JPS6134741Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to improvement of a microwave oscillation circuit. Specifically, it relates to improvements made with the aim of improving the stability of the oscillation frequency in microwave oscillation circuits using field effect transistors (FETs) made using gallium arsenide (GaAs) as a material. It is.

GaAsFET is currently the only transistor that can be used in the microwave band, and is also used as an oscillation element. FIG. 1 is an example of a GaAsFET oscillation circuit. This circuit is composed of microstrip lines formed on a ceramic substrate 1, and the entire back surface (not shown) of the substrate is metallized. The surface of the board has a metal pattern as shown in the figure to form a circuit. 2 is a GaAsFET, which is a high frequency transistor having three electrodes: gate G, drain D, and source S. A transmission line is connected to each electrode. The gate side line 3 and the drain side line 4 are arranged at right angles, and a dielectric resonator 6 is arranged at the corner thereof, so that feedback is applied from the drain to the gate to cause oscillation. The output is taken out from the source side line 5. Since the source output impedance is low, a low impedance line is connected to the source terminal of the FET, and the output impedance of the oscillator is converted to high impedance using a tapered transformer as shown in the figure. 7 is a DC cut capacitor for DC isolation between the load and the oscillator.

On the other hand, the gate side line 3 is terminated with a resistor 8 having a line characteristic impedance (for example, 50Ω). The other end of the resistor 8 is connected to the back surface of the substrate through a through hole 9. This resistor 8 is effective in suppressing sparse oscillation and mode jump.
This is essential to obtain stable oscillation.

Reference numerals 10 and 11 surrounded by dotted lines in the figure are filters for bias circuits, which are connected to the source and drain, respectively. These circuits form a high-frequency rejection filter and prevent microwaves from leaking into the bias circuit. The circuit in Figure 1 has a bias circuit configured to operate with a single power supply, and when a positive voltage is applied to the bias terminal 12, current flows from the drain to the source of the FET, then through the resistor 13, and through the through hole. Through 14,
It flows into the back surface of the board, which is the ground plane. The source-gate potential is automatically given by the voltage drop across the resistor 13.

Now, when operating a FET, it is normal to use it with no current flowing through the gate, but when configuring an oscillation circuit as described above, a small amount of current may flow through the gate.
Moreover, the magnitude of the current is affected by the oscillation output, etc. It also changes depending on the temperature. If current flows through the gate and flows through the resistor 8 to the ground plane, the potential between the source and gate changes due to the voltage drop caused by the resistor 8, resulting in an adverse effect that the oscillation frequency is affected. Although this effect is not so large, it cannot be ignored if, for example, frequency stability of about 100 KHz is required for an oscillation frequency of about 10 GHz. Also,
It is difficult to predict the magnitude of the gate current until you actually create an oscillator, connect it to a certain load, and operate it, so it is best to consider the effect of the gate current in advance when designing. Have difficulty.

This invention was made in view of these points,
The object of the present invention is to obtain a microwave oscillation circuit in which gate current does not affect microwave characteristics at all.

In the microwave oscillation circuit according to the present invention, a high impedance line is connected in parallel to the matching termination portion of the gate side transmission line, so that the matching termination is achieved in terms of high frequency, and the circuit is short-circuited in terms of DC.

In the present invention, since the gate current flows through the line connected in parallel to the matching termination, that is, the shorting line, the gate current flows through the matching load as in the conventional case, and the voltage drop caused by the matching load causes the gate current to flow between the source and the gate. The potential can be prevented from changing, and the oscillation frequency will not be adversely affected by the gate current.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
An embodiment of the present invention has a line 15 as shown in FIG.
In this case, the resistor 8 as a matching load is short-circuited. This line 15 has a sufficiently high impedance for microwaves, so that the microwaves flow through the resistor 8, while the DC component flows through the line 15. In other words, high frequency matched termination,
It is a short circuit in terms of DC. Figure 2 shows the equivalent circuit.

Note that the line 15 may be constructed of a strip line, or may be constructed using, for example, a thin conducting wire.

As described above, according to the present invention, in a microwave oscillation circuit having an FET, the terminal part of the gate side transmission line is connected to a matched load and a high impedance line so that the termination part is a matched termination in terms of high frequency and a short circuit in terms of DC. Since the gate current is connected in parallel, the gate current has no effect on the microwave characteristics, and a highly stable oscillator can be manufactured with extremely high reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a configuration of an FET oscillator showing an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of FIG. 1. 1 is a ceramic substrate, 2 is a GaAsFET, 8 is a gate side line, 4 is a drain side line, 5 is a drain side line, 6 is a dielectric resonator, 7 is a capacitor, 8
is a resistor, 9 is a through hole, 10 and 11 are high-growth blocking filters, 12 is a bias terminal, 13 is a resistor,
14 is a through hole, and 15 is a shorting line.

Claims (1)

[Claims for Utility Model Registration] A field effect transistor, a transmission line connected to the gate electrode of the transistor is terminated with a matched load, a transmission line connected to the drain electrode is open terminated, and the gate side transmission A dielectric resonator is arranged at a position sandwiched between the line and the drain-side transmission line so as to be electromagnetically coupled to both lines, and a positive signal is transmitted from the drain to the gate via the dielectric resonator path. In a microwave oscillation circuit in which feedback is applied to generate microwave oscillation and an oscillation output is extracted from a transmission line connected to the source electrode of the transistor, the terminal portion of the transmission line on the gate side is a matched termination in terms of high frequency. , a microwave oscillation circuit characterized in that a high impedance line is connected in parallel to the matching load so as to be short-circuited in terms of direct current.