DE2807304A1 - AMPLIFIER WITH SYMMETRIC BRIDGE CIRCUIT - Google Patents

Description

Licentia Patent-Verwaltungs-GmbH
6000 Frankfurt (Main) 70

Ulm (Danube), l6. Feb. 1978

NE2-UL / Sar / rß UL 77/1

Amplifier with symmetrical bridge circuit;

The invention relates to an amplifier with a symmetrical bridge circuit for controlling an electroacoustic, electromagnetic or electrodynamic converter, one fed from a subscriber line, two Terminal having terminal of a telecommunications system.

As is known, the pair of elements K1, K2 is a subscriber terminal or another device of a telecommunications system fed from the line loop at the same time output and Power supply connection. This circumstance requires special properties from electronic components for such system parts, which can be described as freedom from interaction. One of them may be in contact with the pair of terminals from the outside AC voltage not one fed by the line loop affect the internal amplifier of the terminal and an alternating voltage generated internally by an amplifier of the terminal must not reach the output terminals of the end station.

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On the one hand it is for the sake of Heicimeite and the associated conductor material costs on small loop currents down to 10 mA interested., On the other hand, Z is ₀ B ₀ designed as a high-quality dynamic earphones elektroakustisehe converter realized "only with expensive Magnetitferkstoffen, priced converter with sintered magnetic materials have j @ - but the sensitivity is lower by a factor of 2 to 3 and therefore require an additional amplification of the loop alternating current.

There are already numerous feedback-free amplifier circuits for the above Purpose known. However, they all have the disadvantage that they use the loop direct current take advantage of it badly.

The invention is therefore based on the object of specifying an amplifier of the type mentioned at the outset, which with low Direct current feed has a high efficiency, and is monolithic in a simple manner and therefore inexpensive can be integrated.

The task is achieved in an amplifier of the type mentioned by the combination of the in the characterizing part of the Claim 1 mentioned features solved. The invention now makes it possible to use the subscriber connection line fed electroacoustic or electromagnetic transducers without any repercussions on the exchange with essential to control better efficiency.

Advantageous refinements and developments of the invention are specified in the subclaims. In the embodiment of the invention according to claim 2, the amplifier is with only Little space requirement can be implemented with modules available on the market.

9834/0426

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The embodiment according to claim 3 is taking up little space integrable components can be realized.

The development according to claim 5 ensures stabilization the working point of the bridge amplifier, so that there is always an optimal, interference-free output power of the converter is attainable. An advantageous embodiment of the stabilization circuit is specified in claim 6.

The absence of interference of the proposed amplifier is essentially achieved by a constant current source. These Constant current source can be used in conjunction with the symmetrical bridge circuit be switched. However, it is much more advantageous to design it according to claim 7, since then the bridge circuit The maximum possible operating voltage is available to control the converter and therefore the best Efficiency of the amplifier according to the invention can be achieved.

The invention will now be explained in more detail with reference to exemplary embodiments shown in the drawings. It show in detail;

Figure 1 basic circuit of the amplifier according to the invention

FIG. 2 circuit of an amplifier composed of two monolithically integrated push-pull amplifiers according to the invention

Figure J circuit arrangement of a monolithic integrable Amplifier according to the invention

Figure 4- Circuit arrangement of a monolithically integrable amplifier that takes up little area according to the invention

909834 / 0A2S - 7 -

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Figure 5 stabilization circuit

FIG. 6 circuit arrangement of an amplifier according to the invention requiring little area and supply current,

In Figure 1 is a basic circuit of the invention Amplifier shown. The symmetrical bridge circuit consists of the bridge elements designed as current sources 2 to 5. A converter 1 is with its one connection A at the connection point of the bridge elements 2 and 3 and with its other terminal B connected to the connection point of the bridge elements 4 and 5. The bridge elements are from a voltage source of the subscriber line fed via the terminals K1 and K2 of the subscriber terminal in which the bridge circuit is installed is. Due to the voltage drop at the internal resistance of the exchange-side supply voltage source and the connection line As a result of the current through the terminal point, the operating voltage Ug "

It is a feature of the invention that the bridge elements 2 to 5 can be controlled linearly and crosswise so that their currents I ₂ = Ic and I, = I ^, with at least one device for keeping the constant through the terminals

see is. K1 and K2 flowing current before / It must therefore be ensured that both the total currents Ip + I ^ = I * + Ir remain constant even when the converter 1 is modulated. A circuit designed in this way has the advantage that the available direct current I = I ^ + I ^ is fully utilized. At the same time, such a circuit produces ideal hearing protection, since no current greater than I can flow through the converter 1 when the current sources are overdriven.

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A first embodiment of the basic circuit shown in FIG shows Figure 2. Here, the bridge elements, not shown, output stage transistors are monolithically integrated Push-pull amplifiers 60 and 70, their respective Output A and B of the converter 1 and at their respective input a signal source causing an anti-phase modulation E is connected. The device for keeping the current flowing through the terminals K1 and K2 constant is here a constant current source 8 connected to the feed line of the bridge amplifier -10. Serves as a signal source For example, in a terminal the connections of a hybrid circuit to which the very sensitive and therefore expensive converters are connected.

The constant current source 8 brings about the desired constant current through the two amplifiers 60 and 70 and thus freedom from interaction of the alternating current through the converter 1 to the current through the terminals K1 and K2.

A creation design for a circuit according to FIG. 2 is shown in FIG. its working resistance 62 and its emitter resistance 64 _t controlled in phase opposition. The base of the driver transistor 63 is connected to one terminal E1 of the signal source.

The other connection of the converter is controlled by the bridge elements, which are also designed as transistors 51 and 71, which is also in phase opposition through a second driver circuit with the transistor 75 »its working resistance 72 and its emitter resistor 74- are controlled. the

90983WCH26 " ⁹ "

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The base of the driver transistor 73 is connected to the other terminal E2 of the signal source ,, The current for the bridge circuit including the driver circuits is kept constant by a constant current source 8 located in legs with the bridge circuit ,, As a constant current source, for example, a transistor circuit known per se can be used _o

The driver amplifiers advantageously reduce the input current of the amplifier here. Your gain is to be set so that (Ι, -Ιο) B. - U _BC - TJ. _c , where E. is the DC resistance of the converter and U _{BC is} the voltage between points B and C and the voltage O » _{c is} the voltage between points A and C of the circuit shown in FIG. In smaller gain is not the entire current difference I _5, would - Ip flow through the transducer 1 _o at greater

^ 5 Gain is with a modulation-dependent operating point shift expect a fluctuating internal resistance of the amplifier.

The advantage of this circuit is that it takes up less space the six transistors. The resistors 32 and 52 in the emitter leads of transistors 31 and 51 and the resistors 64 and 74 in. The emitter leads of the driver transistors 63 and 73 serve to linearize the circuit and for symmetry of the currents flowing in both branches of the bridge.

The transducer is controlled in FIG. 3 with a relatively low resistance due to the emitter circuit of the transistors 61 and 71. The fact that the acoustic parameters of electroacoustic transducers are usually designed for this low-resistance operating mode speaks in favor of operation of the transducer from a finite internal resistance. This is countered by the high temperature coefficient of the resistance of the copper coil of the transducer. A transducer resistance of for example 200 0hm at 25 ° C is at -25 ⁰ C and about 160 0hm at +60 ⁰ C for about 228 0hm. The power to the

909834/0426

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Transformer coil, however, is proportional to the current, so that a Current impression enables a constant transfer factor over the entire temperature range.

An embodiment of the invention, which modulates the converter with high resistance, is shown in FIG. 4. It largely corresponds to FIG Basic circuit according to FIG. 1, since all bridge elements represent current sources here. The lower half of the in figure 4 is practically identical to that of FIG.

The bridge elements 2 and 4 of the acting as current sources FIG. 1 is shown in FIG. 4 as transistors 21 and 41, respectively, of the opposite conductivity type to the bridge transistors 31 and 51 formed. This is the collector of the transistor 21 connected to the terminal A and the collector of the transistor 41 to the terminal B of the converter 1, so that by the Bridge circuit the converter is driven with high resistance compared to its alternating current resistance.

The base connections of the bridge transistors are crossed by a respective driver circuit 22 to 25 or 42 to 45 controllable. A driver circuit consists of a driver transistor 24 or 44 and a current mirror with the Transistors 22 and 23 or 42 and 43. The respective current mirror is fed by the collector current of the splitter transistor assigned to it and is effected at the same time by the Transistors 23 and 43 a current gain, so that for example with a low collector current and thus a low control current for the driver transistor 24 of the essential larger collector current of the bridge transistor 21 can be controlled is. In this way, the driver circuit can advantageously be implemented with small-area transistors »

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The area ratios of transistors 21 and 23 or 43 and _o 41 are selected so that the low Kollektorström® of the driver transistors 24 or 44 _o to the required full scale of the converter 1 bridge currents I "or I _o ^ increased. In this Heise the equality of the bridge currents in transistors 21 and 31 or 41 and 51 _o enforced so that only flowing through the transducer 1 through the modulation of the signal source related difference current.

Since it is difficult to integrate PEJP transistors with high Current amplification factor (B «-40) can be realized at around 5mA the transistors 23 and 43 of the current mirror circuit are preferably designed as substrate transistors, i.e. as transistors, whose collector is usually at reference potential and is thus formed by the substrate.

Due to the series connection of two transistors 21 and 31 or 41 and 51 acting as a current source, the electrical potentials of the converter connections A and B undetermined. To achieve a level that is always distortion-free of the converter, it is therefore advantageous to provide a stabilization circuit that reduces the potential of the connections of the converter holds at its setpoint.

A simple circuit for this stabilization is shown, for example FIG. 5. This stabilization circuit has a double collector transistor 91. The one collector this transistor is connected to terminal A of the converter and to a resistor 93. The other collector is connected to terminal B of the converter and to a resistor, the other end of which is connected to the other end of the resistor 93 is connected. These resistors 93 and 94 have equal resistance values, so that the connection point of the two resistors as a center tap of a single one

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Resistance can be understood, and is also realizable in this way.

The base of the double collector transistor 91 is via a Resistor 92 and the emitter are connected directly to a line leading to the connection source K1 (FIG. 4). Further there is a constant voltage source between the base of the transistor and the center tap of the resistors 93 and 94 "for example a series of diodes.

Are the collector currents of the bridge transistors 31 and 51 the one developed further with the stabilization circuit according to FIG Circuit according to Figure 4 is slightly larger than that of the bridge transistors 21 and 41, the voltage between the connections of the converter and point C or the connection terminal K2 lower. This becomes the center tap voltage of the resistors 93 and 94- compared to the terminal K1 higher and Via the diodes 95, the double collector transistor 91 controlled. Its two collectors feed the same currents into connections A and B of the bridge and correct them thereby the potential of the converter to the desired target value.

For the proper functioning of a circuit according to FIG. 4 with a stabilization circuit according to FIG Effectiveness of the stabilization, i.e. also when the potential of the connections A and B is shifted in the opposite direction Direction, expedient to design the circuit so that the collector currents of the transistors 31 and 51 from the outset are slight are larger than those of the transistors 21 and 41, so that the collectors of the double collector transistor 91 always carry some current and thus tapering to the mean potential of connections A and B can act.

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A circuit of an amplifier according to the invention that makes use of the entire standing for jointing clamp voltage Ug (refer _o FIG 1) between the terminals K1 and K2 for the modulation of the transducer 1 and has thus an optimum ¥ irkungsgrad is _o shown in Figure 6. Here the device designed to maintain a constant by the terminals K1 and K2 current flowing as a current mirror with the transistors 35 and 36 or _o 55 and 56 ,, These current mirrors are controlled by the series connection of an opposite phase from the Signalquslle e through the terminals E1 and Ξ2, of the transistors 37 and 57 existing differential amplifier with a constant current source 81 arranged in the feed line of the differential amplifier bound «,

The collector currents of transistors 37 and 57 of the differential amplifier flow into the current mirrors 35 and 36 or “55 and

56. The base voltage of the current mirror transistor 35 or controls the collector current of the "lower" bridge transistor 31 or 51 and the collector current of the driver transistor 24 and 44. The remaining part of the circuit shown in Figure 6 corresponds to the circuit of Figure 4 and has the same Function already explained for FIG.

It is also advantageous for the amplifier according to FIG. 6 to additionally provide the stabilization circuit according to FIG. 5, because this allows manufacturing tolerances to be absorbed and thus consistently optimal reinforcement properties be achieved.

909834/0426

Claims (7)

Licentia Patent-Verwaltungs-GmbH
6000 Frankfurt (Main) 70 Ulm (Danube), l6. Feb. 1978 NE2-UL / Sar / rß UL 77/15 ^ Patent claims M.) Amplifier with symmetrical bridge circuit for controlling an electroacoustic, electromagnetic or electrodynamic transducer (1) of a terminal of a telecommunications system that is fed from a subscriber line and has two connection terminals, characterized by four bridge elements (2, 3 >> 4,5) that can be controlled linearly crosswise. and by at least one device (8) for keeping the total current flowing through the connection terminals constant, even when the converter is modulated. 2. Amplifier according to claim 1, characterized in that the bridge elements are output stage transistors of two monolithic integrated push-pull amplifier (60, 70) are at their respective output of the converter (1) and at their respective input a signal source causing an anti-phase control (E) are connected. 909834/0426 nwrmM " ORIGINAL INSPECTED - 2 - UL 77 / 154- 3. Amplifier according to claim 1 or 2, characterized in that the bridge elements each consist of two connected in series and transistors (21, 31; 4-1,51) connected to their collectors are of opposite conductivity type, their base connections crossed by one driver circuit each 22-25; 4-2-4-5) can be controlled, which essentially from a driver transistor (24 ·; 44-) and a current mirror (22, 23; 4-2, 4-3), where the respective current mirror is fed by the collector current of the driver transistor assigned to it and causes a current gain (Figure 4). 4. Amplifier according to one of claims 2 or 3, characterized in that that the device for keeping the current flowing through the terminals constant than in the feed line the bridge circuit switched constant current source (8) is formed. 5. Amplifier according to claim 3 or 4, characterized in that that a stabilization circuit is provided, which the mean value potentials of the connections of the converter (1) on their Setpoint holds. 6. Amplifier according to claim 5, characterized in that the Stabxlxsierungs circuit a double collector transistor (91), whose collectors on the one hand with the two connections (A, B) of the converter (1) and on the other hand through a resistor (93, 94 ·) are connected to the center tap and its base on the one hand via a resistor (92) its emitter and a connection terminal (K1) and on the other hand via one or more diodes (95) with said center tap connected is. - 3 909834/0428 - 3 - UL 77/154 7. Amplifier according to claim 3 »characterized in that the device for keeping the current flowing through the terminals constant as a current mirror (35 »36; 55ι 56) is formed by the series connection of a differential amplifier driven by the signal source (IT) in a counter-based manner (37t 57) with one arranged in its feed line Constant current source is fed. 909834/0426