JPH0590846A - High frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To reduce power leakage when amplification operation stops by turning on the first switch and turning off the second switch when amplification acts and by turning off the first switch and turning on the second switch when amplification stops. CONSTITUTION:A high frequency signal from input terminal 11 passes through capacitor 12 and is input in the base of transistor (Tr) 17. On the other hand, from power supply 20 a voltage is applied to the collector of transistor Tr 17. Further, the first switch 15 and the second switch 16 are turned on and off by means of mutually reverse logic. When switch 15 is turned on, switch 16 is turned off, whereby a predetermined base bias voltage is applied to transistor Tr 17 by resistors 13 and 14, and whereby the Tr 17 acts to amplify a high frequency signal and to output the amplified signal to output terminal 19 via capacitor 18. On the other hand, when switch 15 is turned off, the aforementioned process becomes reverse, whereby the base of Tr 17 is not supplied with a bias voltage. Moreover, switch 16 causes Tr 17 to be set at a potential common to switch 16, whereby Tr 17 is cut off, whereby Tr 17 stops amplification operation, thereby reducing power leakage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a high frequency amplifier circuit which performs a switching operation for controlling "on" and "off" a high frequency output signal.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional high frequency amplifier circuit.

Conventionally, a high frequency amplifier circuit has a structure as shown in FIG. In FIG. 3, 11 is an input terminal, 1
Reference numerals 2 and 18 are capacitors for cutting direct current, 13 and 14 are resistors for giving a bias, 41 is a switch, 17 is a transistor, 19 is an output terminal, and 20 is a power supply.

The high frequency signal input to the input terminal 11 when the switch 41 is in the "on" state is amplified by the transistor 17 and output to the output terminal 19. On the other hand, switch 4
Since the bias is not applied to the transistor 17 when 1 is “off”, the high frequency signal input to the input terminal 11 is output to the output terminal 19 through the capacitor 12, the collector capacitance of the transistor 17 and the capacitor 18.

Therefore, the leakage power that appears at the output terminal 19 when the switch 41 is in the "off" state is
2 and 18 are generally the collector capacitance C of the transistor 17.
_Since it is much larger than _0b, it is dominated by the collector capacitance C _0b of the transistor 17.

[0006]

However, in such a conventional high frequency amplifier circuit, when the switch is "off", all the voltages applied to the transistors are cut off, so that the collector terminal and the emitter are disconnected. The potential difference between the terminals becomes "0", and the collector capacitance C _0b between the collector and the base increases as compared to when the switch is in the "ON" state, resulting in a large leakage power of the high frequency signal appearing at the output terminal. was there.

The present invention solves the above problems.
An object of the present invention is to provide a high frequency amplifier circuit capable of gradually reducing leakage power when the amplification action is stopped.

[0008]

According to the present invention, there is provided a transistor for amplifying a high frequency signal, a power supply for applying a voltage to a collector of the transistor through a first resistor, a collector and a base of the transistor, and In a high-frequency amplifier circuit having a second resistor and a third resistor which are respectively inserted between the base and a common potential to provide a bias, the high frequency amplifier circuit is inserted between the collector of the transistor and the second resistor. It is characterized by comprising a first switch and a second switch which is connected in parallel to the third resistor and which operates with a control logic reverse to that of the second switch.

Further, according to the present invention, the first switch and the second switch may be composed of transistors.

[0010]

[Function] During the amplifying operation, the first switch inserted between the collector of the transistor and the second resistor is turned “on”.
Then, the second switch connected in parallel with the third resistor is turned “off”. When the amplification operation is stopped, the first switch is turned “off”, the second switch is turned “on”, the voltage is kept applied to the collector, and the emitter and the common potential are short-circuited.

As described above, the leakage power when the amplification action is stopped can be gradually reduced.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a high frequency amplifier circuit according to an embodiment of the present invention.

In FIG. 1, the high frequency amplifier circuit includes an input terminal 11, an NPN type transistor 17 whose emitter is connected to a common potential as a transistor for amplifying a high frequency signal, and an input terminal 11 and a base of the transistor 17. A capacitor 12 inserted into the transistor 17, a power supply 20 for applying a “+” voltage to the collector of the transistor 17 as a first resistance via a resistor 21, a collector and a base of the transistor 17, and a base and a common potential. A resistor 13 as a second resistor and a resistor 14 as a third resistor which are respectively connected between the two, a capacitor 18 connected to the collector of the transistor 17, and an output terminal 19 connected to the capacitor 18. ..

The feature of the present invention is that the switch 15 is a first switch inserted between the collector of the transistor 17 and the resistor 13, and the switch 15 is connected in parallel with the resistor 14 and is opposite to the switch 15. The switch 16 is provided as the second switch that operates by the control logic.

The operation of the high frequency amplifier circuit having such a configuration will be described.

In FIG. 1, the high frequency signal input to the input terminal 11 passes through the capacitor 12 and the transistor 17.
Supplied to the base of.

On the other hand, a voltage is applied from the power source 20 to the collector terminal of the transistor 17. The switch 15 and the switch 16 perform "on" and "off" operations with mutually opposite logics. When the switch 15 is “on”, the switch 16 is “off”, and the resistor 13 and the resistor 1
A required base bias voltage is applied to the transistor 17 by the transistor 4, and the transistor 17 is activated to amplify a high frequency signal, and the output terminal 1 is output via the capacitor 18.
Output to 9.

Further, since the switch 16 is controlled to be turned on when the switch 15 is "off", a bias voltage is not supplied to the base and the switch 16 becomes the same potential as the common potential, so that the transistor 17 is turned on. It becomes "cut off" and the amplification operation is stopped. At this time, the high frequency signal level output to the output terminal 19 is determined by the emitter capacitance C _ib between the base and the emitter (common potential) and the collector capacitance C _0b between the collector and the base.
FIG. 4 shows the case where the collector capacitance C _0b and the emitter capacitance C _ib of the transistor 17 are changed respectively between the collector-base voltage V _CB and the base-emitter voltage V _EB . From FIG. 4, the collector capacitance C _0b shows a smaller value when a voltage is applied between the collector and the base, and the emitter capacitance C _ib shows a larger value so that there is no voltage difference between the base and the emitter. From these relationships, transistor 1
In order to reduce the leakage power when "OFF" of 7, the collector terminal voltage of the transistor 17 is always applied as described above, and the base terminal voltage is the emitter (common voltage).
It can be realized by setting the same potential as.

FIG. 2 is a circuit diagram of a high frequency amplifier circuit according to another embodiment of the present invention. 2 shows the switches 15 and 16 of FIG.
A circuit diagram when realized by P and NPN type transistors is shown. By inputting a signal of a logic voltage having the same potential as the power supply 20 to the control terminal 27, the transistor 17 performs “on” and “off” operations. When the control terminal 27 is "L", the transistor 25 is "on", the transistor 26 is "off", the bias voltage determined by the resistors 13 and 14 is applied to the transistor 17, and the transistor 17 performs an amplifying operation. A high frequency signal is output to the output terminal 19.

When the control terminal 27 is "H", the transistor 25 is "off" and the transistor 26 is "on".
Since the base potential of the transistor 17 becomes the same potential as the common potential, the transistor 17 is in the “cutoff” state. At this time, the capacitance of the emitter capacitance C _ib has the maximum value and the collector capacitance C _0b between the collector and the base has the minimum value, so that the leakage of the high frequency signal to the output terminal 19 can be reduced.

[0021]

As described above, the present invention has an excellent effect that the leakage power when the amplification operation is stopped can be gradually reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high frequency amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a high frequency amplifier circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional high frequency amplifier circuit.

FIG. 4 is a diagram showing a relationship between a collector-base voltage and a base-emitter voltage of a high-frequency amplifier circuit, and collector capacitance and emitter capacitance.

[Explanation of symbols]

 11 Input Terminals 12, 18 DC Cutting Capacitors 13, 14, 21 Biasing Resistors 15, 16 Switches 17 High Frequency Amplification Transistors 19 Output Terminals 20 Power Supplies 25, 26 Switch Transistors 27 Control Terminals

Claims (2)

[Claims] 1. A transistor for amplifying a high frequency signal,
A power source for applying a voltage to the collector of the transistor via the first resistor, and a second resistor and a second resistor which are respectively inserted between the collector and the base of the transistor and between the base and the common potential to provide a bias. In a high-frequency amplifier circuit including three resistors, a first switch inserted between the collector of the transistor and the second resistor, and a second switch connected in parallel with the third resistor. And a second switch that operates in the opposite control logic. 2. The high frequency amplifier circuit according to claim 1, wherein the first switch and the second switch are transistors.