RU2266610C1 - Frequency mixer - Google Patents

Abstract

FIELD: radio engineering: transceiving equipment; instrumentation engineering: frequency converters.

SUBSTANCE: proposed mixer has transistor VT1 with base mixing circuit set up around resistors R1, R2, power capacitor C1, isolating capacitors C2, C3, C5, parallel LC circuit L1, C4 inserted in collector circuit of transistor VT1 whose emitter circuit incorporates resistor R3 connected in parallel with capacitor C6, the latter being connected to drains of parallel-interconnected field-effect transistors of different types VT2, VT3 whose gates are connected through resistor R4 to ground; their interconnected drains are also connected to ground.

EFFECT: enhanced isolation between input-signal and heterodyne-signal circuit; provision for doubling heterodyne signal frequency.

1 cl, 1 dwg

Description

The invention relates to radio engineering and can be used in frequency conversion in transceiver equipment, measuring equipment.

A mixer is known from the prior art (USSR Author's Certificate No. 1510067, 1987), comprising an input oscillating circuit, field effect transistors having combined sources and drains, a load, a phase shifter, a bias voltage source, a heterodyne signal source. Field effect transistors are used in a passive mode, while the total drain - source conductivity changes. An open voltage is applied to the gates of the field-effect transistors from the output of the phase shifter, which determines the phase of being in the open state of all field-effect transistors, as a result of which the frequency of the input signal is converted at twice the frequency of the local oscillator with improved isolation between the input signal and the local oscillator circuits.

The disadvantage of this type of mixer is the low conversion coefficient caused by the use of field-effect transistors in the passive mode, and the low isolation of the local oscillator circuits and the input signal due to the significant input gate capacitance - the source of field-effect transistors with a p-n junction.

The closest technical solution is a frequency converter (USSR Author's Certificate No. 1020969, 1983), which is chosen as a prototype. This frequency converter contains an input oscillating circuit, two field-effect transistors of the same type, having combined drains and sources, a load, a differential transformer, a heterodyne signal source. Field-effect transistors are used in a passive mode and open at the peaks of the heterodyne voltage coming from the differential transformer twice during the period of the heterodyne voltage, while the total conductivity between the oscillating circuit and the load changes twice during the period of the heterodyne voltage, as a result of which the frequency of the input signal is converted at double frequency local oscillator.

The disadvantage of this type of mixer is the low conversion coefficient caused by the use of field effect transistors in the passive mode, and the implementation complexity caused by the need to use a differential transformer.

The technical result of the claimed invention is to expand the functionality of the frequency mixer, namely, to increase the isolation between the input signal and the local oscillator signal while providing the ability to convert the voltage frequency of the input signal at twice the voltage frequency of the local oscillator signal.

The technical result is achieved due to the fact that the first, second, third, fourth, fifth, sixth capacitors, the first, second, third, fourth resistors, the inductor are introduced into the frequency mixer containing two field-effect transistors, the sources and drains of which are interconnected , the first transistor, a DC power source, and the second and third field-effect transistors are heterogeneous and connected in parallel. In this case, the first terminal of the first capacitor, the first terminal of the first resistor, the first terminal of the fourth capacitor and the first terminal of the inductor are connected to each other and connected to the positive terminal of the DC power source. The second terminal of the first capacitor, the second terminal of the second resistor, the second terminal of the third resistor, the combined sources of the second and third transistors, the second terminal of the fourth resistor are interconnected and connected to the negative terminal of the DC power source connected to the housing. The second terminal of the second capacitor is connected to the second terminal of the first resistor, the first terminal of the second resistor and the base of the first transistor, the collector of which is connected to the second terminal of the fourth capacitor and the second terminal of the inductor connected to the first terminal of the fifth capacitor, the second terminal of which is the output of the intermediate frequency signal. The emitter of the first transistor is connected to the connection point of the first terminal of the third resistor and the first terminal of the sixth capacitor, the second terminal of which is connected to the combined drains of the second and third transistors, the combined gates of which are connected to the first terminal of the fourth resistor and the second terminal of the third capacitor, the first terminal of which is the voltage input local oscillator, and the first output of the second capacitor is the input voltage signal.

The drawing shows an electrical schematic diagram of a frequency mixer, where:

C1 is the first capacitor;

C2 is the second capacitor;

C3 is the third capacitor;

C4 is the fourth capacitor;

C5 is the fifth capacitor;

C6 is the sixth capacitor;

R1 is the first resistor;

R2 is the second resistor;

R3 is the third resistor;

R4 is the fourth resistor;

L1 - inductor;

VT1 is the first transistor;

VT2 is the second transistor;

VT3 - the third transistor;

GB1 - DC power supply;

Input 1 - signal voltage input;

Input 2 - input voltage oscillator;

Output - the output of the intermediate frequency signal.

The first transistor VT1, the first capacitor C1, which is blocking, the second capacitor C2, the fifth capacitor C5, which are dividing by direct current, the first resistor R1, the second resistor R2, the third resistor R3, which determine the mode of the first transistor VT1 by direct current, as well as the fourth capacitor C4 and the inductor L1, which make up the oscillating circuit, form a split-load amplification cascade made according to the scheme with a common emitter.

To the connection point of the emitter of the first transistor VT1 and the first output of the third resistor R3 through a separation sixth capacitor C6, parallel connected field-type heterogeneous second transistor VT2 and the third transistor VT3 are connected, having combined drains, sources and gates, while the third capacitor C3 is connected to the combined gates, which is DC isolation, as well as the fourth resistor R4, which eliminates the possibility of breakdown of the gates of the second transistor VT2 and the third transistor VT3 by static charges In addition, it determines the input impedance of the mixer by input 2. Such a construction of the circuit makes it possible to provide a high degree of isolation between the voltage circuits of the input signal and the voltage of the local oscillator signal, since it allows to obtain a small gate-drain capacitance of the second transistor VT2 and the third transistor VT3, low input resistance amplification stage from the side of connecting the second transistor VT2 and the third transistor VT3 and eliminating the possibility of current flow with the local oscillator frequency in the amplification stage circuits.

The frequency mixer operates as follows.

The voltage of the input signal is supplied to the first input of the frequency mixer, which is then fed through the second capacitor C2 to the input of the amplification stage.

The second input of the frequency mixer receives the signal voltage of the local oscillator sinusoidal waveform, which is then fed through the third capacitor C3 to the combined gates of the second transistor VT2 and the third transistor VT3.

Since the amplification cascade is covered by local consecutive negative feedback on alternating current, its gain is determined by the depth of negative feedback and depends on the resistance of the third resistor R3 and the differential resistance of the open channel of the second field-effect transistor VT2 and the open channel of the third field-effect transistor VT3.

When a sinusoidal local oscillator voltage is received at input 2, the differential resistance Rdif of the second transistor VT2 and the third transistor VT3 changes from 1 / SVT2, VT3 (at the peaks of the sinusoid) to an infinitely large value (in the locked state), where SVT2, VT3 is the differential slope of the open channels field effect transistors VT2, VT3.

At the opening voltage level of the local oscillator signal (at the peaks of the sinusoid), Rdif≪R3, the gain of the gain stage is determined by the following ratio: K≈Rn / Rdif.

When the second transistor VT2 and the third transistor VT3 are locked, the gain of the gain stage on the first transistor VT1 is determined by the following relation: K = Rн / К3, where

R _n - equivalent load resistance, determined by the inductance of the coil L1, the capacity of the fourth capacitor C4 and the load resistance connected to the output of the frequency mixer.

Considering that the second transistor VT2 and the third transistor VT3 are heterogeneous and connected in parallel, the differential resistance of the total conductivity of the channels changes twice during the heterodyne voltage period, the gain of the gain channel K changes from the minimum value, defined as K = Rн / R3 to the maximum value , defined as K = RL / R _diff, twice per period of the heterodyne voltage is a periodic function of time, determined by a voltage oscillator, and may be presented in following m the form:

K (t) = Ko + K ₁ cos (2ω _gt ) + K ₂ cos (4ω _gt ) + ...

where: Ko is the transmission coefficient module at the input signal frequency,

K ₁ , K ₂ ... is the transmission coefficient modulus at the corresponding frequencies that are multiples of the even frequencies of the local oscillator.

Upon receipt of the signal voltage at the input of the frequency mixer, determined by the formula: Uc (t) = Umc cos (ωct), where:

Umc is the amplitude of the input signal,

ωс - circular frequency of the input signal,

on the equivalent load resistance R _n the following components appear:

Uout (t) = Umc cos (ωct) K (t) = Umc cos (ωct) (K ₀ + K _1cos (2ωгt) + K _2cos (4ωгt) + ...) = Umc cos (ωct) K ₀ + Umc cos (ωct) K _1cos (2ωгt) + U _mc cos (ωct) K _2cos (4ωгt) + ... =

where ωg is the circular frequency of the local oscillator.

In the spectrum of the output signal there are frequencies of the form: ωпч = ± 2nωг ± mωс (where n and m are positive integers), which are distinguished by a parallel oscillatory circuit formed by an inductor L1 and a fourth capacitor C4.

A high degree of isolation between the input voltage and the local oscillator voltage circuits is ensured by eliminating the possibility of a current flowing with the local oscillator frequency in the amplification cascades, the low input resistance of the amplification cascade on the side of the second transistor VT2 and the third transistor VT3, and the small gate-drain passage capacity of the second transistor VT2 and the third transistor VT3.

Claims (1)

A frequency mixer containing two field effect transistors, the sources and drains of which are interconnected, characterized in that the first, second, third, fourth, fifth, sixth capacitors are introduced into it, the first, second, third, fourth resistors, the inductor, the first a transistor, a DC power source, the second and third field-effect transistors of different types and connected in parallel, with the first output of the first capacitor, the first output of the first resistor, the first output of the fourth capacitor and the first output of the coil inductors are interconnected and connected to the positive terminal of the DC power source, the second terminal of the first capacitor, the second terminal of the second resistor, the second terminal of the third resistor, the combined sources of the second and third transistors, the second terminal of the fourth resistor are connected to each other and connected to the negative terminal of the power source DC connected to the housing, the second terminal of the second capacitor is connected to the second terminal of the first resistor, the first terminal of the second resistor and the base the first transistor, the collector of which is connected to the second terminal of the fourth capacitor and the second terminal of the inductor connected to the first terminal of the fifth capacitor, the second terminal of which is the output of the intermediate frequency signal, the emitter of the first transistor is connected to the connection point of the first terminal of the third resistor and the first terminal of the sixth capacitor, the second output of which is connected to the combined drains of the second and third transistors, the combined gates of which are connected to the first output of the fourth a resistor and a second terminal of the third capacitor, a first terminal which is the input voltage LO and the first terminal of the second capacitor is the input signal voltage.