JPS5826702B2 - self-excited mixing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-excited mixing circuit used in high frequency circuits such as FM radio receivers and television receivers.

A self-excited mixing circuit that performs local oscillation function and frequency conversion function with one active element has one active element compared to a separately excited mixing circuit.
The circuit configuration is simple because the elements can be removed.

However, this is technically difficult because the injection amount of the local oscillation signal, the stability of oscillation, and the bias point of the active element that determines the conversion gain vary depending on the characteristics.

Currently, a self-excited mixing circuit using bipolar transistors has been developed, but this has poor cross-modulation characteristics and needs to be improved.

An object of the present invention is to provide a self-excited mixing circuit with excellent cross-modulation characteristics.

The present invention improves the cross-modulation characteristics by using a dual-gauge FET (field effect transistor) as an active element, and also by separating the RF (high frequency signal) input section and the local oscillation signal feedback circuit. To realize a self-excited mixing circuit suitable for high frequency circuits such as FM receivers and television receivers by eliminating mutual adverse effects.

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

The figure shows a self-excited mixing circuit according to the invention.

First, the DC system will be explained.

In the figure, 2 indicates a dual gate FET, and 2a to
2d indicates a drain electrode, a source electrode, a first gate electrode, and a second gate electrode, respectively.

The source electrode 2b of the FET 2 is grounded.

1a is a DC bias power supply for the second gate electrode 2d, which is applied via a resistor 6a.

1b is a DC bias power supply for the first gate electrode 2c, and is applied through a resistor 6b.

1c is a DC power supply for the drain electrode 2a, which is applied via the choke coil 4b and the coil 4a.

Next, the high frequency system will be explained.

An RF (high frequency) signal is input from the terminal 7a to the first gate electrode 2c via the coupling capacitor 3a.

A capacitive element 5C is connected between the drain electrode 2a and the ground at the oscillation frequency.

Moreover, between the drain electrode 2a and the second gate electrode 2d,
An inductive circuit 5b is connected at the oscillation frequency.

Further, a capacitive circuit 5a at the oscillation frequency is connected between the second gate electrode 2d and the ground.

The circuits 53 to 5c described above are feedback circuits that determine the oscillation frequency.

Further, a coil 4a and a capacitor 3 are connected to the drain electrode 2a.
An IF tuning circuit consisting of the coil 4a and the capacitor 3b is connected, and an IF signal is taken out from the connection point between the coil 4a and the capacitor 3b via the capacitor 3C.

Next, the circuit operation will be explained.

When an RF signal is input to the terminal 7a, the feedback circuits 5a and 15b are connected to the drain electrode 2a and the second gate electrode 2d.
The local oscillation signal generated by 15c and the RF signal are mixed, and the difference component, that is, the IF signal is selected by the IF tuning circuit connected to the drain electrode 2a,
An IF signal is output to terminal 7b.

The present invention is particularly characterized in that a dual gate FET with good cross-modulation characteristics is used as an active element, and that the RF signal input and the local oscillation feedback circuit are separated.

That is, by using the dual gate FET, it is possible to obtain better cross-modulation characteristics than a self-excited mixing circuit using bipolar transistors.

In addition, all the feedback circuits are connected to the drain electrode and the second gate electrode, and are separated from the RF signal input section.
Matching of inputs becomes easy, and the oscillation circuit can be made less susceptible to adverse effects from the inputs, so good mixing characteristics can be obtained.

As described above, according to the present invention, the dual gate FET
By using a oscillator, the cross-modulation characteristics are improved, and the circuit configuration has good separation between input and output, making input matching easier. Also, the oscillation circuit is less susceptible to negative effects from the input, resulting in good characteristics. A promising self-excited mixing circuit is obtained.

[Brief explanation of drawings]

The figure is a circuit diagram showing an embodiment of a self-excited mixing circuit using dual gate FETs according to the present invention. 1a to 1C: DC power supply, 2: Dual gate FBT, 2
a: drain electrode, 2b: source electrode, 2C: first gate electrode, 2d: second gate electrode, 38-3c: capacitor, 4a-4b: coil, 5a-5C: feedback circuit, 6
a to 6b: bias resistance.

Claims (1)

[Claims] 1 A self-excited mixing circuit using a dual gate FET, in which the source electrode is grounded, an RF signal is input to the first gate electrode, and an inductive feedback circuit at the oscillation frequency is provided between the drain electrode and the second gate electrode. is connected, a capacitive feedback circuit is connected between the drain electrode and the source electrode, a capacitive feedback circuit is connected between the second gate electrode and the source electrode, and an IF frequency signal is extracted from the drain electrode. A self-excited mixing circuit.