SU627560A1 - Balanced modulator - Google Patents

Description

The invention relates to radio engineering, in particular, to devices for amplitude modulation of high-frequency oscillations, and can be applied in radio transmitters using amplitude or single-band modulation with a suppressed carrier.

Modulators are known that are made on two or four nonlinear TSjt elements, for example, semiconductor diodes or varicaps, which are included in the LIJ balanced circuit. In such modulators fom, achieving good balancing requires the selection of nonlinear elements with as close as possible parameters.

Of the known devices, the most conspicuous to the invention is a balanced modulator, implemented in a T-shaped bridge circuit and containing one non-linear element. The sequential gel branch of the T-shaped bridge circuit is formed by the active resistance shunting the differential induction coil with the middle output, and the parallel branch is formed by a nonlinear

a switching element, such as a transistor, which is switched on by a middle coil output and a common drive

U

The disadvantage of this modulator is the low input impedance for the modulating signal, due to the low resistance of the switched element, as well as a decrease in the accuracy of balancing at high carrier frequencies due to the influence of parasitic capacitances in the branches of the circuit.

The aim of the invention is to increase the input impedance and improve balancing at high frequency.

Claims (2)

This peg is achieved by the fact that in a balanced modulator made according to a T-shaped bridge circuit containing a differential inductance coil with a midpoint, to the input of which are connected in series sources of modulating and modulated voltages, capacitor-switched base voltage, for example, on the divider. voltage and capacitor. A varicap is connected between the midpoint of the inductor and the source of the mix. The diagram shows a circuit diagram of a balanced modulator. The balance modulator, which is complete according to the T-ra-bridge circuit, contains a differential inductance 1, which is amplified by a capacitor 2, which forms a series of a T-bridge bridge, and the midpoint of the inductance is connected to a varicap 3, which forms a parallel branch of the circuit, and a varicap displacement source made on a voltage divider 4 and a capacitor 5. Series-connected modulating mixix 6 and modulated voltage 7 are connected to the input of the inductor coil. The output of the inductor is output 8 of the modulator. The modulator operates as follows. In the presence of a modulating signal from source 6, the displacement on the varicap 3 is selected using a voltage divider 4 such that the capacitance of the varicap 3 is equal to the quadruple capacity of the capacitor 2, and the T-shaped bridge is balanced and the voltage of the carrier frequency 63 at output 8 is absent . When applied to a varicap 3 of modulating voltage with a frequency L, the capacity of the varicap decreases with a positive half-wave of this voltage and increases with a negative one. A decrease in the capacitance of varicap 3 causes a voltage at the outlet 8 of the hens with a phase that coincides with the phase of the hen at the input, since in this case the current through the serial branch of the bridge with the capacitor 2 prevails. An increase in the capacity of the varicap causes the appearance of voltage at the output 8 carrier with the opposite phase, since in this case the current through the parallel branch of the bridge with varicap 3 and cjTuxy of inductance 1 prevails. Thus, balanced modulation takes place, and on. The modulator 8 outputs are allocated side frequencies with Si., Thank you to the use of reactive elements, varicap 3 and capacitor 2 in the arms of the bridge, there is practically no loss of signal energy in the modulator, which increases the efficiency of the modulator. The resistive and reactive resistances of a varicap operating at a blocking voltage of a room are quite large for a low frequency of oscillation. This provides a high input impedance modulator. In phase systems of forming a bi-band signal, for example, a modulating signal can be fed to a modulator directly with a high-frequency low-frequency phase shifter, which considerably simplifies the circuit. The parasitic capacitances of the modulator, for example, the capacitance of the installation and the capacity of the winding inductance coil, are stranded with the capacitances of the shoulders of the bridge and can be taken into account when choosing the latter, therefore such parasitic capacitances of the circuit do not impair balancing. The modulator is balanced by varying the displacement on the varicap, which eliminates trimming elements from the high-frequency part of the modulator, and, therefore, provides a good shielding of the modulator. In an experimental test of this balanced modulator at a non-dry frequency of 27 MHz, with a carrier amplitude at the input of 1 V, the total amplitude of the side bands of about 0.35 V. was obtained. The varicap D901G was used with a mixing voltage of 6 V and the amplitude of the modulating voltage, April 4 V. The suppression of the carrier more than 40 dB was easily achieved. Claims of the invention A balance modulator made according to a T-shaped bridge circuit containing a differential inductance coil with a midpoint, to the input of which are connected in series sources of modulating and modulated voltages, capacitor-backed by capacitor, varicap, bias source, made, for example, on a voltage divider and a capacitor, due to the fact that, in order to increase the input resistance and improve balancing at a high carrier frequency, varicap is connected between the point of inductance and source of bias.: Sources of information taken into account in the examination: 1. Kopylov K., F. and Terpugov N. V. Parametric capacitive low-frequency amplifiers. M., Sov.radio, 1973, p. 11, fig. 1.4. 2. The patent of England No. 1084587 cl. H 03 R., 09.06.65.