JPS6044842B2 - FET self-oscillation mixing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-oscillating mixing circuit using dual gate FETs.

In conventional self-oscillation mixing circuits such as television tuners and radio tuners, bipolar transistors are used as active elements, and due to the nonlinearity of the elements, performance against cross-modulation interference and internal modulation interference is insufficient. There were some drawbacks that were not achieved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a self-oscillating mixing circuit which eliminates the above-mentioned drawbacks of the prior art and improves performance against various disturbance characteristics.

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 a lower signal output terminal,
3 is a dual gate FET whose source 12 is grounded;
0 is the first gate, 11 is the second gate, and 13 is the drain.

6, 9, and 714 are capacitors, 4 is a capacitive impedance element, 5 is an inductive impedance element, 7 is a capacitive impedance element, and 8 is a positive 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 1, 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, the capacitive impedance elements 4 and 7, the inductive impedance element 5, the capacitor 14, the drain impedance of the FET, and the second gate impedance. This oscillation signal and the signal input from the high-frequency signal input terminal 1 are mixed and amplified by the FET, and then passed through a π-shaped IF tuning circuit consisting of the drain impedance of the drain 13 to the capacitor 14, the inductor 8, and the capacitor 9, and then sent as an IF signal to the lower signal. It is output from output terminal 2. The capacitor 6 has the function of improving the impedance separation between the IF frequency band and the local frequency band to ensure oscillation, mixing, and amplification operations.
If the frequency difference between the frequency band and the oscillation frequency band is small, a relatively small capacitance value is required.

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. In addition, when it is necessary to make the oscillation frequency variable as in a television tuner, the inductance of the inductive impedance element 5 or the capacitance of the capacitive impedance element 7 may be made variable.
FIG. 2 shows a second embodiment of the present invention, in which the capacitive impedance element 4 of the first embodiment is constructed with a capacitor 17, and the capacitive impedance element 7 is constructed with a variable capacitance diode 15 to make the oscillation frequency variable. It is.

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, 1
1 is the second gate, and 13 is the drain. 8 is an IF tuning coil.

6, 9, 14, 16, 17 and 28 are capacitors.

15 is a variable capacitance diode, and 18 is a resonant coil.

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.
Bias is supplied by 2, respectively. Further, a voltage is supplied to the drain 13 via the choke coil 27 and the IF tuning coil 8. FET3 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 make the capacitance variable. In addition, 29,30
, 31 are bypass capacitors. In this example, the inductive impedance element 5 of the first embodiment is replaced with a resonant inductor 18, the capacitive impedance element 4 is replaced with a capacitor 17, and the capacitive impedance element 7 is used for DC blocking or oscillation frequency. Capacitor 1 that controls the variable range of
3 and a variable capacitance element group consisting of a variable capacitance diode 15. The oscillation frequency is changed by the voltage applied to the variable capacitance diode 15, and the oscillation frequency is changed by the voltage applied to the variable capacitance diode 15. On the other hand, a lower signal of a constant frequency is taken out from the IF signal output terminal 2.

FIG. 3 shows a third embodiment of the present invention, in which the inductive impedance element 5 of the first embodiment is replaced with a parallel resonant circuit of a group of variable capacitance elements consisting of a resonant inductor 18, a capacitor 16, and a variable capacitance diode 15. It is.

In the figure, 32 is an inductance, 33 is a bypass capacitor, and 34 is a capacitor. In this example, a capacitor 34 is used as the capacitive impedance element 7,
A capacitor 17 is used as the capacitive impedance element 4 to change the capacitance of a variable capacitance diode 15 connected in parallel with a resonant inductor 18, thereby changing the equivalent inductance of the parallel resonant circuit and changing the oscillation frequency. The inductor 32 is for direct-currently grounding the variable capacitance diode I5. FIG. 4 shows a fourth embodiment of the present invention.

In this example, a series resonant circuit consisting of a resonant inductor 1L and a variable capacitance diode 15 is used as the inductive impedance element of the first embodiment, and the voltage applied to the variable capacitance diode 15 from the terminal 20 via the resistor 26 is varied. The capacitance value of the variable capacitance diode 15 is changed to change the equivalent inductance of the series resonant circuit, thereby changing the oscillation frequency. In this example, the capacitor 34 is used as the capacitive impedance element 7 of the first embodiment, and the capacitor 17 is used as the capacitive impedance element 4. As explained above, by employing the self-oscillation mixing circuit of the present invention in a television tuner and a radio tuner, performance against cross-modulation interference and internal modulation interference caused by third-order or higher-order nonlinearity is improved.

In particular, in a positive tuner, the video carrier frequency, audio carrier frequency, and local oscillation frequency of the 6 channels of the American channel cause color heat due to the above-mentioned nonlinearity.
It is effective against channel color heat disturbance and 4-channel color heat disturbance in which the audio carrier frequency and local oscillation frequency of the 4 channels of the European channel cause color heat due to the above-mentioned non-linearity.

[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. FIGS. 2, 3, and 4 are specific circuit diagrams of the circuit shown in FIG. 1. 1...High frequency signal input terminal, 2...
...IF signal output terminal, 3...dual gate FET
l4... Capacitive impedance element, 5... Inductive impedance element, 6... Capacitor, 7... Capacitive impedance element, 8... IF tuning inductor, 9... Capacitor, 10. ...1st gate, 11
...Second gate, 12...Source, 13...Drain, 14...Capacitor, 15...Variable capacitance diode, 16...Capacitor, 17...Capacitor, 18...Resonance Inductor, 21-26...resistance,
29-31, 33... Bypass capacitor, 32...
・Inductor, 34... Capacitor.

Claims (1)

[Claims] 1. A dual-gate FET whose source electrode is grounded and has first and second gates, a capacitor connected to the drain electrode of this FET, and a connection between the other end of this capacitor and the ground. an inductive impedance element connected between the other end of the capacitor and the second gate of the FET, and a second capacitive impedance element connected between the second gate of the FET and ground. An oscillation circuit is constituted by the capacitive impedance element, and the first
A FET self-oscillation mixing circuit characterized in that a high frequency signal is input to the gate and an IF signal is output from the drain electrode of the FET. 2. The FET self-oscillation mixing circuit according to claim 1, wherein a variable capacitance element is used as the first capacitive impedance element. 3. The FET self-oscillation mixing circuit according to claim 1, wherein a variable inductance element is used as the inductive impedance element. 4. The FET self-oscillating mixing circuit according to claim 1, wherein the conductive impedance element is constituted by an element group consisting of an inductor and a variable capacitance element connected in parallel to the inductor. 5. The FET self-oscillating mixing circuit according to claim 1, wherein the inductive impedance element is constituted by an element group consisting of an inductor and a variable capacitance element connected in series with the inductor.