JPH11355054A - High frequency amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency amplifier whose bias voltage is held to be optimum, whose input/output characteristic is not deteriorated and whose distortion rate of output is not deteriorated even if the operation level of an input signal fluctuates. SOLUTION: The high frequency amplifier is provided with a current detection circuit 11, a control circuit 12 and a bias voltage adjusting circuit 13. The current flowing to an NPN transistor 1 from a main power source through a resistor 10 and the like is obtained. The operation level of an input signal at that time is estimated from the current and optimum bias voltage against the input signal is obtained. Then, optimum bias voltage is applied to the base of the NPN transistor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency amplifier for automatically correcting an output distortion factor, and more particularly to a modulated wave related to frequency modulation or phase modulation (modulation in which transmission information is not represented by a change in carrier wave amplitude). The present invention relates to a device suitable for a high-frequency amplifier built in a receiver for receiving a signal.

[0002]

2. Description of the Related Art FIG. 3A shows a configuration of a conventional general high-frequency amplifier. That is, NPN as an amplifying element
An input is applied to the base of the transistor 1 via an input matching circuit 2, and the base has a choke coil 4 for preventing high frequency, a bias voltage stabilizing diode 5 for temperature compensation, and a current limiting resistor. 6 and 7
And a bias circuit is connected to minimize fluctuations in the bias voltage. The collector of the NPN transistor 1 is connected to a power supply (main power supply) for supplying DC power to the high-frequency amplifier via a choke coil 9 for high-frequency blocking, and the output matching circuit 3 is connected to the power supply. The NPN transistor 1 is connected to the output terminal of the high-frequency amplifier, and the emitter of the NPN transistor 1 is grounded.

[0003]

In the above-described high-frequency amplifier, the bias power supply voltage applied via the current limiting resistor 6 of the bias circuit is made constant, and the bias circuit is provided to Voltage fluctuation is suppressed as much as possible.

However, even when the high-frequency amplifier is operated with the bias voltage supplied from the bias circuit kept constant as described above, the operating point shifts depending on the level of operation (amplitude of the input signal). That is, since the high-frequency amplifier is a class AB amplifier in consideration of power efficiency, a bias voltage applied from a bias power supply via the bias circuit is set to an optimum bias voltage for an input signal of a certain operation level. However, it is not optimal for input signals of other operation levels. If the bias voltage deviates from the optimal one, the distortion rate of the output of the high-frequency amplifier deteriorates.

FIG. 3B shows a bias voltage applied to the base from a bias power supply via the bias circuit.
This is an input / output characteristic when the operation level of the input signal is changed after being fixed so as to be optimal for the input signals of the operation levels L2 to L3 in FIG. As can be seen from the figure, the output signal is proportional to the input signal in the range of the operation levels L2 to L3, but in other ranges, the bias voltage is not optimal, so that the input signal deviates from the proportionality and the input / output characteristics are deviated. Are degraded (they deviate from the ideal characteristics as shown by the one-dot chain line in the figure). And when the input / output characteristics deteriorate,
During the amplitude operation, the output distortion rate is degraded.

[0006] The present invention has been made in view of the above circumstances, and even if the operation level of the input signal fluctuates,
It is an object of the present invention to provide a high-frequency amplifier in which the bias voltage is maintained at an optimum value and the input / output characteristics are not degraded, and the output distortion is not degraded.

[0007]

A high-frequency amplifier for receiving a high-frequency signal, amplifying the signal, and outputting the amplified signal is constructed as follows. That is, a current detection circuit that detects a current value of a current flowing from the main power supply of the high-frequency amplifier to the high-frequency amplifier, and a bias voltage adjustment circuit that adjusts a bias voltage applied to the high-frequency amplifier under the control of a control circuit described below. Controlling the bias voltage adjustment circuit based on the current value detected by the current detection circuit, and adjusting the bias voltage to the bias voltage adjustment circuit so that the distortion rate of the output of the high-frequency amplifier is reduced. And a control circuit for adjustment.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described based on embodiments of the invention shown in the drawings. FIG.
FIG. 3A shows the configuration of the embodiment, and each circuit section having the same configuration and the same function as each circuit section in FIG. The reference numerals are attached to the units, and the description of these circuit units is omitted.

A resistor 10 is inserted and connected between the main power supply and the choke coil 9. A current detection circuit 11 takes in the potential at both ends of the resistor 10 and obtains the difference between the two potentials, that is, the resistor 10 , A current value of a current flowing from the main power supply through the resistor 10 and the choke coil 9 to the NPN transistor 1 is obtained from the voltage drop, and the current value is sent to the control circuit 12 described later. It is a circuit part. A bias voltage adjusting circuit 13 to which a bias power supply voltage is applied adjusts (increases or decreases) the bias voltage applied to the base of the NPN transistor 1 via the choke coil 4 under the control of the control circuit 12 described below. It is. The control circuit 12 takes in the current value from the current detection circuit 11, sends a control output corresponding to the current value to the bias voltage adjustment circuit 13, and outputs the bias voltage to the bias voltage adjustment circuit 13. This is a circuit section for adjusting the output sent through the matching circuit 3 or the like to reduce the distortion factor.

Next, the operation of this embodiment having such a configuration will be described. For example, an input signal of a certain operation level is input, and an optimum bias voltage for the operation level is given from the bias voltage adjustment circuit 13 to the base of the NPN transistor 1 via the choke coil 4. State. From this state,
When the operation level changes to a state where an input signal different from the above operation level is input, the following circuit operation is performed. That is, the change in the operation level causes a change in the current flowing from the main power supply into the NPN transistor 1 via the resistor 10 and the choke coil 9, and the current detection circuit 11 detects the current value after the change, The new current value is sent to the control circuit 12. And the control circuit 12
Sends a control output corresponding to the new current value sent from the current detection circuit 11 to the bias voltage adjustment circuit 13,
By controlling the bias voltage adjusting circuit 13, the bias voltage sent from the bias voltage adjusting circuit 13 and applied to the base of the NPN transistor 1 is switched to the optimum one for the input signal of the new operation level. With the above-described circuit operation, even if an input signal of any operation level is input, an optimum bias voltage for the input signal is applied to the base of the NPN transistor 1, and as a result, The deterioration of the distortion factor of the output from the high-frequency amplifier is automatically corrected to a small value.

[0011]

FIG. 2 shows the configuration of the above embodiment (see FIG. 1).
At a more specific level (note that
In FIG. 2, each circuit unit having the same function and the same configuration as each circuit unit shown in FIG. 1 is given the same reference numeral as that given in FIG. However, in the embodiment of FIG.
The current detection circuit 11 and the control circuit 12 in FIG.

In the control unit 14, an analog
The digital converter 28 is a circuit unit that takes in the main power supply voltage (that is, the voltage before the voltage drop at the resistor 10), converts this into digital data, and sends it to the CPU 26.
The analog-to-digital converter 27 is a circuit unit which takes in the voltage after the voltage drop at the resistor 10, converts it into digital data and sends it to the CPU 26. Also ROM
Reference numeral 25 denotes a table that associates each current value of the current flowing into the NPN transistor 1 from the main power supply with the optimum bias voltage at the time of operation at each current value, and the CPU 26.
Is a memory that fixedly stores a program for instructing various operations.

The CPU 26 fetches data sent from the analog / digital converters 27 and 28 in accordance with a program stored in the ROM 25,
From these, the voltage drop at the resistor 10 is determined, then the current value flowing through the resistor 10 is determined from the voltage drop, and the current value and the table stored in the ROM 25 are referred to. An output required to obtain an optimum bias voltage for the signal and further transmitted to the bias voltage adjusting circuit 13 when the optimum bias voltage is actually applied to the base of the NPN transistor 1, that is, a reference voltage. Find output (digital data)
This reference voltage output is converted to digital / analog converter 2
4 is a circuit section to be sent out. The digital / analog converter 24 is a circuit unit which converts the received reference voltage output into an analog reference voltage output and sends it to the bias voltage adjustment circuit 13.

The bias voltage adjusting circuit 13 includes voltage adjusting transistors 20 and 21, a resistor 29, a DC amplifier 22 with a voltage comparison function, and a Zener diode 23, and outputs the reference voltage output from the control unit 14 to the voltage adjusting circuit. This is a circuit section that inputs the base voltage of the transistor 21 and outputs a bias voltage corresponding to the reference voltage output as an optimum bias voltage for the input signal at that time.

This embodiment has the following structure.
The operation described in the description of the embodiment (see FIG. 1) is performed.

The high-frequency amplifier according to the present invention receives a modulated wave such as an amplitude modulation which expresses transmission information by a change in the amplitude of a carrier wave in consideration of the response of a control circuit (including a CPU and the like). Although it is difficult to use it as a high-frequency amplifier built in a receiver, it is used as a high-frequency amplifier built in a receiver that receives a modulated wave (a modulated wave whose amplitude does not change every moment) related to frequency modulation or phase modulation. Is extremely useful.

[0017]

As described in detail above, according to the present invention,
Even if the operation level of the input signal fluctuates, it is possible to provide a high-frequency amplifier in which the bias voltage is maintained at an optimum level and the input / output characteristics are not degraded, and the output distortion is not degraded.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an example that more specifically illustrates the above embodiment.

FIG. 3 is a diagram showing a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 NPN transistor 2 input matching circuit 3 output matching circuit 4 choke coil 5 bias voltage stabilizing diode 6 current limiting resistor 7 current limiting resistor 9 choke coil 10 resistor 11 current detection circuit 12 control circuit 13 bias voltage adjustment circuit 14 control section Reference Signs List 20 voltage adjustment transistor 21 voltage adjustment transistor 22 DC amplifier with voltage comparison function 23 zener diode 24 digital / analog converter 25 ROM 26 CPU 27 analog / digital converter 28 analog / digital converter

Claims (1)

[Claims] 1. A high-frequency amplifier that inputs a high-frequency signal, amplifies and outputs the high-frequency signal, and a current detection circuit that detects a current value of a current flowing from a main power supply of the high-frequency amplifier to the high-frequency amplifier. A bias voltage adjustment circuit that adjusts a bias voltage applied to the high-frequency amplifier under the control of the control circuit; and controls the bias voltage adjustment circuit based on the current value detected by the current detection circuit to control the bias voltage. A high-frequency amplifier, comprising: a control circuit that adjusts the bias voltage so that a distortion rate of an output of the high-frequency amplifier is reduced with respect to the adjustment circuit.