout diagonal ofthe bridge (pin 6 and 9). A small percent- Seal ny aration Wegerovatece Gireult for AC age of the signal power is lost on Zs (being Zs. ' ; >> Z) ; the main partis sent to the line via R1. in re- AV7 = AVA = AVe- — fe ceiving mode, the AC signal coming from the line is Ra+ Ro 116

The corresponding current is lois increased by means of the external resistor con- Avr nected to pin 4, the two above mentioned values of alsa the line current for the starting point and for the mini- 3 mum gain increase accordingly. Therefore , ina point wit Itis also possible to change the starting point without Zu = 58 2 a3 [1 + Be changing lo by connecting pin 8 to the centre of are- al Ro sistive divider placed between pin 5 and ground (the The total impedance across‘the ling connections __total resistance seen by pin 5 must be at least 100 (pin 11 and 9) is given by KQ). In this case, the AGC range increases too; for - example using a division 1 : 1 (50 K/50 K) the AGC. 2m. = Ri + Zui + Ze) starting point shifts to about |, = 40 mA, and the mini- : i mum gain is obtained at IL = 95 mA. In addition to By choosing 22 RY and Zp 2 Zw this operation mode, the Ve voltage can be main- Zu=Zu=R3 (1 +52 tained constant thus fixing the gain value (Rx, Tx) in- Ro dependently of the line conditions. The received signal amplitude across pin 11 and10 _-For this purpose the Vpp voltage, available for sup- can be changed using different value of Ri (of __ plying the MF generator, can be used. course the relationship Z\\/Zs = R1/R2 must be al-_b) When gains have to be related to the voltage at ways valid). the line terminals of the telephone set, it is neces- The received signal is related to R1 value according —_sary to obtain Ve from a resistive divider directly con- to the approximated relationship : nected to the end of the line. Va=2Vrice— This type of operation meets the requirements of the Ri+ Zu French standard. (See the application circuit of Note that by changing the value of R1, thetransmis- _fig. 13). sion signal current is not changed, being the micro- phone amplifier a transconductance amplifier. 4. Transducer Interfacing 3. Automatic Gain Control The microphone amplifier (3) has a differential input The LS656 automatically adjusts the gain of the Stage with high impedance (= 40kQ) so allowing a sending and receiving amplifiers to compensate for 90d matching to the microphone by means of ex- line attenuation, temal resistor without affecting the sending gain. ° : - The receiving output stage (6) is particularly in- This function is performed by the circuit of fig. 9. tended to drive dynamic capsules. (Low output im- The differential stage is progressively unbalanced —_pedance (100 max) ; high current capability 3 by changing Vo in the range 1 to 2 V (Vrera isan mAp). internal reference voltage, temperature compen- When a piezoceramic capsule is used, itis useful to sated). increase the receiving gain by increasing Rt value Itchanges the current Ia, and this currentis used as (see the relationship for Va). 2 control quantity for the variable gain stages (am- Writ very low impedance transducer, DC decou- pier (4) ang (6) in the block diagram). The voltage ying by an extemal capacitor must be provided to a oo a prevent a large DC current flow across the a) from the LS656 itself (both in variable andin fixed transducer itself due to the receiving output stage mode) and. offset. b) from a resistive divider, directly at the end of the | line. 5. Multifrequency Interfacing 1 a) Inthe first case, connecting Ve (pin 8) tothe regu- The LS656 acts asa linear interface for the Multifre- | lator bypass (pin 5) it is possible to obtain a gain quency synthesizer M761 according to a logical sig- i characteristic depending on the current. nal (mute function) present on pin 3. In fact (see fig. 6) When no key of the keyboard is pressed the mute Vs = Ve + V7= Ve = (IL~ lo) RB state is low and the LS656 feeds the M761 through The starting pointof the automaticlevel control isob- _pin 15 with low voltage and low current (standby op- tained at = 25 mA when the drain current __ eration of the M761). The oscillator of the M761 is lo=7.5mA. not operating. Minimum gain is reached for a line current of about When one key is pressed, the M761 sends a “high 50 mA for the same drain current lo=7.5MA.When _state” mute condition to the LS656. A voltage com- . 7929237 0059466 356 MM 117

APPLICATION INFORMATION

Figure 10 : Application Circuit with Multitrequency (Europe !! STD). | _ Ts nf gave FU peppy}. "os ends | fetsteler—fo ea seta (the et tae i LE: ond ™ od nd Bp a 2 43s Cas fe Fl (s 5 ~ | | Figure 11 : Application Circuit with Multifrequency (Europe | STD). n 5 3 | 16| oan 6 | M761 820pF 205 i [Jerkn. 7 7. A 209 [Joa | ‘# TOLLERANCE =22% { 19

Figure 16 ; External Mute Function. y 18 oo) iy 15 M761 Mute LS656B .S6568 Mute 5 3 3 Speech ‘Speect Ferre 5-528? a) with mulitifrequency b) without multitrequency In addition to the above mentioned applications, different values for the external components can be used in order to satisfy different requirements. The following table (refer to the application circuit of fig. 10) can help the designers. Component [Value | __ Purpose | Ne { Rt | 302 | Bridge Resistors | Ri controls the receiving gain. When high current values are Ro | allowed, R1 must be able to dissipate up to 1 W. ‘The Ratio R2/R1 fixes the amount of signal delivered to the line. R1 __ ___| helps in fixing the DC characteristics (see F3 note). PRS 302 | Line Curent | The relationships involving FS are: Se Fi bc Jf Gharaderste, | Zit. = (20 RAZ) + RI, Gs=K- AZM ang | Vi= (h, — lo) (RB + 4) + Vo ; Vp = 3.7V Without any problem itis possible to have a Zm. ranging from 600 up to 9000. As far as the power dissipation is concemed, see Rt note. i Ra 13kQ | Bias Resistor |The suggested value assures the minimum operating current. It is | possible to increase the supply current by decreasing Re (they are | | | inversely proportional), in order to achieve the shifting of the AGC _| _| starting point. (see fig. 16). After Rd changement, 30 RS __| 2.240 | Balance Network it's possible to change RS and RE values in order to improve the R6 6.8kQ. matching to different lines ; in any case : Pa = Re Zp = RS + RG/Xce R7-A7 | 1002 | Receiver R7 and R7’, must be equal ; the suggested value is good for ] Impedance Matching | matching to dynamic capsule ; there is no problem in increasing and | decreasing (down to 0) this value. A DC decoupling must be { inserted when low resistance levels are used to stop 8 | 2000 | Microphone { Impedance Matchin ct | 10uF Regulator AC ‘A value greater than 10 uF gives a system start time too high for | byPass tow current line during MF operation - a lower value gives an | alteration of the AG line impedance at low frequency. C2] 47nF | Matching toa C2 changes with the characteristics of the transmission fine. | apacitive Line Beoelving Gain C3 depends on balancing and line impedance versus frequency. latness ca 15nF | Balance Network | See note for R5, R6. __ - C5 0.33nF | DC Filtering ‘The C5 range is from 0.1 uF to 0.47 pF. The lowest value is ripple limited, the higher value is starting up time limited. c6-C7__ | 1000pF ca 100uF | Receiving Output | See note for R7, R7. DG Decoupling i} co 1 uF | Receiving Input DC | jane a BS7929237 0053947 713 122