SU439895A1 - Dual Balance Modulator - Google Patents

Description

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The invention relates to modulators and can be used in amplitude and phase modulation devices, signal multiplication devices, and other radio devices.

A double balanced modulator is known which contains a phase inverted cascade on a transistor covered by parallel feedback, whose input is connected to a signal source, and an electronic switch controlled by a source of carrier frequency.

The disadvantages of the known balanced modulator are the poor suppression of the carrier frequency and the lack of suppression of the modulating signal.

In order to improve the suppression of the carrier frequency and the modulating signal, the series-connected resistors are inserted into the emitter circuit of the phase-inverse cascade transistor in the proposed modulator, in parallel with one of which an electronic switch is connected.

The drawing shows a schematic diagram of the described modulator containing a phase-inverse cascade on transistor 1, enveloped by parallel feedback through a resistor 2, the input of which through terminal 3 is connected to a signal source, two series-connected resistors 4 and 5 in the emitter circuit of the transistor of this stage, and

output terminal 6. Parallel to the resistor about the electronic switch on the transistor 7, the base of which through terminal 8 is connected to a source of carrier frequency.

The modulator operates as follows. The signal from the input terminal 3 is fed to the output terminal 6 through a phase-inversion stage on transistor 1 and through a parallel feedback resistor 2. These signals at the output terminal 6 (the first with respect to the second) have a phase shift of 180 °, since transistor 1 is connected in a circuit with a common emitter. In the usual amplifier mode, when the sum of the resistances of resistors 4 and 5 is significantly less than the resistance of resistor 2, the signal in the collector circuit of transistor 1 .. prevails,

By increasing the sum of the resistances of the above resistors to the value of the resistance of resistor 2, the signal in the collector circuit and the signal coming to the output through resistor 2 will have the same amplitude and opposite phase, and the total signal at the output will be equal to zero.

With a further increase in the sum of the resistances of the resistors 4 and 5, the output of the signal passing through the resistor 2 of the parallel feedback circuit will prevail.

The transistor 7 of the electronic key closes in time with the incoming to its input (terminal

8) by the carrier signal, the resistor 5, as a result of which the total resistance of the series feedback circuit can vary in such a way that its ratio to the resistance of resistor 2 will be less or greater than one. In this case, the resistances of resistors 4 and 5 can be chosen such that the amplitude of the output signal before and after the phase change has the same value. If, using an electronic key, the ratio of the resistances of the serial and parallel feedback chains is changed from a value less than one to a value equal to one, the output signal will almost fall to zero.

In a double balanced modulator, the suppression of the modulating signal and carrier frequency can reach 40-60 dB.

Subject invention

A double balanced modulator containing a phase inversion cascade on a transistor covered by parallel feedback, whose input is connected to a signal source, and an electronic switch controlled by a carrier source, characterized in that, in order to improve the suppression of the carrier frequency and the modulating signal, The emitter circuit of the phase-inverter cascade is connected in series by resistors, in parallel to one of which the above-mentioned switch is turned on.

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