LS656

LS656 STMICROELECTRONICS | Alldatasheet

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ee OeeEE—=——EeeeEeeeeeeeeeeee SG S-THOMSON O7E D Pf 7929237 ooLae2s a | : © eee es ee : : TELEPHONE SPEECH CIRCUIT WITH MULTIFREQUENCY : TONE GENERATOR INTERFACE The LS656 is a monolithic integrated circuit in sending and receiving amplifiers to compen- 16-lead plastic package to replace the hybrid sate for line attenuation by sensing either the : circuit in telephone set. It works with the same line current or the line voltage. In addition, type of transducers for both transmitter and the LS656 can also work in fixed gain mode. receiver (typically dynamic capsules). Many of __ it acts as linear interface for MF, supplying a its electrical characteristics can be controlled by Stabilized voltage to the digital chip end deli means of external components to meet different vering to the line the MF tones generated by specifications. the M761 In addition to the speech operation, the LS656 : acts as an interface for the MF tone signal (par- ticularly for M761 C/MOS froquency synthesizer), ao The L866 ssi functions ar the following: { oP DIP-16 Plastic — It presents the proper DC path for the line . (0.4) current, particular care being paid to have low rf voltage drop. — It handles the voice signal, performing the 2/4 ORDERING NUMBER: 1 S6568 wires interface and changing the gain on both BLOCK DIAGRAM — owt © ® @, hy ; + | a) 8 ¢6 2 7) Y YY poe | i Om Pls | Poor Tol eek i S16 oo ‘Tt ) : 8 © t QQ | 8 <h; 8 8 © o-O ® ® Yoo some 0497 a-02 361 6/86

; son a? aa off oS § G S-THONSON OVE D Bi vsese3? o01a . ; : Tek Foe tC 19397 T-15-07-165 i ee se . ABSOLUTE MAXIMUM RATINGS Ve Line voltage (3 ms pulse duration) 2 2 . Ie Forward line current 150 mA Ie Reverse line current -160 mA Prot Total power dissipation at Tama= 70°C 1 w Top Operating temperature -45to 70 °C Tag. Ty _ Storage and junction temperature -65to 150°C CONNECTION DIAGRAM (top view) MIC. INPUT {}* 16[]} Micineur ‘+UINE 2 151] Yoo MUTING 3 1e{] MF INPUT BIAS AO). fj« 13]] Receiver output snumtres. ffs raf] receiver oureut pcreouator [6 sf] inpute(REC.AMP) LINE CURRENT fy tof ineur-cnec.ame GAIN conTROL {]8 of] -tine THERMAL DATA Rin j-amp Thermal resistance junction-ambient max 80 °C/W a

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S G S-THOMSON OPE D | 7929237? OOLee? 1 i ee TEST CIRCUITS oA yon oa ce 1.8 re ee: 7 af go * are | ea ev —e a fm - } id oc ons . [FB A 69 2 FS} | Jit &, c4 {204 22pF 2apFet hal . ys p Fig. 1 Fig.2 ° Iz 12 to8OmA Ugiz toBOmA] G _- + ioaF] ear * - Test ‘) Re68KA au, =8.8K veo Jsooa ‘p[]soo L . 98 EE ter coe a Los O sist Side tone = “82 Gs= SO. V=01V cMR Ve Vu Fig. 3 Fig. 4 , S 1 ps2 to80ma Our Iswrosoma | & —l, oasy y* LOAF na [ Jeon Test Test cincutT dy circu GQ Sree] R=68KN. Or Reiko ‘wof ]e000] Ove ae LJ [aq] sagen ett . Yao Gue- YM Sr Vat Mr Vmr 363

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S G S-THOMSON O?E D I 7929¢e3? 00132248 3 | : . 5 chu SRE SSA 81C 19399 DB T-16-09-15 : ve} - ee e_—— ELECTRICAL. CHARACTERISTICS (Refer to the test circuits, Vg= 1 to 2V, I_= 12 to 80 mA, . $1, $2 and $3 in (a), Tamn= -25 to +50°C, f = 200 to 3400 Hz, unless otherwise specified). } a CC SPEECH OPERATION vi Line voltage Tamb* 28°C Ius12mA 3.9 . amp it=30mA a1 | ov IC= 60 mA 69 f=1 KHz [so [7 [fae a] G, Sending gain for B type | Tamp= 26°C f=iKHz I1=25mA | 48.5 505 Viz 2mV_ Ip=50mA | 445 46.5 G, Sending gain for AB T, = 25°C f=1KHz IL=25mA 61 * type Vane 2 mV I¢= 60 mA 47 ‘Sending gain flatness for | Vmi=2mV frog 1 KHz B type (vs. freq.) ‘Sending gain flatness for | Vi= 2 mV. from 1 KHz rz] AB type vs. freq.) {*)Sending gain flatness for | Vqi=2mV —__lyeg= 50MA 8 type (vs. current) sf io) . Sending gain flatness for | Viqi=2mV Wear BOMA AB type (vs. current) | S3in (b) Sending distortion for__| f= 1 KHz Vso" 775 mV B type Is 16 mA Vso" 900 mV Sending distortion for | f= 1. KHz Vso= 775 mV. AB type K=16mA Vso 900 mV [Sending noise for type | Vuj OV; Vez iv || = [69 [ame | 2 | a Ga type Microphone input Vee 2mV impedance {pin-16) Sending gain in MF Vaz 2mV operation ‘SZ in (b) Ga Receivinggain for8 | Va 0.3V 1L= 25 mA 55 35 type ron Tamb= 25°C 1,=50mA 10.5 85 Gp Receiving gain for AB | Vaj=0.3V 1L=25 mA 3 type f=1 KHz Tamp™ 25°C IL=50mA 8 . Receiving gain flatness | Vai 0.3V. From 1 KHz for B type (vs, freq.) Receiving gain flatness | Vqi= 0.3V from 1 KHz for AB type (vs, freq.) Receiving gain flatness Vat 0.3V Treat 50 MA 7 for B type (vs,current)_| Sdn (b) Receiving gain flatness | Vay=0.3V Tet 50 mA | fet yes] for AB type (vs. current) |_§3 in (b) Receiving distortion for | f= 1 KHz Vro= 400 mV B type IL= 15 mA Vpo@ 450 mV * Fixed gain mode. a 364

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ee ee=EeeeEeEEOOeEOOeeee S$ G S-THOMSON O?E D | 7929237? 0013229 5 I ‘ 81C 19400° D T-"5-01-\\8 PARAL oes i a a . . ELECTRICAL CHARACTERISTICS (continued) ee Od Receiving distortion for | f= 1 KHz Vro™ 400 mV AB type I= 15 mA VRo= 450 mV ca a type Receiving noise for AB. | Vai= OV; Va=1V WW type Receiving output Vro= 60 mV 30 impedance (pin 12-13) Sidetone fo 1 Ria |? | T, = 25° sfiriv) weer rer pe Pee impedance Tg Input current for gain HA control (pin 8) MULTIFREQUENCY SYNTHESIZER INTERFACE ° Vop MF supply voltage [ 25 | 27 | v . Stand by and Operation Too MF supply current ‘Stand by mA Operation mA - MF amplifier gain fae in= 1 KHz 7 VME in= 80 mV vi DC input voltage level vy = 80 mV vi v Ry Input impedance VF in= 80 mV. Ka (pin 14) d Distortion for B type | Vaar jq= 180 mVp 1 ma a Distortion for AB type | ViyF jn= 150 mVp. 4 ee ma [searing deta tine is tpingh [| ft ty [=] [MF opeatn tte | Tv [| Wuting dtand by current (bin 3) Mating operating +10 current (pin 3) os5o1 a-06 365 oad

SG S-THOMSON O7E D ff 7929237 0013230 1 &f , Co 19401 DT-1S-07-15 ee 4 ae 8 CIRCUIT DESCRIPTION : : 1. DC characteristic The fig. 5 shows the DC equivalent circuit of the LS656. Fig. 5 - Equivalent DC load to the line ~ PING R pin2 th oa Bis, A fixed amount I, of the total available current I. is drained for the proper operation of the circuit, The value of I, can be programmed externally by changing the value of the bias resistor connected to pin 4 (see block diagram). The minimum value of I, is 7.5 mA. - The voltage Vo= 37V of the shunt regulator is independent of the line current. The shunt regulator (2) is controlled by a temperature compensated voltage reference (1) (see the block diagram). Fig. 6 shows a more detailed circuit configuration of the shunt regulator. Fig. 6 - Circuit configuration of the shunt regulator R2 6 RI 2 un gy a Ib _ |! [!=s ra ve Yo Al . Re | la ve Ve ? s . a3 1 A ra : The difference 1,-I, flows through the shunt regulator being 1, negligible. 1, is an internal constant current generator; hence Vo= Vg +1, * Ra=3.7V. The Vi, Iy characteristic of the device is therefore similar to a pure resistance in series to a battery. a 366 0502 a-07 a

ee eeeeeEOEOEOEEeeeeeeE—EEEOEeeeeeee i ‘ s G S-THONSON O7E D ff 7929237 oo13231 3 i gic 19402, D T-D- 0115 passage ier i we v - : rw) oe ee i a It is important to note that the DC voltage at pin 5 is proportional Fig. 7 - DC characteristic to the line current (Vs= V7 + Ve= (IL-lo) R3 + Ve). spe ‘The DC characteristic of the LS656 is shown in fig. 7. “ H-eeeH-++HH-4 . He) A 4 EE i, | L471 [tT et o-Eee TTT Tre TT rrr »CeTr rT EEE Pri tits rr ar ar 2. Two to four wires conversion The LS656 performs the two wires (line) to four wires (microphone, earphone) conversion by means of a Wheatstone bridge configuration so obtaining the proper decoupling between sending and receiving signals (see fig. 8). Fig. 8 - Two to four wires conversion SEF cannione 7 QX n Yar A 2 vig | ize Ne . a worst shige > For aperfect balancing ofthe bridge, 2b = a The AC signal from the microphone is sent to one diagonal of the bridge (pin 6 and 9). A small per- centage of the signal power is lost on Zp (being Zp > Z:); the main part is sent to the line via R1. In receiving mode, the AC signal coming from the line is sensed across the second diagonal of the bridge (pin 11 and 10). After amplification it is applied to the receiving capsule. The impedance Zyy is simulated by the shunt regulator that is also intended to work as a transconduc- tance amplifier for the transmission signal, 367

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S$ G S-THOMSON O7E D Bi 2929237 oonze32 s oF Eee a 81 19403 D 1- 15-07-15 i y , SSEauEL:LC:U3G | pOUOMU yy SSS _ APPLICATION INFORMATION (continued) : ; The impedance Zyy is defined as AVe-9, Als-9 From fig. 6 considering C1 as a short circuit for AC signal, any variation AV, generates a variation: R . AV, = AVa = AVe* —_— 7 “ o* TR, +R The corresponding current change is AV, a= St Therefore AY, R Zm = —S-= ABV + =*) wR ‘ Rp The total impedance across the line connections (pin 11 and 9) is given by Zuc= R1 + Zm//(R2 +Zg) By choosing Zy > R1 and Z, > Zy Zr ¥Zm = R31 + 2) Re : The received signal amplitude across pin 11 and 10 can be changed using different values of R1 (of course the relationship Z_/Zg = R1/R2 must be always valid). The received signal is related to R1 value according to the approximated relationship: Ri Va=2Va = R BIRT +Zm Note that by changing the value of R1, the transmission signal current is not changed, being the micro- . phone amplifier a transconductance amplifier. 3. Automatic gain contro! The LS656 automatically adjusts the gain of the sending and receiving amplifiers to compensate for line attenuation. This function is performed by the circuit of fig. 9. Fig.9 7 ‘6 YREF o | 19 a

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s ¢ s-THortson ove. > Wf 2s29237 o013233 2 | > a Pa 7 The differential stage is progressively unbalanced by changing Vg in the range 1 to 2V (Vrere is an . internal reference voltage, temperature compensated). : It changes the current Ig, and this current is used as a control quantity for the variable gain stages i (amplifier (4) and (5) in the block diagram). The voltage Vq_can be taken: a) from the LS656 itself (both in variable and in fixed mode) and. b) from a resistive divider, directly at the end of the line. i a) In the first case, connecting Vq (pin 8) to the regulator bypass (pin 5) it is possible to obtain a gain 3 characteristic depending on the current. 2 In fact (see fig. 6) ; Vs = Va +V7 = Vp + (IL lo) RS : The starting point of the automatic level control is obtained at 1 = 25 mA when the drain current . 1, = 7.5 mA. Minimum gain is reached for a line current of about 50 mA for the same drain current | = 7.5 mA. : When Ig is increased by means of the external resistor connected to pin 4, the two above mentioned values of the line current for the starting point and for the minimum gain increase accordingly. - It is also possible to change the starting point without changing 1, by connecting pin 8 to the centre of a resistive divider placed between pin 5 and ground (the total resistance seen by pin 5 must be at least 100 Ka). In this case, the AGC range increases too; for example using a division 1:1 (60K/50K) the AGC starting point shifts to about 1, = 40 mA, and the minimum gain is obtained at I_ = 96 mA. In addition to this operation mode, the Vg voltage can be maintained constant thus fixing the gain values (Rx, Tx) independently of the line conditions. For this purpose the Vip Voltage, available for supplying the MF generator, can be used. b) When gains have to be related to the voltage at the line terminals of the telephone set, it is necessary to obtain Vg from a resistive divider directly connected to the end of the line. This type of operation meets the requirements of the French standard. (See the application circuit of fig. 13). ig. 13) . 4. Transducer interfacing . ‘The microphone amplifier (3) has a differential input stage with high impedance (= 40 Ka) so allowing ‘a good matching to the microphone by means of external resistor without affecting the sending gain. The receiving output stage (6) is particularly intended to drive dynamic capsules. (Low output impe- dance (1002 max); high current capability 3 mAp). - When a piezoceramic capsule is used, it is useful to increase the receiving gain by increasing R1 value (see the relationship for Vp). Whit very low impedance transducer, DC decoupling by an external capacitor must be provided to prevent a large DC current flow across the transducer itself due to the receiving output stage offset. 5. Multifrequency interfacing . The LS656 acts as a linear interface for the Multifrequency synthesizer M761 according to a logical signal (mute function) present on pin 3. When no key of the keyboard is pressed the mute state Is low and the LS656 feeds the M761 through pin 15 with low voltage and low current (standby operation of the M761). The oscillator of the M761 is not operating. eee 0505 a-10 369 Poa

sg satuonson_o7e » Ml asese37 ooxseas « M ; (he wee el B1C 19405 D T-15-01-\\5 i nee ~ When one key is pressed, the M761 sends a “high state” mute condition to the LS656. A voltage com- parator (8) of LS656 drives internal electronic switches; the voltage and the current delivered by the . voltage supply (9) are increased to allow the operation of the oscillator. This extra current is diverted by the receiving and sending section of the LS656 and during this oper- ation the receiving output stage is partially inhibited and the input stages of sending and receiving am- plifiers are switched OFF. A controlled amount of the signalling is allowed to reach the earphone to give a feedback to the sub- scriber; the MF amplifier (10) delivers the dial tones to the sending paths. The mute function can be used also when a temporary inhibition of the output signal is requested. . The application circuit shown in fig. 10 fulfils the EUROPE II standard (-6, -8 dBm). If the EUROPE | levels are required (-9, -11 dBm) an external divider must be used (see fig. 11).

APPLICATION INFORMATION

Fig. 10 - Application circuit with multifrequency (EUROPE II STD) oo + yon "9300 aro. a om grr te Fs] awe, to} —— sels’ etep ~uw Rs le] Tt wre | coun fs Ll rad | : sr [ae i i exaf] | yee 4 LE gF seer | Bary ig ake the tt? . 0 ew it en —— = ty Asa Fig. 11 - Application circuit with multifrequency (EUROPE | STD) Sa 5 : 16] ir INPUTS 14 wren | aor ie n| + + n09F []a 0506 ail 370 cad

ee — _ _ oo $ 6 s-THonson ove Ml 2929237 oo1az3s 0 —— : oS 81C 19406” D T-IS-09-15 5 ‘ prea ae ‘ oe so i ; A + ~ APPLICATION INFORMATION (continued) . . Fig. 12 - Sending and re- Fig.-13 - Application circuit without multifrequency : ceiving gain vs. line current 4 (application circuit of fig. 10) 2 oof LL | i see ae NE. > I aT “ EEEE SEH ‘ : Saye" Looe deel ase > rT Fig. 14 - Application circuit with gain controlled by line voltage (French standard) perteey une ~ pes iséess °f* = |S 4 ‘Tila a

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S SG S-THOMSON OVE D | 792923? 00139236 2 | : ’ c (oe 81C 19407 © DT- 15-07-15 we) : APPLICATION INFORMATION (continued) . Fig. 15 - Application circuit Fig. 16 - External mute function : with fixed gain operation LS656 Yoo! Py 18 hs % 8 ut Lses6 ? 49 5 M761 [Mute LS656 Mute 5 a ial ce Speea 2 . al i Tae y aim oan sont 4 iy ee aa a) with multifrequency b) without multifrequency + s-s150 y= 0 Main gain condition . Ry= 0 Main gain condition 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. Pee [we [ee R1 controls the receiving gain. When high cur- rent values are allowed, R1 must be able to , i dissipate up to 1W. Bridge Resistors The ratio R2/R1 fixes the amount of signal delivered to the line. R1 helps in fixing the DC characteristics (see F3 note), Line current sensing. The relationships involving R3 are: Fixing DC characteristic. — 2mc= (20 R3//Z_) + RI : Zu/IZpae Sse Kk R3 = Vim tl = lo) (RB + RI) + Voi Vo™ 3.7V. . Without any problem it is possible to have a Za ranging from 600 up to 9002. As far as the power dissipation is concerned, see Ri note. Bias Resistor The suggested value assures the minimum oper- ating current. It is possible to increase the supply current by decreasing R4 (they are inversely proportional), in order to achieve the shifting of the AGC starting point. (See fig. 16). After R4 changement, some variations could be found also in other parameters, i.e. line voltage. 372

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EEE EO OO —OV—Oee - $.¢ S-THonson ove » Mf 2929237 coxaea7 y {.- i ns 3 81C 19408 dD T-15-07- Oe. ned i vs ; j Balance Network It’s possible to change R5 and R6 values in order to improve the matching to different g lines; in any case: 7 2s _ R2_ Zz ORT Zp> RS+R6//Xcq . R7-R7" Receiver impedance R7 and R7; must be equal; the suggested value . matching is good for matching to dynamic capsule; there is no problem in increasing and decreasing {down to 02) this value. A DC decoupling must be inserted when low resistance levels are used to stop the current due to the receiver output offset voltage (max 200 mV), Microphone The suggested value is typical for a dynamic impedance matching microphone, but it is possible to choose R8 ina wide range. ct Regulator A value greater than 10 pF gives a system start ° AC bypass time too high for low current line during ME operation; a lower value gives an alteration of the AC line impedance at low frequency. c2 47 nF Matching to a C2 changes with the characteristics of the capacitive line transmission line. c3 Receiving gain C3 depends on balancing and line impedance flatness versus frequency. [ct | tS oF | ance network | See note for RB, RS, 0,33 pF The C5 range is from 0,1 uF to 0.47 uF. The . lowest value is ripple limited, the higher value : is starting up time limited, ce-c7 wo0opr | AFbyes TO cs Receiving output See note for R7, R7. DC decoupling . Receiving input DC decoupling 373

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