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unisonic technologies co., ltd l6726 linear integrated circuit www.unisonic.com.tw 1 of 13 copyright ? 2012 unisonic technologies co., ltd qw-r108-015,c universal speech circuit ? description the utc l6726 is a mask-programmable, monolithic integrated speech circuits for using in electronic telephones. it is designed for using with a low impedance microphone. transmitting and receiving gain are regulated with line length. different regulation for various current feeds can be set by external resistors. typica l current feeds as 48v 2200 ? , 48v, 2400 ? , and 36v, 2500 ? , can be handled. application dependent parameters such as line balance, side tone level, amplification and frequency response are set by external components. parameters are set independently which means easy adaptation for various market needs. the utc l6726 is developed for using with cmos-type dialer ics. a separate dtmf input is switched when the circuit is muted, and an adjustable dc s upply is provided for feeding an external cmos device. ? features *minimum number of inexpensive external components, 5 capacitors and 11 resistors. *mute function for operation with dtmf-generator. *transmit and receive gain regul ation for automatic loop loss compensation. *extended current and voltage range 5~130ma, down to 2v. *differential microphone input for good balance to ground. *balanced receiver output stage. *short start-up time. *stabilized dc-supply for low current cmos dialers and/or electret microphones. *dtmf-input controlled by mute. ? ordering information ordering number package packing lead free halogen free l6726l-d18-t L6726G-D18-T dip-18 tube l6726l-s18-r l6726g-s18-r sop-18 tape reel l6726l-s18-t l6726g-s18-t sop-18 tube
l6726 linear integrated circuit unisonic technologies co., ltd 2 of 13 www.unisonic.com.tw qw-r108-015, c ? pin configuration ? pin descriptions pin no. pin name description 1 +l output of the dc-regulator and trans mit amplifier. this pin is connec ted to the line through a polarity guard and diode bridge. 2 to output of the transmit amplif ier. this pin is connected through a resistor of 47 to 100 ? to -l, which sets the dc-resistance of the circuit. the output has a low ac output impedance and the signal is used to drive a side tone balancing network. 3 ti input of transmit amplifier. input impedance 17k ? 20% 4 +c the positive power supply terminal for most of the circuitry inside the utc l6726 (about 1ma current consumption).the +c-pin shall be connected to a decoupling capacitor of 47 f to 150 f 5 mute when low, speech circuit is muted and the dtmf input is enabled. maximum voltage (at mute) is 0.3v,current sink requirement of external driver is 50 a 6 gr control input for the gain regulation circuitry. 7 dcs the sense input to the dc-supply. 8 dco the output from the dc-supply. 9 dcc the control output from the dc-supply 10 di the input for the dtmf -signal. input impedance is 25k ? 20% 11 mo output of the microphon e amplifier or dtmf-amplifier 12 mi 1 input to the microphone amplif ier. input impedance 1.7k ? 20% 13 mi 2 14 -l the negative power terminal, connected to the line though a polarity guard diode bridge 15 ri input of receiver amplifier. input impedance is approximately 38k ? 20% 16 dr the control input for the receiver amplifier driving capability. 17 re 1 receiver amplifier outputs. out put impedance is approximately 3 ? . 18 re 2
l6726 linear integrated circuit unisonic technologies co., ltd 3 of 13 www.unisonic.com.tw qw-r108-015, c ? absolute maximum ratings parameter symbol ratings unit line voltage, t p =2s v l 0~22 v line current, continuous i l 0~130 ma operating temperature t opr -40~+70 c storage temperature t stg -55~+125 c note: absolute maximum ratings are those values beyond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functiona l device operation is not implied. ? electrical characteristics (t a =25 unless otherwise specified) parameter fig. test conditions min typ max unit line voltage 1 i l =15ma 3.3 3.7 4.1 v i l =100ma 11 13 15 transmitting gain, note 1 1 2010log(v 2 /v 3 ), 1khz r l =0 ? 41 43 45 db r l =400 ? 43.5 45.5 47.5 r l =900 ? ~2.2k ? 46 48 50 transmitting range of regulation 1 1khz, r l =0 ~ 900 ? 3 5 7 db transmitting frequency response 1 200hz ~ 3.4khz -1 1 db receiving gain, note 1 1 2010log (v 4 /v 1 ), 1khz r l =0 ? -18.5 -16.5 -14.5 db r l =400 ? -16 -14 -12 r l =900 ? ~2.2k ? -13.5 -11.5 -9.5 receiving range of regulation 1 1khz, r l =0 ~ 900 ? 3 5 7 db receiving frequency response 1 200hz ~ 3.4khz -1 1 db microphone input impedance pin12,13 1 1khz, note 3 1.7(//2.7) k ? transmitter input impedance pin 3 1 1khz 17 k ? transmitter dynamic output 1 200hz~3.4khz, 2% distortion, i l =20~100ma 1.5 vp transmitter max output 1 200 hz~3.4khz, i l =0-100ma,v 3 =0.1v 3 vp receiver output impedance 1 1khz, note 3 3(+310) ? receiver dynamic output ( note 2 ) 1 200hz~3.4khz 2% distortion, i l =20~100ma 0.5 vp receiver max output 2 measured with line rectifier 200 hz~3.4khz, i l =0~100ma, v 1 =0~50v 0.9 vp transmitter output noise 1 p sof -weighting, rel1 v rms , r l =0 -75 db psof receiver output noise 1 a-weighting, rel 1v rms , with cable 0~5km, =0.5mm, 0~3km, =0.3mm -85 dba mute input voltage at mute (active low) 1 0.3 v d c -supply voltage 1 i l =10~100ma, i dc =0ma 2.35 v i l =10~100ma, i dc =2ma 2.2 dc-supply current, pin8 1 2 ma dc-output pin8 input leakage current (no supply) 3 v dc =2.35v 0.1 a dtmf transmitting gain 1 v m =0.3v 24.5 26.5 28.5 db notes: 1. adjustable to both higher and lower values with external components. 2. the dynamic output can be double d, see applications information. 3. external resistor in the test set up.
l6726 linear integrated circuit unisonic technologies co., ltd 4 of 13 www.unisonic.com.tw qw-r108-015, c ? functional diagram 10 12 13 dc 7 9 851132 15 16 6 14 4 17 18 ar at am 1 utc l6726 1.impedance to line and radio interference suppression. 2.transmit gain and frequency response network. 3.receive gain and frequency response network. 4.side tone balance network. 5.dc-supply components. ad dtmf input dc output for external cmos device 5 2 4 1 3 mute (active low) telephone line +line -line rec mute v m v4 i l dtmf i dc v dc artificaial line c1 1 f 600 v1 v2 r load =400 +400 v l fig. 1 test setup without rectifier bridge 5h+5h r l =0~4k 0 when artificail line is used c1= 1 f when artificial line is used 470 f when not used v3 mic z mic =350 z rec =350 e=48.5v utc 6726 with external component see fig 3 + + +line -line rec mute v m v4 i l dtmf i dc v dc c1 1 f 600 v1 v2 v l fig. 2 test setup with rectifier bridge 5h+5h r l =0~4k e=50v uz=(15 ~16)v mic v3 z mic =350 z rec =350 r load =400 +400 utc 6726 with external component see fig 3 + +
l6726 linear integrated circuit unisonic technologies co., ltd 5 of 13 www.unisonic.com.tw qw-r108-015, c ? functional diagram(cont.) c8 220nf 10 12 13 dc 7 9 8 c7 47 f r5 22k 5113 2 c3 100nf r6 75 r9 11k r8 r7 910 c4 47nf r11 c5 r13 11k r15 10 15 14 6 14 4 r1 r2 47 f 910 r3 c2 15nf r14 310 r10 * * 1 7 1 8 ar at am 1 utc 6726 +line -line dtmf input mic 350 dc supply out cmos device sense input control output ad r4 18k 560 3k mute 100nf note : * not used in test setup fig. 3 circuit with external components for test setup. 82k rec 350 c1 + + r16 27k
l6726 linear integrated circuit unisonic technologies co., ltd 6 of 13 www.unisonic.com.tw qw-r108-015, c ? functional description the gain of the transmitting and receiving amplifiers are continuously and euqually changed with the line length. the starting point for the gain regulation is externally se t .the gain regulation can be cut-off externally, see table under gain regulation below. the outputs of the transmitting and receiv ing amplifiers have internals limit ations of the output amplitudes. the circuit includes a temperature independent voltage re ference used for regulation of the dc line voltage and for the transmitting and receiving gain regulation. the dc voltage is very fast settled to its final value with a minimum of overshoot. the circuit uses a minimum of external components. in a normal practical case only 5 external capacitors of which only one is an electrolytic/tantalum f ilter capacitor .the other capacitor are needed as radio interference suppression capacitor over the line, one capacitor in the side-tone balancing network and one capacitor for low frequency cut-off in each of the transmitting and receiving amplifiers. the freque ncy response is except for that, flat for both amplifiers. the circuit will with external components get a very good return loss behavior both against purely resistive lines as for instance 600 ? and against complex networks as 900 ? in parallel with 30nf. to get a good cmrr the microphone input is balanced. it is possible to add a push-button controlled cut-off of the transmitting amplifier to the circuit without any disturbance of the ot her circuit functions a mute input is included in the circuit. it gives: 1. cut-off the microphone amplifier. 2. reduced gain in the receiving amplifier. 3. connection of the dtmf input. the receiver amplifier is equipped with a high impedance input stage. this gives a less expensive rc-network on the input. only resistive elements are used to set the receiving gain. a push-pull power stage in the receivin g amplifier gives a high output swing. to get the extended low current and voltage range two resistors have to be connected from microphone input to ground. the side-tone balanced can be set by a rc-network wit hout influence on other par ameters. an inexpensive solution requires only one capacitor while more capacitors can give better performance. in fig.4 ?? and are rc-links with the following functions: 1. for radio interference suppression and to give the correct return loss behavior. 2. to set the gain and frequency response for transmitting. 3. to set the gain and frequency response for receiving. 4. to set the side-tone level a stabilized dc output, with a pre-set outpu t voltage of 2.35v, is provided to fac ilitate interfacing to external coms dialer ics. the voltage is adjustable wi th two resistors, as indicated in fig. 5. the output requires some filtering to avoid distortion on the telephone line. no te that a high current cons umption of the external device will alters the dc characteristics of the speech circuit.
l6726 linear integrated circuit unisonic technologies co., ltd 7 of 13 www.unisonic.com.tw qw-r108-015, c ? functional description(cont.) + - 1.2v 15k 15k r dc1 r dc2 + 0~470 14 7 9 8 + 4.7~47 f 0~470 v dc1 v dc2 +line 1 fig. 5 dc regulator for external cmos devices
l6726 linear integrated circuit unisonic technologies co., ltd 8 of 13 www.unisonic.com.tw qw-r108-015, c ? application information refer to fig. 6 gain regulation (r1, r2): these resistors set the starting point for the gain-and side tone regulation. input impedance pin 6 is about 5.5 k ? 20%. below are some typical values for r1 and r2, for some different supplies from telephone stations. battery feed r1 r2 r6 no regulation set for short line gain. all feedings 22k ? 47~100 ? regulation: 48v, 2200 ? 48v, 2400 ? 36v, 2500 ? 180k ? 47 ? 75 ? 100 ? impedance to line (r3, c1, c2): c1 in series with r3 and those in parallel with c2 give the impedance to the line from the set. c2 must normally be there for the interference too. the network is optimized with regard to the return loss. the time constant r3, c1 cannot be allowed to be too sma ll. if the time constant is to small, distortion at low frequencies may be generated. if r3 is changed this will change the dc-c haracteristic too, which set by the volt age at pin 4. the i nput current at pin 4 is about 1ma microphone selection (m1, r16): the microphone can be either dynamic, magnetic or electrets. see fig. 12, 14 and 15. the input impedance between pin 12 and 13 is about 1.7k ? with typical variation 20% transmitting gain and frequency response (r4, r5, c3, c4): the network gives the amplification and frequency resp onse for the transmitter. r5 is used when a greater reduction of the gain is wanted. input impedance at pin 3 is about 17 k ? with typical variation 20%.the sum of the resistors r4 and r5 must not be less than 35 k ? because of dc-current to ground. below is some simple variations of this network. (see fig. 7). dc-characteristics (r6): sets the dc-characteristic and take care of some of t he supplied power. the resistor have also function with the protection of the circuit, the transmitter, the gain regulation and side tone. common values are 47 ? to 100 ? . side tone level, receiving gain and frequency response.(r7,r8,r9,r10,r11,c5): the network sets the side tone balance. the network in the application is one of many possibilities. r10 and r11 balance together the signals that go two different ways fr om the transmitter output stage o ne from pin1 and the other from pin2. the balance network consist of r8, r9 and c5. the example is not optimized to any specified line, it is only given to show the principle. fig8, 9 and 10 are examples of balance networks. fig.10 is especially suited for lines with high current supply. r12, r13, c6, (r10, r11): the networks gives the gain and frequency response for the receiver. input impedance at pin 15 is about 38 k ? with a typical variation of 20%.for different possibilities for the design of the network, see the network for the transmitter (r4, r5, c3) rec, r14: r14 generates the output impedance to the magnetic earphone (fig.11). if a dynamic earphone is used it should be placed between pin 17 and 18.see fig. 16.
l6726 linear integrated circuit unisonic technologies co., ltd 9 of 13 www.unisonic.com.tw qw-r108-015, c ? application information(cont.) r15: this resistor is used to set the driving capability of the receiver output amp lifier. common values are 0 ? to 50 ? . setting it for low driving capability results in function at lower line current. breaking up pin 16 will give lower power consumption and total mute of the receiver when muting the circuit. disconnecting pin 15 will of cause also give total receiver mute. d1, d2, d3, d4, d5: rectifier bridge and over voltage prot ector. the zener voltage at d5 should be as low as possible. common values are between 12v~16v. r dc1 , r dc2 : refer to fig. 5 the pre-set output voltage of 2.35v can easily, if needed, be changed to another value by applying one or two resistor(r dc1 ,r dc2 ) in parallel with the internal resistors (each 15k ? +/-20%).it is possible to get a rather high voltage and current from the dc-supply as long as the high current and voltage is available fr om the line. the dc voltage has to be filtered by a capacitor and this can, at high dc-voltage and low line cu rrent, interfere with the signal on the line and cause distortion. you can minimize the interference, with a resistor in series with the filter capacitor. the dc voltage will, of course, be more dependent of the dc-supp ly current. the dc-output pin has a very low input leak current, to allow stand-by feeding of the dialer. it is al so possible to use pin 9 to f eed microphones etc. that do not need stand-by feeding, without interferi ng with the stand-by feeding on pin 8. no te that a high current consumption by the external device will alter the dc characteristics of the speech circuit
l6726 linear integrated circuit unisonic technologies co., ltd 10 of 13 www.unisonic.com.tw qw-r108-015, c ? application information(cont.) ad am 1 2 3 4 56 7 89 * 0 # 220nf 47 f dc 7 89 13 12 10 51132 at 1 100nf 75 22k 560 100 nf 11k 10 15 16 6 14 4 * * 910 47 f 15nf 17 18 ar utc l6726 10 fig. 6 typical tong dialling telephone dtmf output dc mute out gnd sense input 11k 6.2k keypad dtmf dialler (cmos type) note : * not used in test setup 82k 910 18k telephone line u z =12v control output
l6726 linear integrated circuit unisonic technologies co., ltd 11 of 13 www.unisonic.com.tw qw-r108-015, c ? application information(cont.) design procedure: 1. circuit impedance to the line. 2. dc-characteristic 3. gain regulation. 4. transmitter gain and frequency response. 5. receiver gain and frequency response. 6. side-tone. 7. components to suppress radio interferenc e, specially the wires up to the handset. others: the circuit can be placed either in the telephone or in the handset. cut off the transmitter can be done at f1 without in terference of other functions of the circuit. when using the extended low current and low voltage range (5 ma, 2v), two resistors have to be connected from the microphone inputs to ground as shown in fig. 13. 11 3 r a c a 11 3 r a c a r b c b fig. 7 examples of network "2" r a 2 15 r10 r11 +line r b r 6 fig. 8 examples of network "4" r a 11 3 11 3 c a r a c a c a r b r b c b r b r a c a 11 3 11 3 r b c b r a c a r a r b 11 3 11 3 c a c a r a c b r b c b 2 15 r a r b r 11 c b r c r 6 c a +line r10 2 r a r 11 15 r10 +line r b r c r 6 c a
l6726 linear integrated circuit unisonic technologies co., ltd 12 of 13 www.unisonic.com.tw qw-r108-015, c ? application information(cont.) fig. 9 typical sidetone network fig. 10 sidetone network especially suited for applicatons with a high line current,when r6 has a low value +line r10 r12 c6 15 2 r11 ra rb r6 rc low impedance network. +line zbal c6 15 c r6 2 * to get flat response for receiving r12 fig.11 magnetic reciever connection r14 17 18 200 200 1 f 1 f 12 13 14 4 fig. 12 electret microphone with fet buffer am 12 13 50k 50k mic fig. 13 additional components for extended low current/voltage oeration 13 12 fig. 14 connection of a magnetic microphone 11 -line
l6726 linear integrated circuit unisonic technologies co., ltd 13 of 13 www.unisonic.com.tw qw-r108-015, c 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.

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