JPS6134742Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a bias circuit for FET (field effect transistor). To be more specific,
This paper relates to an improvement of the bias voltage application circuit in a single power supply operated GaAsFET oscillator.

GaAsFET is currently the only transistor that can be used in the microwave band, and is also used as an oscillation element. Figure 1 is an example of a GaAsFET resonant 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: a gate (G), a drain (D), and a source (S). A transmission line is connected to each electrode. Gate side track 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. The source output impedance is low, so 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.

Portions 10 and 11 surrounded by dotted lines in the figure are filters for bias circuits, and 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.
Further, it flows through the resistor 13, passes through the through hole 14, and flows into the back surface of the substrate, which is the ground plane. sauce·
The potential between the gates is automatically given by the voltage drop across the resistor 13.

Further, the line 15 is a gate current bias line for preventing the microwave characteristics of the oscillator from being affected when a gate current flows through the FET.

The equivalent circuit of the conventional FET oscillator described above, focusing on its bias circuit, is shown in FIG.

By the way, when attempting to mass-produce a FET oscillator as shown in FIG. 1, the strip line can be made of a thick film printed circuit, and the resistors 8 and 15 can also be made of printed resistors. Therefore, the manufacturing method is to attach the FET chip to a substrate on which the resistor and circuit are printed, then solder the chip capacitor 7, and finally attach the dielectric resonator.

In this process, the process of attaching the capacitor 7 is
This is a time-consuming process, and it is difficult to obtain capacitors that are inexpensive and have good high-frequency characteristics. Instead of using the capacitor 7, a DC cut (not shown) may be formed using a planar circuit, but this requires pattern precision and is not suitable for mass production. The present invention was developed in view of this point, and is a method for providing direct current isolation between the load and the oscillator.
The purpose of this invention is to obtain a bias circuit for an FET oscillator that does not require a DC cut capacitor and can simplify the manufacturing process.

The bias circuit of the FET oscillator according to the present invention is
A bias resistor is inserted into the transmission line connected to the source electrode of the FET, and the above
The source electrode of the FET is grounded in a direct current manner.

According to the present invention, since the bias resistor is installed in the transmission line that takes out the oscillation output, the transmission line between the load and the oscillator (oscillator output part) is at ground potential, and the DC cut This eliminates the need for a capacitor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 3 shows an embodiment of the present invention, in which a bias resistor 13 is provided in a part of the source side transmission line 5. The other end of this resistor 13 is connected to the microwave output end via a strip line, and is also grounded through a filter 10 and a through hole 14.

Therefore, in this embodiment, the microwave output terminal is at ground potential, and the DC cut capacitor provided in the conventional circuit can be omitted, and the manufacturing process can be significantly simplified. Furthermore, in this embodiment, the oscillator output is connected to the load via the resistor 13 in terms of microwaves, and therefore the stability of the oscillator with respect to external loads is improved.

Although the oscillator output is slightly reduced by the resistor 13, this can be sufficiently compensated for by increasing the source output of the original FET, and does not pose any problem in actual use.

As described above, according to the present invention, in a microwave oscillator using an FET, a resistor is provided in the transmission line connected to the source electrode in order to provide a potential between the source and gate. becomes the ground potential, which eliminates the need for a DC cut capacitor in conventional circuits, which simplifies the manufacturing process and improves stability against loads.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional FET oscillator, FIG. 2 is an equivalent circuit diagram of the bias circuit shown in FIG. 1, and FIG. 3 is a block diagram showing an embodiment of the present invention. 1 is a ceramic substrate, 2 is a GaAsFET, 3 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-frequency blocking filters, 12 is a bias terminal, 13 is a resistor,
14 is a through hole, and 15 is a shorting line.
Note that the same reference numerals in each figure indicate the same or equivalent parts.

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 placed at a position sandwiched between the line and the drain-side transmission line so as to be electromagnetically coupled to both lines, and positive feedback is provided from the drain to the gate via the dielectric resonator. FET that generates microwave oscillation and extracts the oscillation output from the transmission line connected to the source electrode of the transistor.
An FET oscillator, characterized in that a resistor is inserted into the transmission line connected to the source electrode, and the source electrode of the field effect transistor is grounded via the resistor in a DC manner. bias circuit.