JPS5927485B2 - transistor oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor oscillation device used in the field of microwave communications.

Recent transistors have improved their output performance, and can now be used in transistor oscillation devices to obtain an oscillation output of 1 to 10 W in the UHF band.

Such an oscillator is effectively used, for example, as a source oscillator for a local oscillator for transmission in a microwave communication device.

However, increasing the oscillation frequency of a transistor necessarily requires lowering the breakdown voltage of the transistor used, and generally as a high frequency, high output transistor, the breakdown voltage between each electrode becomes a problem.

One of them is the problem of emitter-base breakdown voltage.

Due to the nature of the oscillator, transistor oscillators always have a class A bias applied to the transistors used, but during oscillation, DC feedback is applied due to the collector-emitter current and emitter resistance, and the emitter-base DC bias potential increases as the oscillation output power increases. Along with this, students move from A class to B class to C class.

That is, the emitter-base DC bias voltage changes from forward bias to reverse bias.

Then, an AC amplitude is applied around this DC bias point, but if the DC bias point is already in the reverse breakdown voltage part between the emitter and the base, there is no margin for the AC amplitude and a part of the AC amplitude may break down. cause.

In a transistor oscillator, when a phenomenon like this occurs, it causes the oscillation power to decrease over time and the oscillation frequency to change over time.

An object of the present invention is to eliminate the above-mentioned drawbacks by limiting the deviation of the DC bias voltage between the emitter and base in the direction of reverse bias by an appropriate DC bias voltage value. It is an object of the present invention to provide a transistor oscillation device with stable operation that can prevent voltage breakdown.

According to the present invention, the base voltage of the transistor is set at the voltage dividing point of the series voltage dividing circuit consisting of the first resistor means connected to one end of the power supply in common with the collector, and the second resistor means connected to the other end of the power supply. In the transistor oscillator device, the transistor oscillation device has a DC bias circuit configured such that the emitter-collector current is applied through the emitter and the other end of the power supply through a third series resistor connected between the emitter and the other end of the power supply. A first diode is connected in the direction in which the voltage dividing current flows between the second resistance means and the base voltage application point, and a connection point between the emitter side of the transistor and the third series resistor;
A transistor oscillation device is obtained, characterized in that a second diode is connected in a direction opposite to that of the first diode between a connection point between the second resistance means of the voltage dividing circuit and the first diode. It will be done.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a transistor oscillation device having a conventional DC bias circuit.

The transistor 1 constitutes a Colpitts type oscillation circuit with a feedback circuit whose oscillation frequency is determined by a capacitor 23 and a coil 4.

A DC bias for transistor 1 is applied through choke coils 5 and 6.

Capacitors 7 and 8 are bypass capacitors.

The DC base voltage of transistor 1 is connected to resistor 10 from power supply 9.
The collector-emitter current is determined by the resistor 12.

The oscillation output power is extracted from the output terminal 14 by coupling the coil 4 to the coil 13.

If oscillation does not start, the emitter-base DC bias voltage is naturally biased in the forward direction.

However, as oscillation starts and the output power increases, the collector emitter current increases, so the voltage drop across the resistor 12 increases, that is, DC feedback is applied.

However, since the voltage applied to the base is constant, the emitter-base DC bias voltage shifts from the forward bias at the start of oscillation toward the reverse bias as the oscillation output power increases.

For this reason, voltage breakdown between the emitter and the base occurs for the reasons described below.

FIG. 2 is a diagram showing the emitter-base characteristics and operating point of the transistor 1.

Curve 15 is the emitter-base characteristic; the right side of 0■ is the forward biased portion, the left side is the reverse biased portion, and its breakdown voltage is vb.

As explained above, when oscillation starts and the output voltage increases, the emitter-base DC bias voltage Vo gradually shifts to the reverse bias.

When this Vo becomes a value as shown in FIG. 2, for example, this emitter-base DC bias voltage Vo is filtered and an AC amplitude 16 is applied, and the emitter・Pressure breakdown will occur between the bases.

This phenomenon is illustrated in actual operating characteristics as shown in FIG.

The vertical axis of the curve 17 represents the emitter-base DC bias voltage, with the plus side being the forward bias and the minus side being the reverse bias.

Similarly, a curve 18 shows the base DC current on the vertical axis, with the positive side being the forward direction and the negative side being the reverse direction.

As the power supply voltage increases on the horizontal axis, the base DC current increases, and the emitter-base DC bias voltage shifts toward reverse bias.

If the value exceeds 11V, breakdown voltage will occur between the emitter and base, and the DC bias voltage between the emitter and base will be approximately
At the same time as reaching a constant value, the base DC current begins to decrease due to breakdown voltage current, and finally becomes a current only in the reverse direction.

In this manner, by checking the linearity of the base DC current with respect to the power supply voltage, it is possible to confirm the state of breakdown voltage between the emitter and the base.

As a result, in an oscillator with characteristics as shown in FIG.
If used in (2), the oscillation output power will decrease over time and the oscillation frequency will change over time, making it unusable.

FIG. 4 is a circuit diagram showing an embodiment of a transistor oscillation device having a DC bias circuit according to the present invention.

Portions corresponding to those in FIG. 1 are designated by the same numbers.

A diode 19 is inserted in series with the resistor 10 that applies the base voltage in the conventional embodiment, and its forward voltage drop causes a constant voltage drop from the base voltage of the transistor 1 in the same direction as the emitter-base forward direction and independent of the power supply voltage. Create a point a where a voltage drop can be obtained.

A diode 20 is connected between the emitter of the transistor 1 and this point a.

The diode 20 is connected so that the forward direction seen in the diode characteristics between the emitter and base of the transistor 1 is opposite to the forward direction seen in parallel.

Therefore, diode 20 is connected to the emitter of transistor 1.
As long as base-to-base is forward biased, the cut
Since it is off, the first
It is biased as shown in the figure.

However, the oscillation output power increases and the emitter current increases,
When the emitter-base DC bias voltage of transistor 1 exceeds the reverse biased value, diode 20 becomes forward biased, and the voltage drops across diodes 19 and 20 are constant almost regardless of the current and voltage. The DC bias voltage between the emitter and base of is kept constant.

If this emitter-base DC bias voltage value is fixed to the forward direction side from the DC bias voltage value at which breakdown voltage starts as explained in Fig. 2, the AC amplitude between the emitter and base of transistor 1 It is possible to prevent pressure breakdown.

FIG. 5 shows an example of the operating characteristics of a rerange resistor oscillation device to which a DC bias circuit according to the present invention is added under the same conditions as in FIG. 3.

A curve 21 shows the emitter-base DC bias voltage, and a curve 22 shows the base DC current.

Now, as we increase the power supply voltage on the horizontal axis, the emitter-base DC bias! The pressure shifts in the opposite direction, but the fourth
The voltage is fixed at approximately -0.3V by the diodes 19 and 20 shown in the figure, and does not exceed much as shown in FIG.

Therefore, voltage breakdown does not occur, and the base DC current has sufficient linearity with respect to the power supply voltage as shown by curve 22.
Even if the specified power supply voltage of this oscillator is -18V or higher, the emitter
It can be seen that no pressure breakdown occurred between the bases.

As explained above, in the DC bias circuit of the transistor that causes oscillation, the
Create a voltage drop point that is in the same direction as the forward direction of the base and where a constant voltage independent of the power supply voltage is obtained, and connect the emitter of the transistor to this point.
By connecting diodes in parallel and opposite to the forward direction of the diode characteristics between the bases, the DC bias voltage between the emitter and base of the transistor is fixed at an appropriate value, and the AC voltage between the emitter and base of the transistor is fixed. Breakdown of breakdown voltage due to vibration amplitude is prevented, and a transistor oscillation device with stable operation can therefore be obtained.

In the embodiment shown in FIG. 4, only one diode 19 and one diode 20 are inserted, but a plurality of diodes may be connected and inserted in series.

For example, if two diodes 19 are connected in series instead of using one diode 19, the emitter-base DC bias voltage of the operating characteristics shown in FIG. It can be fixed at approximately +0.4■.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example of a transistor oscillation device having a DC bias circuit, Fig. 2 is a diagram for explaining breakdown voltage breakdown between the emitter and base of the transistor in the circuit of Fig. 1, and Fig. 3 1 is a diagram showing the operating characteristics of the transistor oscillation device shown in FIG. 1, FIG. 4 is a circuit diagram showing an embodiment of the transistor oscillation device having a DC bias circuit according to the present invention, and FIG. 5 is a diagram showing the transistor oscillation device shown in FIG. FIG. 1: Transistor, 2 and 3: Capacitor, 4: Coil,
5 and 6: choke coil, 7 and 8: bypass capacitor,
9: Power supply, 10 and 11: Resistor, 12: Resistor, 19 and 20
:diode.

Claims (1)

[Claims] 1. The base voltage of the transistor is connected to the first capacitor at the voltage dividing point of the series voltage dividing circuit consisting of the first resistor means connected in common with the collector to one end of the power supply and the second resistor means connected to the other end of the power supply. A third resistor means is connected to the base electrode of the transistor through a first choke coil, and the other end of the third resistor means is connected to the base electrode of the transistor through a first choke coil. a DC bias circuit that is grounded and connected to the emitter electrode of the transistor via a second choke coil to flow an emitter-collector current;
The collector electrode and the emitter electrode are connected by a third capacitor, the base electrode and the emitter electrode are connected by a fourth capacitor, and the third and fourth capacitors are connected between the base electrode and the collector electrode. In the transistor oscillator device, the transistor oscillation device also has a feedback circuit connected to a coil that determines the oscillation frequency, and a first resistor is provided between the connection point of the first resistance means and the first choke coil and the second resistance means. diodes are connected in the direction in which the voltage dividing current flows, the third resistance means and the second choke coil are connected, and the cathode electrode of the second diode is connected between the cathode electrode of the first diode and the third resistance means and the second choke coil. A transistor oscillation device, characterized in that the transistor is connected so as to be on the side of the first diode.