JPS5947484B2 - FET self-oscillation mixing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a FET self-oscillating mixing circuit that improves conversion efficiency.

Feedback is applied from the drain to the second gate to cause oscillation, and the first
In a dual-gate FET self-oscillating mixing circuit with a common source that inputs a high-frequency signal to the gate and takes out the IF signal from the drain, one way to improve the conversion efficiency is to use a mixing circuit using bipolar transistors to generate the IF signal.
Similar to improving the conversion gain by lowering the input impedance in the frequency band, one idea is to connect a series resonant circuit that resonates in the IF frequency band between the first gate and the source to lower the impedance on the input side of the mixed circuit. However, FET
Since the input impedance is high, the disadvantage is that it has a large effect on the high frequency tuning circuit connected to the input.

An object of the present invention is to provide a circuit that improves the conversion efficiency of a dual-gate FET self-oscillating mixing circuit by employing a technology different from the conventional technology described above.

The present invention provides a first dual-gate FET self-oscillating mixing circuit.
The gate and the second gate are connected through a capacitor, and the oscillation power generated by applying feedback to the second gate and the drain is injected into the first gate into which a high-frequency signal is input.

An embodiment of the present invention will be explained in detail with reference to the drawings below.

FIG. 1 shows the basic configuration of an 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, 3 is a dual gate FET whose source 12 is grounded, 10 is a first gate, 11 is a second gate, and 13 is a drain.

6, 9, 14, and 15 are respective capacitors, 4 is a capacitive impedance element, 5 is an inductive impedance element, T is a capacitive impedance element, and 8 is an IF tuning inductor.

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 T, and this is divided by the inductive impedance element 5 and the capacitive impedance element 4.
is fed back to the second gate 11, and oscillates at a resonant frequency determined by the capacitor 6, capacitive impedance elements 4 and 7, inductive impedance element 5, capacitor 14, the drain impedance of the FET, and the second gate impedance. . This oscillation signal is injected into the first gate via the capacitor 15, and the signal input from the high-frequency signal input terminal 1 is mixed and amplified by the FET, and the π consisting of the drain 13, capacitor 14, drain impedance, inductor 8, and capacitor 9 is The IF signal is output as an IF signal from the IF signal output terminal 2 via a type IF tuning circuit. The capacitor 6 has the function of improving the impedance separation between the IF frequency band and the local oscillation frequency band to ensure oscillation, mixing, and amplification operations, and is relatively small when the frequency difference between the IF frequency band and the oscillation frequency band is small. Requires capacity. The capacitive impedance element 4 connected to the second gate may be unnecessary if the second gate of the FET has capacitive impedance, but it is necessary to connect it considering uncertain factors such as variations. The feature of the present invention is that a capacitor 15 is connected between the first gate and the second gate, and self-oscillation mixing operation can be performed even without this capacitor. Excitation mixing circuit becomes possible.

Figure 2 shows the capacitive impedance element 4 in Figure 1.
In the FET self-oscillation mixing circuit of an American channel VHF tuner, in which a fixed capacitor is used as a capacitive impedance element, a variable capacitor is used as a capacitive impedance element 7, and an independent inductor is connected as an inductive impedance element 5 for the high band and low band. This shows the effectiveness.

The solid line shows the conversion gain when the first gate and the second gate are connected with a capacitor of 2 to 4 pF, and the broken line shows the conversion gain when no capacitor is connected, and an improvement in the conversion gain of about 1 to 3 dB is observed. As described above, according to the present invention, it is possible to improve the conversion gain with a simple circuit configuration in which only one capacitor is connected to the first gate and the second gate.

[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 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... IF tuning inductor, 9...
・Capacitor, 10...First gate, 11...
・Second gate, 12... Source, 13...
...Drain, 14...Capacitor, 15...
・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 an FET self-oscillation mixing circuit, an oscillation circuit is constructed by connecting a capacitive impedance element between the two gates and the ground, a high frequency signal is input to the first gate, and an IF signal is taken out from the drain. A FET self-oscillation mixing circuit characterized in that a capacitive impedance element is used to connect between the FETs.