JPH06318826A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To protect a field effect transistor(TR) as an amplifier element economically with respect to the amplifier circuit employing two power supplies. CONSTITUTION:The amplifier circuit employs two power supplies, that is, a gate bias power supply 2 used to impress a gate bias voltage to a gate of a field effect TR 1 via a 2nd resistor T and a drain power supply 3 to impress a drain voltage to its drain via a 1st resistor 6. A protection TR 4 whose base receives a voltage difference between the gate bias power supply 2 and the drain power supply 3 and which is closed when the gate bias voltage is impressed to the gate of the field effect TR 1 is connected between the drain power supply 3 and the drain of the field effect TR 1 via the 1st resistor 6. Then a bias adjustment TR 5 is connected between the gate and the drain of the field effect TR 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit using two power supplies, a gate bias power supply and a drain power supply. In the microwave band amplification circuit, for example, a GaAs field effect transistor is often used as an amplification element. When such a field effect transistor is used, two power supplies, a gate bias power supply and a drain power supply, are required. In an amplifier circuit using two power sources, when a drain voltage is applied to the drain of a field effect transistor and a gate bias voltage is not applied to its gate, a large drain current flows, causing deterioration of the field effect transistor. It will burn out. Therefore, it is necessary to suppress the drain current when the gate bias voltage is not applied.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory view of a conventional example, in which 31 is a field effect transistor, 32 is a gate bias power supply, and 33.
Is a drain power supply, 34 is an npn-type protection transistor, 35 is a pnp-type bias adjustment transistor, 3
6, 37 are matching circuits, 38 and 39 are inductances, 4
0 is an input terminal, 41 is an output terminal, and R11 to R15 are resistors.

The field effect transistor 31 is, for example, a GaAs field effect transistor for the microwave band, and shows the case of an n-channel depletion type. At the drain of the field effect transistor 31, for example, V _DD = + 5V
From the drain power supply 33 of the resistor R11 and the inductance 3
9 and a drain voltage is applied to the gate of the field effect transistor 31, and a resistor R12 and an inductance 38 are applied to the gate of the field effect transistor 31 from the gate bias power source 32 of V _GG = -5V, for example.
A gate bias voltage is applied via and the source of the field effect transistor 31 is connected to the ground.

Resistors R13, R14 and R15 are connected between the gate bias power source 32 and the drain power source 33,
The base of the pnp type bias adjusting transistor 35 is connected to the connection point of the resistors R13 and R14, and the emitter thereof is connected to the connection point of the resistor R11 and the inductance 39.
The collector is connected to the connection point between the resistor R12 and the inductance 38, and the fact that the emitter potential changes according to the drain current is used to automatically adjust the gate bias voltage of the field effect transistor 31 to an optimum value. .

The base of the npn type protection transistor 34 is connected to the connection point of the resistors R14 and R15, the emitter thereof is connected to the ground, and the collector thereof is connected to the emitter of the bias adjusting transistor 35. Also resistors R11-R
The value of 15 is, for example, R11 = 180Ω, R12 = 10.
kΩ, R13 = 2.4 kΩ, R14 = 2.2 kΩ, R1
5 = 5.1kΩ resistance value, V _GG = -5V, V _DD
= + 5V, the drain current of the field effect transistor 31 is 10.
Assuming that 3 mA flows, the voltage drop across the resistor R11 causes 3.1 in the drain of the field effect transistor 31.
A drain voltage of V is applied.

As described above, when the gate bias power source 32 and the drain power source 33 are normal, the voltage V _{B at} the connection point of the resistors R14 and R15 is about 0.3 V, and the base current does not flow, so that the protection transistor 34 is turned on. It is turned off. Then, the microwave signal applied to the gate from the input terminal 40 via the matching circuit 36 is amplified by the field effect transistor 31, and the matching signal from the drain to the matching circuit 37.
Is output to the output terminal 41 via the, and added to the microwave circuit in the subsequent stage (not shown). The inductances 38 and 39 are for blocking microwave signals, and a capacitor (not shown) for blocking DC current is generally provided on the matching circuits 36 and 38 side.

When a voltage is applied from the drain power supply 33 to the drain of the field effect transistor 31 and the gate bias voltage is not applied to the gate due to a delay in the rising of the voltage of the gate bias power supply 32 or an obstacle, that is, V
_{When GG} = 0V, the drain current of the field effect transistor 31 increases, and deterioration is promoted or burned out.

Therefore, the protection transistor 34 is provided, and when the gate bias voltage is not applied to the gate of the field effect transistor 31 (V _GG = 0).
V), the protection transistor 34 is turned on. That is, as described above, if the values of the resistors R13 to R15 are selected, the voltage V _{B at} the connection point of the resistors R14 and R15 is about 0 when the gate bias power source 32 and the drain power source 33 are normal. Since it becomes 0.3 V, the base current does not flow, and the protection transistor 34 is turned off. However, when the gate bias voltage is not applied (V _GG = 0V) due to a delay in the rise of the voltage of the gate bias power source 32 or an obstacle, the voltage V _{B at} the connection point of the resistors R14 and R15 rises and the base current flows. , The protection transistor 34 is turned on.

As described above, when the protection transistor 34 is turned on, the drain of the field effect transistor 31 is grounded, and an increase in drain current can be prevented. Thereby, the deterioration or burning of the field effect transistor 31 can be prevented.

[0010]

As described above, the increase of the drain current of the field effect transistor 31 when the gate bias voltage is not applied is prevented by the protection transistor 34.
Can be suppressed by turning on. However, since the current flowing through the resistor R11 in a normal state is 10.3 mA, the power consumption is about 20 mW, which means that a (1/10) W type chip resistor can be used, but when the gate bias voltage is 0 V. Is the collector-emitter voltage of the protection transistor 34 in the ON state, for example, 0.2
Assuming V, the power consumption of the resistor R11 is about 130 mW. Therefore, a plurality of (1/10) W type chip resistors are connected in parallel so as to have a desired resistance value, or (1 /
4) It is necessary to use a W type chip resistor. That is, there is a problem in that the cost of the resistor R11 and the installation space increase because of the protection of the field effect transistor 31 when the gate bias voltage is not applied, and the protection transistor 3 is used.
4 and the bias adjusting transistor 35 have different conductivity types, and it is necessary to prepare two types of transistors. The present invention aims to economically protect field effect transistors.

[0011]

The amplifier circuit of the present invention will be described with reference to FIG. 1. A gate bias power supply 2 for applying a gate bias voltage to the gate of the field effect transistor 1 and the field effect transistor. In an amplifier circuit that uses two power supplies, a drain power supply 3 and a drain power supply 3 for applying a drain voltage to the drain of 1, the gate bias power supply 2 turns on due to the voltage difference between the gate bias power supply 2 and the drain power supply 3, A protection transistor 4 which is turned off when a gate bias voltage is not applied to the gate of the effect transistor 1 is connected between the drain power supply 3 and the drain of the field effect transistor 1. The illustration of the matching circuit on the input / output terminal side, the inductance for passing only direct current, and the like is omitted.

A second gate is provided on the field effect transistor 1.
A gate bias power supply 2 for applying a gate bias voltage via the resistor 7 and a drain power supply 3 for applying a drain voltage to the drain of the field effect transistor 1 via the first resistor 6. In the amplifier circuit used, a plurality of resistors 8, 9, 10 are connected in series between the gate bias power source 2 and the drain power source 3, and the gate bias power source 2 and the drain power source obtained by the connection point of the resistors 8, 9 are connected. The protection transistor 4 which is turned on due to the voltage difference between the gate voltage of the field effect transistor 1 and the gate of the field effect transistor 1 is turned off when the gate bias voltage is not applied from the gate bias power supply 2 to the drain power supply via the first resistor 6. 3 and the drain of the field effect transistor 1, and between the gate and the drain of the field effect transistor 1. A structure connecting a bias adjustment transistor 5 that automatically adjusted according to the gate bias voltage of the transistor 1 to the drain current.

[0013]

When the gate bias power supply 2 and the drain power supply 3 are normal and the gate bias voltage is applied to the gate of the field effect transistor 1 and the drain voltage is applied to the drain, the base of the protection transistor 4 is used. The voltage at the connection point of resistors 8 and 9 is set so that the current flows,
The protection transistor 4 is turned on. Therefore, a voltage is applied from the drain power source 3 to the drain of the field effect transistor 1 via the transistor 4 in the ON state and the first resistor 6. When the gate bias voltage is not applied, the base potential of the protection transistor 4 becomes almost equal to the emitter potential, and the protection transistor 4 is turned off. Therefore, the drain current of the field effect transistor 1 can be cut off.

Further, the bias adjusting transistor 5 has a first
Of the gate bias voltage of the field effect transistor 1 corresponding to the drain current by selecting the resistor 6 and the second resistor 7 of FIG. 1 and the resistors 8, 9, and 10 connected between the gate bias power source 2 and the drain power source 3. Can be automatically adjusted. Further, by selecting the resistors 8, 9 and 10, when the gate bias voltage is applied to the gate of the field effect transistor 1, the base current of the protection transistor 4 is made to flow, and when the gate bias voltage is not applied, It is possible to prevent the base current from flowing to the protection transistor 4, whereby the protection transistor 4 is turned off when the gate bias voltage is not applied.
The field effect transistor 1 can be protected.

[0015]

EXAMPLE FIG. 2 is an explanatory view of an example of the present invention.
Is a field effect transistor, 12 is a gate bias power supply,
13 is a drain power supply, 14 is a pnp type protection transistor, 15 is a pnp type bias adjustment transistor,
16 and 17 are matching circuits, 18 and 19 are inductances,
20 is an input terminal, 21 is an output terminal, and R1 to R5 are resistors.

The field-effect transistor 11 is a GaAs field-effect transistor similar to the above-mentioned conventional example, and shows an n-channel depletion type case. Then, a gate bias voltage is applied from the gate bias power supply 12 to the gate of the field effect transistor 11 via the second resistance R2 and the inductance 18, and the drain power supply 13 connects the protection transistor 14 and the first resistance R1. The drain of the field-effect transistor 11 is connected to the drain via the drain-voltage.

Further, resistors R3, R4 and R5 are connected between the gate bias power source 12 and the drain power source 13 to connect the resistor R
A pnp-type protection transistor 14 is provided at a connection point between R3 and R4.
Of the pnp type bias adjusting transistor 15 is connected to the connection point of the resistors R4 and R5.
The collector of the bias adjusting transistor 15 is connected to the gate side of the field effect transistor 11, and the emitter is connected to the drain side of the field effect transistor 11. The resistors R1 to R5 are, for example, R1 = 180Ω, R
2 = 10 kΩ, R3 = 680Ω, R4 = 2 kΩ, R5 =
It can be selected to be 7.5 kΩ. Further, the voltage V _GG of the gate bias power supply 12 is -5 V, the voltage V _DD of the drain power supply 13 is +5 V, the drain current of the field effect transistor 11 at that time is 10 mA, and the collector-emitter voltage of the protection transistor 14 is 0.2 V. Then, a voltage of 3V is applied to the drain of the field effect transistor 11.

Gate bias power supply 12 and drain power supply 1
3 is normal, the microwave signal applied to the gate from the input terminal 20 via the matching circuit 16 is amplified by the field effect transistor 11, and is omitted from the output terminal 21 via the matching circuit 17. It is added to the microwave circuit in the latter stage. Such a field effect transistor 1
During the amplifying operation of No. 1, the base potential of the bias adjusting transistor 15, that is, the potential at the connection point of the resistors R4 and R5 is constant at about 2.4 V, but the emitter potential is the first.
Because of the voltage drop due to the resistance R1 of the gate bias voltage, it changes in inverse proportion to the drain current of the field effect transistor 11, and the gate bias voltage is automatically adjusted so as to make the drain current constant.

Also, the base potential of the protection transistor 14,
That is, the potential at the connection point of the resistors R3 and R4 is 4. If the gate bias power supply 12 and the drain power supply 13 are normal.
Since it is constant at 4V and the emitter potential of the protection transistor 14 is + 5V, the base current flows and the ON state is maintained. When the gate bias voltage is not applied (V _GG = 0V) due to a delay in rising of the voltage of the gate bias power supply 12 or an abnormality, the potential at the connection point of the resistors R3 and R4 becomes about 4.67V, and the emitter-base The voltage between them becomes about 0.33V, and the protection transistor 14
Is turned off.

When the protection transistor 14 is turned off,
Since the drain current of the field effect transistor 11 stops flowing, the current flowing through the resistor R1 also becomes zero. That is, the power consumption of the resistor R1 under normal conditions is about 20 mW,
Since the power consumption at the time of an abnormality in which the gate bias voltage is not applied is zero, one (1/10) W type chip resistor is sufficient.

In the above-mentioned embodiment, the field effect transistor 11 as an amplifying element is an n-channel,
It is also applicable to the case of p-channel, and in that case, the conductivity type of the protection transistor 14 and the bias adjustment transistor 15 is changed to the npn type, and the polarities of the gate bias voltage and the drain voltage are inverted. You just have to change the configuration.

[0022]

As described above, according to the present invention, in the amplifier circuit in which the field effect transistor 1 is used as an amplifying element and two power sources of the gate bias power source 2 and the drain power source 3 are used, Even if the drain voltage is applied due to the delay of the rise of the voltage or the abnormality of the gate bias power supply 2, the protection transistor 4 is turned off to shut off the drain current of the field effect transistor 1 when the gate bias voltage is not applied. Therefore, the drain power source 3 and the field effect transistor 1 are
The first resistor 6 connected between the drain and the drain has an advantage that it can be miniaturized because it is not necessary to consider the power consumption only in the normal state and in the abnormal state. Further, since the bias adjusting transistor 5 and the protection transistor 4 can be transistors of the same conductivity type, there is an advantage that the cost can be reduced by using the transistors of the same type.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of an example of the present invention.

FIG. 3 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 Field Effect Transistor 2 Gate Bias Power Supply 3 Drain Power Supply 4 Protective Transistor 5 Bias Adjusting Transistor 6 First Resistor 7 Second Resistor 8, 9, 10 Resistor

Claims (2)

[Claims] 1. A gate bias power source (2) for applying a gate bias voltage to the gate of a field effect transistor (1), and a drain power source (2) for applying a drain voltage to the drain of the field effect transistor (1). 2 with 3)
In an amplifier circuit using a power supply, the gate bias power supply (2) and the drain power supply (3) are turned on by a voltage difference between the gate bias power supply (2) and the gate of the field effect transistor (1). An amplifier circuit comprising a protection transistor (4) which is turned off when a gate bias voltage is not applied to the drain power supply (3) and the drain of the field effect transistor (1). 2. A gate bias power supply (2) for applying a gate bias voltage to the gate of the field effect transistor (1) through a second resistor (7), and a drain of the field effect transistor (1). In an amplifier circuit using two power supplies, a drain power supply (3) for applying a drain voltage via a first resistor (6), the gate bias power supply (2) and the drain power supply (3) A plurality of resistors (8, 9, 10) are connected in series between them, and an ON state is caused by a voltage difference between the gate bias power source (2) and the drain power source (3) obtained by a connection point of the plurality of resistors. Therefore, the protection transistor (4) which is turned off when the gate bias voltage is not applied to the gate of the field effect transistor (1) from the gate bias power supply (2) is used as the protection transistor (4). (6)
Is connected between the drain power source (3) and the drain of the field effect transistor (1) via the drain power source (3) and between the gate and the drain of the field effect transistor (1). An amplifier circuit, to which a bias adjusting transistor (5) for automatically adjusting the gate bias voltage of (1) according to the drain current is connected.