SU60400A1 - Duplex telephone amplifier - Google Patents

Description

As is well known, the operation of existing types of duplex amplifiers with a balanced circuit is based on the use of a differential system. The differential system is a conventional bridge and is connected at the input of the amplifier between the line and the balanced circuit. Reinforcing elements, giving a gain in both directions, are included in the diagonal of the bridge, and this is achieved by eliminating the interaction between the latter. The main condition for the operation of a duplex amplifier with a balanced circuit is full compliance of the input resistances of the line and the balanced circuit throughout the whole spectrum (Transmitted frequencies. The latter circumstance is the main drawback of the duplex amplifier if the latter operates on air lines whose input resistance depends on external conditions The same circumstance makes it impossible to use duplex amplifiers of this type in linear-selective communication conditions, when the number and location of the included in According to the invention, in the proposed duplex telephone amplifier, for eliminating feedback without using a balanced circuit, the auxiliary amplifier line is turned on so that the talk currents of one transmission direction, amplified The main and auxiliary amplifiers created equal magnetic fluxes of the opposite direction in the differential transformer. In the scheme of the proposed duplex telephone amplifier, the letters U and U4 designate the main amplifiers, U2 and UZ - auxiliary amplifiers and MTi and DGa-differential transformers. The diagram shows that the differential system is separated from the line and switched on at the output of two amplifiers, one of which is main and the other auxiliary. The inputs of both amplifiers are connected in parallel. If the gains of both amplifiers are the same, then the voltages at the outputs of both amplifiers will also be the same, which means that the currents in both windings of the differential transformer will be the same. If the primary windings of the differential transformer are also the same, and the windings of the latter are opposing, then the flows created by these windings will be reciprocated: BUT compensated. On the secondary winding of the differential transformer e. D.S. will not be induced. This corresponds to the condition of complete balance in amplifiers with a balanced circuit.

Line is connected between the first and second stages of the main amplifier.

Since the main condition for the operation of this circuit is the equality of the gains of the main and auxiliary amplifiers, the problem of a duplex amplifier of an unbalanced loop is to create an amplifier circuit in which the gain would not depend on the input of the linking circuit, which is switched on in some way between the amplifier stages.

Solving the latter problem is not difficult and may have many options.

It is very convenient to use the principle of negative feedback, in which, as is well known, the gain of an amplifier almost does not depend on its own amplification of the same amplifier. With a sufficiently deep negative connection and provided that the line is turned on via a small extension cable, quite satisfactory results are obtained. The same problem is much more completely solved by the use of special bridge circuits.

It is not necessary that the amplifiers of both amplifiers — primary and secondary — be the same. They may be different if you have correspondingly different coils of a differential transformer. You can always have a single-stage auxiliary amplifier with a two-channel main amplifier.

The effect of the proposed amplifier is as follows: the voltage from the LI line falls on the second stage of the amplifier Y. The first stage serves as a buffer, thanks to

210

which this voltage cannot reach the input of the auxiliary amplifier Vg.

The voltage amplified by the first cascade falls into the winding of the differential transformer DG, and, not compensated by the second winding, induces e. d. at points a-b. This uh. d. gets into the parallel-connected inputs of the main and auxiliary amplifiers UZ and Y4, then amplifies and enters the primary windings of the second differential transformer DT. Since the transformer windings are connected in opposite directions, the currents are also compensated for in the secondary circuit at points c - d e. d. will not be induced.

The voltage amplified by the first cascade of the main amplifier V4 falls into the line L. The same will happen when the circuit is operated in the opposite direction.

There can be no perfect compensation in the windings of a differential transformer, just as it does not exist in existing amplifiers with a balanced circuit. However, this circumstance is not an obstacle to their widespread use.

The proposed circuit has the advantage that its operation does not depend on the input impedance of the line, and it can be widely used in all cases where the use of a conventional amplifier is not possible or is rather difficult. This is especially true for multifrequency communications, where, as is known, the use of a bala contour is not possible.

The drawback of the circuit lies in the presence of four amplifiers instead of the two available in a conventional duplex amplifier.

Subject invention

1. Duplex telephone amplifier, characterized in that, in order to eliminate the effects of feedback without the use of a balanced circuit, LII1NI auxiliary

the amplifier is switched on so that the talk currents of one transmission level, amplified by Smzsdany and auxiliary amplifiers, create equal magnetic fluxes of the Opposite direction in the differential transformer. 2. Form performance amplifier

Claim 1, characterized in that the main and auxiliary amplifiers have different amplification factors and their difference is compensated by the appropriate selection of the windings of the differential transformer or by another known method.