JPH0318762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to an oscillator with a frequency of microwave or higher using a transistor or a field effect transistor.

[Description of prior art]

High frequency oscillators using bipolar transistors with a common collector or field effect transistors with a common drain are widely used. FIG. 1 is a typical circuit diagram. That is, the collector electrode is attached to the ground potential, and an inductive impedance L is placed between the base electrode and the ground potential.
By connecting and applying an appropriate bias voltage, the interelectrode capacitance Cbe between the emitter and base acts as a feedback coupling capacitance and an oscillator can be constructed. In this figure, the description of the bias voltage supply circuit is omitted.

In such a high-frequency oscillator circuit, there is an inter-electrode capacitance Cce between the collector and base of the transistor, which exists mainly due to its mechanical structure, so at frequencies where the impedance due to this inter-electrode capacitance Cce is dominant, the apparent The gain of the oscillator decreases, making it impossible to operate as an oscillator.

To operate such an oscillator at higher frequencies, expensive transistors with gain up to higher frequencies must be used. In particular, high-frequency transistors are difficult to obtain and are expensive as power transistors with large output power.

[Purpose of the invention]

The present invention aims to provide a high frequency oscillator that operates at high frequencies using inexpensive and readily available transistors or field effect transistors designed to operate at relatively low frequencies.

[Features of the invention]

The present invention provides an inductive capacitance between the emitter electrode (bipolar transistor) or source electrode (field effect transistor) and ground in that frequency range, and the collector-emitter interelectrode capacitance Cce or the drain-source capacitance Cce. It is characterized by connecting a distributed constant circuit that can cancel the interelectrode capacitance Cdc.

[Explanation based on examples]

FIG. 2 is a circuit diagram of an oscillator according to an embodiment of the present invention.
This oscillator uses a transistor Q, whose collector electrode is connected to ground potential, and whose base electrode is connected to an inductive impedance L. With this configuration,
The emitter and base of this transistor are feedback-coupled via an interelectrode capacitance Cbe, and operate as an oscillator. Also in this figure, the description of the bias circuit is omitted.

The feature of the present invention is that a distributed constant circuit S is connected between the emitter electrode and the ground potential. The distributed constant circuit S is, for example, a strip line with an open end provided on a substrate on which a transistor Q is mounted, and its length l is the oscillation frequency of this oscillator, and the length l is set so that the impedance exhibited at the emitter electrode becomes inductive. be adjusted. The absolute value of this impedance is configured to approximate the absolute value of the impedance that the interelectrode capacitance Cce between the collector and emitter of this transistor Q exhibits at the oscillation frequency.

The equivalent circuit of this oscillator is shown in FIG.
In other words, the distributed constant circuit S acts as an inductance Ls at this oscillation frequency, and the transistor Q
This capacitance is connected in parallel with the interelectrode capacitance Cce of
It acts to offset the influence of Cce. Therefore, even if a transistor is used at low frequencies where the inter-electrode capacitance Cce is relatively large, the effect of this inter-electrode capacitance Cce can be reduced, so the transistor can be used as an oscillator transistor in the high frequency range. It can be used as.

FIG. 4 is a circuit diagram of an embodiment of the present invention. This example uses a field effect transistor F. By connecting the drain electrode to the ground potential, connecting an inductive impedance L between the gate electrode and the ground potential, and applying a bias voltage as shown in the figure, feedback coupling due to the interelectrode capacitance between the gate and source can be achieved. operates as an oscillator. In this circuit, a distributed constant circuit S is connected between the source electrode and the ground potential, and by adjusting its length l, the source electrode exhibits inductive impedance. This inductive impedance acts to cancel the interelectrode capacitance between the drain and source.

FIG. 5 shows the results of measuring the reflection S parameter _S11 from the terminal T connected to the gate electrode using the circuit shown in FIG. In Figure 5, the solid line is the distributed constant circuit S
When connected, the broken line is the measured value in the same circuit when the distributed constant circuit S is disconnected. It can be seen that when the distributed constant circuit S is not connected, this circuit exhibits negative impedance up to about 11 GHz, but when the distributed constant circuit S is connected, it exhibits negative impedance up to about 12.5 GHz. That is, by connecting the distributed constant circuit S, this circuit can be used as an oscillator up to about 12.5 GHz.

FIG. 6 is a diagram showing the surface pattern form of the example circuit whose equivalent circuit diagram is shown in FIG. 4. This circuit is formed on the surface of a ceramic substrate. A metal film is formed over the entire back surface, and the metal film is connected to ground potential. The field effect transistor F has a structure in which the outer case is connected to the drain electrode, and the outer case is connected to the ground potential on the back surface through a through hole provided in the ceramic substrate. A bias voltage is supplied to the source electrode terminal S of this field effect transistor F, and it is connected to the distributed constant circuit S described above. This distributed constant circuit S is constituted by a strip line with a ceramic substrate interposed as a dielectric between it and a metal film at ground potential on the back surface. This distributed constant circuit S is bent into an L-shape with an open end due to the area constraints of the substrate. This distributed constant circuit S is formed such that its length is inductive at the utilized frequency at the source electrode terminal of the field effect transistor F.

The gate terminal G of the field effect transistor F is connected to another distributed constant circuit G, and this distributed constant circuit G
is coupled to the dielectric resonator P. The distributed constant circuit G and dielectric resonator P are coupled spatially without metal contact. The circuit in which the distributed constant circuit G and the dielectric resonator P are connected, as viewed from the point where the gate terminal of the field effect transistor F is connected, is set to be equivalently inductive at the above-mentioned usage frequency. The output circuit of this oscillator is spatially coupled to the dielectric resonator P.

The measurement terminal T described above is temporarily connected between the gate electrode G of the field effect transistor F and the ground electrode by a coaxial terminal as shown in the figure.

Now, to explain the operation of this circuit as an oscillator, FIG. 7 is a basic circuit diagram of a Colpitts type oscillator using field effect transistors. Corresponding to the circuit of the present invention shown in Fig. 4, the capacitor
C ₁ is the electrode capacitance C _GS between the gate and source of the field effect transistor, and the capacitor C ₂ is also the electrode capacitance C _DS between the drain and source. In the present invention, this capacitance C _DS is large relative to the operating frequency, so in order to equivalently reduce it, a distributed constant line is connected in parallel between the drain and source, and this distributed constant line is inductively connected at the operating frequency. By canceling out the capacitance C _DS described above, the capacitance value is set to be substantially small and oscillation is possible at a desired high frequency.

In the above description, a strip line is used as the distributed constant circuit, but the present invention can be implemented using a coaxial line, a waveguide, or any other distributed constant circuit. In addition, although this distributed constant circuit was shown as an example with an open end, the Q
The present invention can be implemented in the same way even if the value of is adjusted. In this case, it is preferable to insert a capacitor in series with sufficiently low impedance at the operating frequency so that the DC voltage is not short-circuited at the tip.

〔Effect of the invention〕

As explained above, according to the present invention, a transistor or a field effect transistor can be used as an oscillator up to a high frequency by connecting an extremely simple circuit. As the frequency of use of microwave transistors or microwave field effect transistors increases, the price thereof increases rapidly and the number of types that can be obtained rapidly decreases. This is especially noticeable in high power transistors. Therefore, the present invention is particularly effective when applied to a high power oscillator.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional oscillator. FIG. 2 is a circuit diagram of an oscillator according to an embodiment of the present invention. Figure 3 is its equivalent circuit diagram. FIG. 4 is a circuit diagram of an oscillator according to an embodiment of the present invention. Fifth
The figure shows the measurement results. FIG. 6 is a diagram showing the form of a circuit pattern surface of an oscillator according to an embodiment of the present invention. FIG. 7 is an equivalent circuit diagram of a Colpitts type oscillator.

Claims (1)

[Claims] 1. A transistor having a collector electrode connected to a ground potential, and an inductive impedance connected between a base electrode of the transistor and the ground potential, and an inductive impedance between the emitter and the base of the transistor. In a high frequency oscillator configured to provide feedback coupling between its emitter and base using interelectrode capacitance, exhibiting inductive impedance at the emitter electrode between the emitter electrode of the transistor and ground potential, A distributed constant circuit is connected in which the absolute value of the impedance approximates the absolute value of the impedance value due to the parasitic capacitance between the collector and emitter electrodes of the transistor itself at the oscillation frequency, cancels out the parasitic capacitance, and reduces the parasitic capacitance to a small value. A high frequency oscillator characterized by: 2 A field-effect transistor having a drain electrode connected to a ground potential, and an inductive impedance connected between the gate electrode of the field-effect transistor and the ground potential, and between the electrodes between the source and gate of the transistor. In a high-frequency oscillator configured to provide feedback coupling between its source and gate using capacitance, an inductive impedance is present at the source electrode between the source electrode of the transistor and the ground potential, and the impedance A distributed constant circuit whose absolute value approximates the absolute value of the impedance value due to the parasitic capacitance between the drain and source electrodes of the field effect transistor at the oscillation frequency, cancels out the parasitic capacitance, and reduces the parasitic capacitance to a small value is connected. A high frequency oscillator characterized by: