PBL3726/8 | DigiCamel IC Datasheet

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PBL3726 STMICROELECTRONICS | Alldatasheet

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7 SGS-THOMSON PBL3726

MASK - PROGRAMMABLE SPEECH CIRCUITS ADVANCE DATA Key Options External Components (step by step) « MICROPHONE TYPES SUCH AS ELECTRO- —_» DC CHARACTERISTICS DYNAMIC/MAGNETIC, ELECTRET OR CERA- —g IMPEDANCE MIC « TRANSMIT GAIN * POWER SUPPLY FOR EXTERNAL CIRCUL 4 TRANSMIT LINEARITY = RECEIVE GAIN = AGC CIRCUIT = RECEIVE LINEARITY

1 LINE REGULATION OF TRANSMIT/RECEIVE SIDETONE

GAIN FOR CERTAIN TELEPHONE STATION © POWER SUPPLIES = LOW VOLTAGE OPERATION = EXTRA POWER SUPPLY INPUTS FOR OUT- | PUT AMPLIFIER TO BE USED INHAND-FREE © DESCRIPTION TELEPHONES PBL3726 is a family of mask-programmable speech A SPECIAL IMPEDANCE/GAIN REQUIRE- _ <icuits intended for various telephone applications. "MENTS The flexibility of these circuits allows use of versions | MUTE OR TRANSMIT/RECEIVE AMPLIFIERS 0 PBL3726 in all telecom markets, whether it be in : WITH OR WITHOUT CONFIRMATION TONE _ ordinary telephone, a hands-free multi-function « ACOUSTIC SHOCK ARRESTORS phone or even as a trunk interface. The versatility is based on three levels :

1 SIDETONE CANCELLATION CIRCUITRY ased on three fevels

= Mask options for special requirements Pin Options = Pin options on certain functions = Step-by-step design possibilty on the basic = MUTE/NO MUTE FUNCTION telephone functions making it possible to cut = REGULATION OF SIDETONE WITH LINE down design time to a minimum. This is done LENGTH by changing the values of a small number of = CUT OFF OF ALL LINE REGULATION external components. ABSOLUTE MAXIMUM RATINGS Maximum Ratings over Operating Free-air Temperature Range (unless otherwise stated) [Symbol[ Parameter | Test Conditions | unit | [Voc [tineVotagetp=2s | [loc | Continuous Operating Line Current) | tm [| vuretion Temperature Te tO (7) Max current increases nearly upto 130mA with max operating temperature lowered o + 56°C November 1988 1736 | ‘si aarcod elon on anew enon W eaopRAT Oa oaaN DAS we RENEW TER

Figure 1 : Block Diagram and Typical Application. i | ' i Jor H ‘ o o i—+4 ' i PEL 3726 ? aon rt i : ‘Ol Dp > => [> ii +s: wwe =| L : | oO —o-0 © 6i4 11 a se oo os External RC-networks 4) Line impedance and radio interterence suppression 3) Receiver ampifir, gain set and frequency acjustment 2) Transmiting ampitier, gain set and requency adjustment 4) Side tone adjustment For recommended operating conditions see specific data sheets for different versions of PBL3726 FUNCTIONAL DESCRIPTION The gains of the transmitting and receiving ampli-__The circuit has an excellent return loss characteris- fiers are continuously and equally changed with the __tic against both purely resistive lines such as 600 2 line length. The gain regulation can be cut off exter-___and against complex networks such as 900 in par- nally, and the gain will then be the maximum gain _ allel with 30 nF. normally used at long lines. ‘The microphone input is balanced to provide a good The outputs of the transmitting and receiving ampli- = CMRR. fiers have internal limitations as to the output ampii--_ tig possible to add a push-button controlled cut-off tudes. of the transmitting amplifier of the circuit without dis- The circuit includes a temperature independent volt- _turbing any of the other circuit functions. age reference used for regulating the DC line cur- A mute inputs included to : rent and for regulating the transmitting and receiving 4) Cut off the transmitting amplifier (F:) gain. The DC voltage quickly settles toits final value >) Requce gain in the receiving amplifier with a minimum of overshoot. 3) Reduce current consumption to lower power loss The circuit needs few external components. Inanor- mal practical case there are only 5 external capaci- ‘The DC regulation works independently of the mute tors, one of which is an electrolytic/tantalum filter function and is not influenced by the mute signal. capacitor. The other capacitors are neededfor radio External mute-control of the circuit from a DTMF interference suppression, to function in the sidetone generator is then possible. balancing network, and to provide low frequency _The receiver amplifier is equipped with a high im- cut-off in each of the transmitting and receiving am- —_ pedance input stage, allowing a less expensive RC pifiers. network on the input. . B86 ee scs-tuomson | SYM vucroa scracmce 244

Rt, R2. The network is optimized with regard to the return These resistors set the starting pointforthegainand SS sidetone regulation, The R3, C1 combination forms a low-pass filter in Input impedance on the regulator is about 52KQ+ _the DC-feedback loop of the transmitting amplifier. 2%. Only universal versions of PBL 3726 like 1 the R3 Ct time constant is too low there may be PBL3726/6, 3726/9 etc. are equipped with this op- _distortion at low frequencies. tion. In the data sheets for these versions there isa__if R3 is changed this will change the DC characte- table showing the Rt, R2 values for different central istics too which is set by the voltage at Vop. The office power supplies. The regulation can also be input current at Voo is about 1mA. cut off by leaving Rt open and shorting R2 to-LINE voltage. R4, R5, C3, C4. For other PBL 3726 versions the regulations setin- The network gives the amplification and frequency ternally for a specific power supply type. response for the transmitter. RS is used when a greater reduction of the gain is wanted. Input imped- C1, C2, R3. ance at F2 is about 17KQ with typical variation C1 in series with R3 and these in parallel with C2 + 20%. The DC load on F; must be greater than determine the impedance to the line from the set. 40K, C2 is normally inserted for radio interference sup- pression. Figure 4 : The PBL3726 and External RC Networks. se nT.) H H | i mf] 1 H Hi res re o> H iy. O15" ) or) fe > zat be ee taal i i alan ees rs i jo} f ° grag ide | H ' 1® 4/36 . | SS 246

Figure 5 : Typical Filters, Fy Fa Fy Fo Ra Ra a Re | |e Ra ° is Fy F2 6, 9 = Ra a Ca 7 = i) Re Cy fF Fo non a ce Ra Ca Re Fy F2 Fy F2 te c Ry A. Ca ms Re CB ; S$-8534 536 G7 Seoneitones re

Re. R10 an R11 together balance the signals that exit Sets the DC Characteristics and dissipates some of _ two diferent ways from the pransmitier output stage, the supplied power. The resistor also affects, the 0N@ from pin 1 and the other from pin 2. The bal- transmitter gain, the output amplitude from the @Nce network consists of R8, R9 and C5. transmitter, the gain regulation and the sidetone. Examples given in the data sheets for different ver- Common values are 682 to 822. sions of PBL3726 are not optimized to any specified Figure 6 : Typical DC Characteristics. line : they are given only to show the principle. sam Amplifier F3 has a high input impedance. oT TT TTT] Shown in fig. 7 are some different sidetone net- Li ty Py works, wE ETT TT TTT] Construction of a sidetone network with regulation eT T wirree 5 according to the above can be done as follows : et. | TTT ee The balance impedance A is optimized at a short Ene cane line where the regulation starts. The balance imped- aan caneee ance Bis optimized at a long line where the regula- ‘ HAS tion stops. The circuit generates a continuous qa 4eeeeee change between the two balance impedances. Rx ATI insures that no DC voltage shall be between Fs's CriTPrer tT double positive inputs at the change. ° wm may By breaking up between the negative input and out- . put of Fs it can be used as an amplifier with amplifi- R7, R8, RY, R10, R11, C5. cation greater than unit. In fig. 8 two balance This network sets the sidetone balance. The net- networks without F3 are shown. Fs can then be used work in the application is one of many possibilities. __in other applications. Figure 7 : Sidetone Network. f a ‘TYPE :UNREGULATED "2 a TYPE: REGULATED cS ee cor aa i ae [Rc ety [Jne i [i ! ere % . fe fy Yoo Fr Fh yype unnecuateo

9 O+ 9 fe oF TYPE: REGULATED Ra Os O+

os Pad BS tg ok ee [Ja aoe eae aa ° (re: ij ea [re hook i a oe ea SoBe. PE wCoATED Re t&. 6196 248

In fig. 9 a circuit is shown, where Fs is used as an Figure 8 : Sidetone Netrwork without F3. amplifier with an extra 20dB gain at receiving and with a volume control. LINE R12, R13, C6 (R10, R11). The network gives the gain and frequency response Pe og for the receiver. Riz R13 is used when a greater reduction of the gain is os wanted. Input impedance Fs is about 35KQ with ty- 2 an pical variation + 20%. For different possibilities for 9° transmitter (R4, R5, C3) in fig. 5. i i i R14. ' | Generates the output impedance to the magnetic ' ! earphone. Rei} ' if a dynamic earphone is used it should be placed | 1S MADE LOW OHMIC between outer connections, The middle connection p ' is then not used. Led This will give about a double output (for the same output current). Rectifier. Rectifier bridge and over-voltage protec- vune tor. The zener voltage at fig. 10 should be as low as possible. Common values are between 12V and 16V. copes : H : i i i ‘ 2yail ‘ '

2 H/o

high receive gain attenuation is needed. The fre. The subjective effect of this is best seen in the for- quency response can be altered with the same fitters mula above for "Side Tone Masking Rating’. used for the send gain (see fig. §). To get protection summed at the frequencies f = 0.2, against acoustic shock the diodes provided on some " ‘One or two diode pairs can be used. Should this not Ws = Weighing factor be enough a resistor can be connected after the Le = Leakage at receiver capsule diodes (in series). This should be done before the S< . Send sensitivity setting of the receive gain. : . Sa = Receive sensitivity Figure 21 : Typical Receive Gain. Ast = Hybrid-loss balance The par that can be alteren by the speech circuit is i eoxn the Arst value that can be determined by the formu: KA gern la: +E Zc +Zso Z+Z . 2zZ0 Z-Zs0 P| Where : PBL 3726 Z = Impedance of the connected telephone line - Zso = The balance impedance of the central office > (PABX) ~ ; Zc = Impedance of the speech circuit i The sum of Z and Zso can be called Zine j The principle of the traditional so called active i speech circuit has been the wheatstone bridge (fig. i Sener 23). The formula for the minimum sidetone is to ba- lance until : : ae 2 2oa ISS SNSSSSSSSS Fe of | A | gure 22: corr actos. nso 4 a SSSASASWN SSSN We ° " ton | [oa en 07 | [ os |e 2 SIDETONE [oes [ere | 26 | 10 m [oe | saa | 32 | STMR=-—x 1009 (18 — (Wert le Ss+Sn+Aw} [1 | 497. ~«(| 23 —=«| . = 1010 | 25 | eo 2 i= eS et | The most difficult part of the design workisaways [2 | so7 | 36 =| | t0.define the sidetone. This should always be done [35] asa | 7a | last when designing with PBL3726, The sidetone is. "the sound of your own voice fed back into the ear by the handset. ee 4 11/36 | Gy ses.Twomson, 8 253

The principle of PBL3726 is more complicated(even _ Figure 23 : Balance Bridge. if calculation with the bridge in fig. 23 is possible). With the all-active bridge a method of cancelling the — sidetone is a summing amplifier makes it possible 2 | to get not only one but two different sidetone opti- | mums for different line lengths (see fig. 25). The function of the external components in fig. 7 have Vine 22 previously been described in this document. Fig. 26 i shows an example of a sidetone network using the Zoat || Wheatstone principle with PBL3726. Seon Figure 24 : Unregulated Sidetone Network. (] Moen er PELE i bel Ka [Jeena ow tH LEVEL oe y. if YY I) APOC CALE ADORE CACO, s-ss0 i ! ae oe TK0

1296 Ky Scs:THOMSON

Figure 25 : Regulated Sidetone Network. fom + [|e 2200, ea{] | veven see = LIne LENGTH ETE, 255

Product Information

PBL3726/8 specifications and overview.

Summary

MASK - PROGRAMMABLE SPEECH CIRCUITS

Description

MASK - PROGRAMMABLE SPEECH CIRCUITS

Source title PBL3726/8 Datasheet(PDF) - STMicroelectronics

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