JPS5947485B2 - FET self-oscillation mixing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a FET self-oscillation mixing circuit that improves IF amplification.

Feedback is applied from the drain to the second gate to cause oscillation, and the first
In a source-grounded dual-gate FET self-oscillating mixing circuit that inputs a high-frequency signal to the gate and extracts the IF frequency from the drain, one way to improve the conversion gain is to use a bipolar transistor mixing circuit to connect the base and emitter (mixing circuit input In the same way as lowering the impedance of the side) in the IF frequency band, it is possible to connect a series resonant circuit that resonates in the IF frequency band between the first gate and the source (earth), but the input impedance of the FET is high. Therefore, there is a drawback that the influence of this series resonant circuit is large in high frequency tuning circuits.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a mixing circuit that increases the IF amplification degree of a dual-gate FET self-oscillating mixing circuit and improves the conversion gain.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the basic configuration of a first embodiment of the present invention, which is made up of various high frequency circuit elements. In the figure, 1 is a high frequency signal input terminal, 2 is an IF signal output terminal, and 3 is a high frequency signal input terminal.
is a dual gate FET with the source 12 grounded, and 10
is the first gate, 11 is the second gate, and 13 is the drain.

6, 9, 14 are capacitors, 5 is an inductive impedance element, 4, 7 is a capacitive impedance element, 8
is an IF tuning inductor, 32 is an inductor, and 33 is a capacitor.

Next, the operation will be explained.

The high frequency voltage generated at the drain 13 is divided by the capacitor 6 and the capacitive impedance element 7, and this is divided by the inductive impedance element 6 and the capacitive impedance element 4.
is fed back to the second gate 11, and oscillates at a resonance frequency determined by the capacitive impedance elements 4 and 6, the capacitive impedance element 7, the inductive impedance element, the capacitor 14, the drain impedance of the FET, and the second gate impedance. do. This oscillation signal and the signal input from high frequency signal input terminal 1 are connected to the FET
mixed and amplified from drain 13 to capacitor 14
, a drain impedance, an inductor 8, and a capacitor 9. The capacitor 6 has the function of improving impedance separation between the F frequency band and the local oscillation frequency band to ensure oscillation, mixing, and amplification operations, and requires a relatively small capacitance value.

The capacitive impedance element 4 connected to the second gate is F
If the second gate of the ET has capacitive impedance, it may not be necessary, but considering uncertain factors such as variations, it is necessary to connect it. The inductor 32 and capacitor 33 constitute a series resonant circuit that resonates in the F frequency band, and the second gate is grounded at high frequency in the F frequency band to increase the degree of amplification in the F frequency band and convert it into a self-oscillating mixed circuit. This improves the gain.

FIG. 2 shows a second embodiment of the present invention, in which the capacitive impedance element 4 of the first embodiment is replaced by a capacitor 17, the capacitive impedance element 7 is replaced by a capacitor 16 and a variable capacitance diode 15, and an inductive impedance element 5 is used. is constructed with a resonant inductor 18, and the oscillation frequency is made variable.

In the figure, 1 is a high frequency signal input terminal, 2 is an IF signal output terminal, 3 is a dual gate FET whose source 12 is grounded by a bypass capacitor 30, 10 is a first gate, 11
is the second gate, and 13 is the drain.

8 is an IF tuning coil.

32 is an inductor, and 33 is a series resonant circuit that resonates in the IF frequency band with a capacitor.

Terminal 19 is a +B voltage supply terminal and resistor 23 is connected to the first gate.
and 24 to resistors 21 and 2 to the second gate.
2 respectively supply a bias via an inductor 32. Further, a voltage is supplied to the drain via the chiyoke coil 27 and the IF tuning coil 8. F
ET is self-biased by source resistor 25. A tuning voltage is applied to the variable capacitance diode 15 from the tuning voltage terminal of the terminal 20 via the resistor 26 to change the capacitance.
Note that 29, 31, and 34 are bypass capacitors.
In this example, the tuning voltage applied to the terminal 20 is changed to change the oscillation frequency, and a signal with a wide range of frequencies input to the high frequency input terminal is converted into an IF signal, which is output from the terminal 2.

A series resonant circuit consisting of inductors 32 and 33 connected to the second gate that resonates in the IF frequency band lowers the impedance of the second gate in the F frequency band and increases the amplification of the F signal. Further, the bias for the second gate is applied from the midpoint of this series resonant circuit. Figure 3 shows the conversion gain on the vertical axis, the channel arrangement of the American channel on the horizontal axis, and the series resonant circuit that resonates in the IF frequency band.
The results of the present invention when the gate is used and the conversion gain when the gate is not used are shown by solid lines and broken lines, respectively.As is clear from this figure, by using a series resonant circuit for the second gate, a gain of 5 to 7 dB is obtained. It is possible to improve conversion gain.

[Brief explanation of drawings]

FIG. 1 shows the basic configuration of a first embodiment of a self-oscillating mixing circuit using dual gate FETs according to the present invention. FIG. 2 shows the second embodiment, and FIG. 3 shows the relationship between conversion gain and channel. 1...High frequency signal input terminal,
2... IF signal output terminal, 3. ．． ．． Dual Gate F
ETl4... Capacitive impedance element, 5... Inductive impedance element, 6... Capacitor, 7...
・Capacitive impedance element, 8...F tuning inductor, 9...capacitor, 10...first gate, 1
1... Second gate, 12... Source, 13... Drain, 14... Capacitor, 15... Town variable diode, 16... Capacitor, 17... Capacitor, 18...・Resonant inductor, 21-26...Resistor, 29-31, 34...Bypass capacitor, 32-
...Inductor, 33...Capacitor.

Claims (1)

[Claims] 1 Connect a capacitor to the drain of the dual gate FET used with source common, connect a capacitive impedance element between the other end of this capacitor and ground, and connect an inductive impedance element between the second gate and the second gate. In a self-oscillation mixing circuit that configures an oscillation circuit by connecting a capacitive impedance element between the second gate and the ground, inputs a high frequency signal to the first gate, and takes out an IF signal from the drain, the second
A FET self-excited mixing circuit characterized by connecting a series resonant circuit that resonates in an IF frequency band between a gate and ground.