DE3223607A1 - Hybrid transistor circuit for telephone sets - Google Patents

Abstract

A hybrid transistor circuit for telephone sets is provided whose whole equivalent electrical circuit for alternating current consists of three transistor circuits, comprising an output amplifier, a balancing amplifier and, finally, a separate transistor.

Description

PETROVIO Marko
Jevremova 25
YU-llooo Beograd

TRANSISTOR FORK FOLDING FOR TELEPHONE SETS

The transistor fork circuit according to the invention solves the problem the back loss without differential transformer. She is predominant intended for the electroacoustic part of the telephone set, but it can also be used for other simultaneous arrangements Pick-up / delivery can be used via a double-wire line.

So far, many such circuits have been invented (see for example the German revelations 1487228, 1762o58, 1762249, 18157o7, 19ol337, 2246o22, 2259993, 27571oo).

In comparison with such already known circuit arrangements, the transistor fork circuit according to the invention has advantages, (which are listed below) - namely:

- the back loss, adjustment of the line impedance and gain are solved in a simple way, through a basic circuit that has only three transistors.

- All transistor circuits have a strong negative reverse voltage on .why their work is practically not dependent on the characteristics of the transistor.

- The direct current circuit can easily be carried out in such a way that the circuit is carried out with direct current from the telephone line the DC voltage at the ends of the line can be small (which in the case of long telephone lines to the Comes out).

- 2-

In the following text, the invention is based on the enclosed three Drawings, where:

Fig. 1 is an equivalent scheme for alternating currents of the invention Represents transistor fork circuit; Fig. 2 shows a variant embodiment of the arrangement that the Scheme from Fig. 1 is equivalent. The supply from the sources of the stable direct currents was used, which is only hinted at

Fig. 3 shows an electroacoustic part of a telephone set represents, in which the circle of FIG. 2 was used, from the telephone line over power sources, which are shown in detail are fed.

The explanation of the mode of operation of the circuit according to the invention let's start with FIG.

L ₁ and L ₉ are ends of the telephone lines. Z _T is the impedance of the telephone line for alternating currents.

H is generally the recipient. In the case of a telephone

apparatus is the hearing aid group.

Z is the input impedance of the receiver.

M is generally the sender. In the case of telephones, this is the microphone circuit.

The equivalent circle according to FIG. 1 can be divided into the following three circles will:

- Amplifier, let's call it an output amplifier, with the transistor T ₁ , which has the impedance line Z _T in the collector circuit and the one in the

Emitter circuit is the impedance Z ₉ .

- Amplifier, let's call it a balance amplifier, with the transistor T ₀ , to which the Z., the collector impedance, and Z_, the emitter

impedance is, and

- the circuit of the transistor T_, which on the line with the emitter is the impedance Z and in the collector circuit is the receiver H, or its input impedance is Z ".

It will be seen later that this third circle is the emitter signal from the received signal and separates the input impedance

the entire circuit arrangement of the impedance line Z_ adapts.

All three transistor circuits listed have emitter impedances, which have such a strong negative feedback that their operation is practically independent of the characteristics of the transistor is.

From the emitter (or microphone circuit) M, the same signal is fed _{to the bases of the transistors T 1 and T ″.} The bases do not have to be galvanically connected. It is only important that the same voltage, which we will denote by U, is applied to both bases.

First we will consider the emission in the situation when there is no reception signal from the line.

It is evident that if the alternating voltages on the collectors of the transistors T ₁ and T ~ are the same, that is, if the difference in alternating voltage between them is equal to zero, then the circuit of the transistor T- is not conductive for the Alternating current. Therefore, no voltage appears at the input of the receiver H which is _{excited by the voltage U from which the base of the transistor T and T 0} is. In other words, there is no back-listening. In addition, the alternating current circuit of the transistor T ₁ (with its emitter impedance Z, - and its collector impedance Z "7) can be mentally removed without changing anything in the remaining circuits for alternating current of the output r and the balancing amplifier, s, derive the ratios of their impedances, give the same alternating voltages to the collectors of the corresponding transistors T and T ".

The alternating voltage on the collector of transistor T ₁ is the

- u _M

^Z 2
very approximate.

This voltage is the sender signal that the output amplifier sends sends to the telephone line.

3223ÖU7

The alternating voltage is on the collector of the transistor T_

4 ·

^Z 3
By balancing the stresses listed, you get

Z ₄ -Z ₁ . (1)

.4 = L

^Z 3 ^Z 2

which is a condition "which the impedances have to meet in order to to fight backhearing completely.

The left hand side of the above equation is voltage gain of the balancing amplifier , and the right hand side is the voltage gain of the output amplifier.

Now, when the above condition i1) is fulfilled, we shall mentally return the circuit of the transistor T. Nothing has changed in the circuits of the transistors T ₁ and T_ because no alternating current flows through the circuit of the transistor T_, the transistor T- is excited by the difference in the alternating current voltages on the collector of the transistors T "and T ₁ and in the considered case, this difference is zero.

A reception signal in the form of the voltage U ₁ may now appear on the collector of the transistor T ₁ , coming out of the line. He superimposed on the collector of the transistor T to the output signal and provides the front-mentioned difference in the change represents voltages _t have turned the transistor T ^, on the input impedance Z of the receiver H we get an AC voltage

ΓΪ θ

nearly

^U H ^{= U} 1

^Z 5

amounts to.

H Accordingly, depending on the ratio j, the reception will be signal

carried out from the line to the receiver with some amplification or weakening.

- 5th

In the case observed above, i.e. when equation (1) is met, the output signal is not passed to the receiver. However, as is well known, some adequate level of eavesdropping is required. Optimal hearing loss is achieved Mainly by deviating appropriately from the condition given in equation (I).

When receiving, the input impedance of the circuit of the transistor T is approximately equal to the emitter impedance Z _E , x-reii, the received signal reports with it on the series with the emitter circuit. The input impedance of the output amplifier, with the entry on the collector of the transistor T-, is incomparably greater than the Z ₁ - * and its influence can be insignificant. This is why the input impedance of the entire circuit arrangement, viewed from the connections of the line (L ₁ , L-), is approximately equal to Zj-. For the purpose of matching the impedance of the line (Z,.) Should be approximate

We move on to FIG. 2. As an example, there is one of the many possible design variants of the arrangements, many marriages dat Scheme according to FIG. 1 is equivalent, listed. The supply is carried out by means of stable power sources. Also shown are graphical solutions for the receiving circuit H as well as' ε-üf- for the transmitter circuit M, which are suitable for the telephone set.

With regard to the equivalent circle of the alternating currents, only thermal resistances, respectively R and R *, are taken for the impedances Z and Z of the balancing amplifier. For the emitter impedance 2 .. the parallel connection R "and C _? taken.

The circuit is fed with direct current by means of four current sources, which are only indicated and which emit _{stable direct currents I-, I 1} - , I- "and I, _o.

IO IX LZ IJ

The condensers C, _f C ₇ and C x * / have large capacities.

The microphone circuit M is implemented by means of a charcoal milophone M,

e
which is fed with stable direct current I-. The alternating voltage

- 6-

is fed through the capacitor C to the connection of the bases of the transistors T ₁ and T ″.

Receiver circuit H is the listener H with the coupling capacitor C ₀

e ο

The resistor R ₀ , which is required in the DC circuit, has

a resistance that is significantly greater than the impedance of the listener "

The sources of stable direct currents have very large dynamic Resistances that prevent undesired coupling. (In the exemplary embodiment shown in the following FIG dynamic resistances greater than Io MOhm are achieved). Therefore, when considering the equivalent circle for Alternating currents the power sources are not taken into account.

The inlet impedance (Z _1. ) Of the telephone line can be roughly approximated with a parallel connection of the resistor R_ and the condenser

Yy

sators C_, as shown in the drawing.

L

The collector of the transistor T _{1 of} the output amplifier is connected to the end L in line for the alternating current via the large capacitance C i. The resistance R _fi required in the direct current circuit is significantly larger than the R i and can be neglected in the alternating current circuit (or deducted in an equivalent R _T ).

Ij

In the case under consideration (compared to FIG. 2 with FIG. 1), it is structured the equation (1) into the following equations:

^R 4 = ^R L

(3)

In contrast to equation (1), where Z _T is the exact value

Li

the line impedance is assumed, which is why it was a condition for the complete elimination of the sound, the above two equations (3) are the condition for optimal back loss, because they _{are derived on the basis of the Z T} , which is a rough approximation

Li

mation of a mean value for different telephone lines (es a procedure is used that has been proven in many years of practice

in the determination of the balancing impedance in the case of classic Telephone sets with differential transformers).

The emitter impedance Z ₁ . of the transistor T- is here in the form of the parallel connection R and C _x . carried out- in order to match the impedance of the telephone line, and according to the consideration in connection with equation (2) which reads Z ₁ . = We get Z here

^R 5 - ^R L '

^C 5 ⁼

All resistances in the circuit, as well as the amperage of the The stable direct currents mentioned are provided in such a way that the transistors operate in an optimally active regime. On the other hand, they are Resistances are calculated in such a way that they simultaneously meet those listed above Meet the conditions necessary for the AC circuits to work.

Let us move on to FIG. 3. Inside is the electroacoustic Composition of the telephone set is shown, which is carried out by means of the circuit from FIG Dialing device, as well as the devices of the call indicator, because they are meaningless in the matter observed).

The circuit is ^{fed with equals 1} wi from the telephone line (L ₁ / L) via a Graetz rectifier bridge G by means of sources of stable direct currents, which are shown in detail in the drawing.

The Grätz rectifier is set so that one can, independently of the polarity of the line ends, the polarity required to supply the circuit gets. In the AC circuit is its dynamic resistance is insignificantly small.

The circle that is shown in FIG. 3 to the left of points 1 and 2 is a bipolar, low voltage transistor stabilizer in accordance with our US Pat. No. 4,321,524 to Prioriiäb from the patent application in Yugoslavia from 16.1o. 1978. The invention is registered in the Federal Republic of Germany.

The aforementioned voltage stabilizer has a voltage characteristic similar to the characteristics of the zener diode. In the dar-

It is used in the same way as the Zener diode is used, but in the area of Ndaäer voltage and low currents _A for which area a corresponding Zener diode cannot be produced. Its main advantages are as follows:

• - The stable voltage (which is analogous to the nominal voltage of the Zener diode is) is very low. It can have any fixed value in the range of 0.7V- - 1.2V, which is most of the time The type of diode used (D-) depends.

- The current working range is very wide.

- The dynamic resistance in the current working range is very small and this in the size range of 1 ohm, one can easily achieve that they are in the majority of the work area < and at lower currents that is practically zero.

- It does not make any noise that occurs with the Zener diode.

- The lower limit of the current working range at a stable voltage of around ο / 7 V is around 2 Mkro A, and in the case of the stab * - With a voltage of around 1 V, it is around 0.1 mA.

To explain how the current sources work, we will use a voltage stabilizer as an example, the off

^R l - BC 4 KOhm T ₄ - BC 212 ^T 5 - AAZ 182 ^D l 21

is composed

(Germanium gold wire diode AAZ 21 is the same as the diode OA 1182 from Tungsram).

The voltage stabilizer mentioned above has a stable voltage U = 1 p6 V, already at the current I (see Fig. 3) about 0.1 mA

issued with dynamic resistance Δ Ό : I of about

1 ohm. For currents I, which are of the magnitude 1 mA, the dynamic resistance is practically zero,

With U-2 we become the instantaneous value of the voltage between the ends L. and L_ denote. - 9 -

The voltage stabilizer is fed with the current by means of the resistor R._, which is dimensioned so that ^{the current} I ^{exceeds the} value of _{0.1 mA even at the lowest voltages ^ 12.} It can therefore be assumed that the stable voltage U is independent of the voltage 2L ₁ O ^5anz.

The stable direct current I- is due to the voltage U and the

Resistance R _{1 is} determined. One has
Io

¹ Io ^ ^{ü o - ^U BE> ^{: R} lo

Large resistance for the compensation R "improves the stability. When using a standard resistor R_, ie without any adaptation, one obtains dynamic resistance all- _n ;

J- Δ f

Λ I " which belongs to the number Io MOhm. Io

The same applies to the other three power sources. Accordingly, it is justified that when considering the alternating current circuits, the influence of the current sources: I, I ₁ -, / I ₁₂ ^ηη & ¹ Io was neglected.

In the meantime, when determining the impedances Z n and Z ₁ . it should be taken into account that in the AC circuit the resistors R, g and R, connected in parallel at the ends of the line. L. and L "appear. This also applies to the resistances R ^ rr _{un (} j R ^ _{3 x} and they should also be taken into account, although they are very large.

The whole system according to Fig. 3 must be planned so that it works even with "the smallest voltages" 2 ^ ₁₂ between the ends. (L-, Lu) appear in the case of the longest telephone lines. The case of the voltage on the Grätz rectifier should also be taken into account. For the transistor circuits of the transistors T., T.sub.n and T to function properly, certain voltages must not fall below a lower limit. In the observed case, the voltage in one direction on the collector of the transistor T- is critical. Therefore, it is of great importance "that the fewer passes to the sources of stable flows of the available voltage 2 £ ₁₂ i ⁿ loss. This problem is solved favorably thanks to the fact that our voltage stabilizer emits a small voltage U with low power consumption.

Namely, the voltages on the emitter resistors of the transistors

- Io -

the power sources are U -U_. . Assume that U = 1 V and U__ =

ο £> e ο HL

o, 6 V, they amount to o, 4 V "The transistors of the current sources operate in the area where they in a sense _BE ^U ^ ^U _CE is.

The minimal U _, _ is about o _r 2 V ,, which together with the mentioned ο, 4 Vj, ο, 6 V results. Namely, in the critical case of the lowest values of the voltage IC ₁₂ '^ ^e system will work well until 0.6 V can still be drawn from the available voltage for the work of the power source.

The formula (1) is carried out under the condition _A that the quotients Z, ί Z- and Z _T : Z are "small" They should be smaller than Io so that the influence of the parameters of the transistor could rightly be neglected. As already said, these quotients represent voltage gains of the balance and output amplifiers. In the case where the carbon microphone is used in the manner shown, no amplification is required because it gives off a sufficiently strong signal Ctyq). One can estimate that for the optimal level of the signal that is conducted on the line, the stable DC current I (with which the microphone is fed) should not be higher than 2 mA.

In general, the shortcomings of the carbon microphone are: short lifespan, loud noise and non-linear degeneration. But, one only has in mind its application in the classic Telephone set where it works as the only amplifier overloaded. Meanwhile, by feeding the gas with a very weak one constant direct current, we have eliminated the deficiencies mentioned. Its duration is considerably lengthened, and the noise and nonlinear distortion are greatly reduced. Accordingly it can stay with its advantages, which are that it works as an amplifier and that it is cheap and light ..

Given that the signal from the carbon microphone is proportional is the direct current with which it is fed, in the case of the classic Telephone set, with a longer telephone line, there is a weaker signal - which is unfavorable. By feeding with constant Electricity achieves that its signal is independent of the length of the telephone line, which is better.

However, the circuit of Fig. 3 enables an automatic control of the level of the microphone signal, namely such that

- 11-

the longer the line, the stronger the signal. ' Namely, instead of the compensation resistor R ₀ , a two-pole transistor cutter is to be used, which represents an equivalent inductance and which are approximately represented with series inductance and resistance. The inductance of this circuit should be so great that it does not have any influence on the work of the equivalent circuit for alternating current. The resistance should be smaller than the value that was required for the R "so that the current I, fully

Zo Io

would be constant all the time. With such an equivalent resistance one achieves that the current I _{1 is} no longer constant, but

Io

that it decreases with the increase of the direct current voltage on the ends of the telephone set _t that is, with the shortening of the telephone line (and vice versa). The consequence is that the longer the streamline I ₁ becomes stronger, consequently the signal from the microphone will also be stronger. With a sufficiently large equivalent inductance, the current I contains practically no alternating current of the audio frequencies.

In the variant embodiment of the circuit according to FIG. 2 (and Fkg.3), the condition from formula (1) is fulfilled in such a way that the impedance Z _{0 is} complex, that is to say that it is defined by parallel R ₀ and

4L * ά *

C _{0 is} executed. It can easily be seen that the amplification of the output amplifier is independent of frequency, which means that there is no linear distortion. The prerequisite is that the capacitances C ″ and C _{ß are} so large that there is no weakening of the low frequencies.

The formula ■ (·!),. which indicates the balance of the balance and output amplifiers can also be satisfied in various other ways. For example the variant in which: the impedance Z _{0 is} only in the form of the thermogenic resistor R ₀ , the impedance Z_ also only with R ,, and 1, in the form of parallel connection of the resistor R. and the capacitor C. The formula (-1) can now be broken down into the following two equations:

^R 4 ^{: R} 3 ^{= R} L ^{: R} 2 7

CC = R - RJ .C ₄ . C _L R ₂ . R ₃ ^

However, it is easy to see that the amplification of the output amplifier is now dependent on the frequency. The microphone signal is amplified by the linear distortion in such a way that

higher frequencies are pushed back. The frequency characteristic can be improved by reducing the capacitance of the condensing capacitors C _fi and C “(which can therefore be geometrically smaller and cheaper).

Claims (3)

PATENT CLAIMS φ. Transistor fork circuit for telephones, whose entire equivalent electrical circuit for alternating current consists of three transistor circuits, namely the output amplifier with the transistor T-, the emitter of which is connected to one end of its emitter impedance Z "and its collector is connected to one end of the input impedance Z ₁ . the telephone line, which consists in the collector circuit, further from a balancing amplifier with the Trara disturb T ₂ * whose emitter with one end of its emitter impedance Z_, and its collector with one end of its collector impedance Z ₄ , and finally from the circuit of the transistor T. ,, whose emitter with one end of its emitter impedance Z ₁ . * and its collector are connected to an input end of the receiver H, the other end of which is connected together with an output end of the resistor M at a common point together with those emitter and collector impedances mentioned above which are not connected to corresponding ends of the respective transistors, thereby characterized in that the base of the transistor (T-)., In whose circle the receiver (H) is attached, is connected to the collector (Τ «) of the balancing _{amplifier and the emitter via its emitter impedance (Z 5} ) with the collector of the transistor (T ..) of the output amplifier is connected; that the emitter impedance (Z) is designed so that one achieves sufficient matching of the input impedance of the entire telephone circuit of the impedances (Z_) of the telephone line, from the output of the emitter (M) to the bases of the transistor (T ₁ ) of the output amplifier and the Transistor (T ₂ ) of the balancing amplifier, be it which direct or indirect way the signals that are exactly the same "are supplied, the quotient of the input impedance of the telephone line (Z _T ) and the emitter impedance (Z _n ) of the output amplifier Jj £. is almost equal to the quotient of the collector _{impedance (Z 4} ) and emitter impedance (Z-) of the balancing amplifier, and approximately equal to the extent to which this is necessary to achieve sufficient back loss. 2. transistor fork circuit according to claim 1, characterized in that in the balancing amplifier its impedance (Z.) as a thermogenic resistor (R ₄ ) and its emitter impedance (Z ^) as a thermogenic - 14 - ... OZ ^ JDU / Resistance (R_) are executed, where the emitter impedance (z_) • 3 2 of the output system are designed as parallel connections of thermogenic resistance (R ") and capacitance (C ₀ ). 3. transistor fork circuit according to claim 1, characterized in that in the balancing amplifier its collector impedance (Z.) in Fort of parallel connection of the thermogenic resistor (R.) and the capacitance (C.), and its emitter impedance (Z-) as a thermogenic resistor ( R-) are formed, the emitter impedance being designed as a thermogenic resistor (R ₀ ). copyJ