JPS6351707A - High frequency amplifier - Google Patents

Abstract

PURPOSE:To perform temperature compensation without using a temperature detector, by detecting the quantity of a main bias signal to a semiconductor amplifying element, and compensating the temperature characteristic of the gain of the semiconductor amplifying element by controlling a variable attenuator by the detecting signal. CONSTITUTION:A high frequency signal inputted through a high frequency signal input terminal 1, is attenuated by a PIN diode variable attenuator 4, and is amplified by a high frequency amplifying part 3, and is outputted from a high frequency signal output terminal 2. At this time, a bias current to the PIN diode variable attenuator 4 is controlled corresponding to the value of a drain current detected at a resistor 6. In other words, the bias current of the PIN diode variable attenuator 4 is controlled so that the more the total quantity of the drain current increased, the more the attenuated quantity of the PIN diode variable attenuator 4 increased, and the less the total quantity of the drain current decreased, the less the attenuated quantity of the PIN diode variable attenuator 4 decreased. In this way, it is possible to perform the temperature compensation of the high frequence gain in the whole of the high frequency amplifier.

Description

[Detailed Description of the Invention] [Field of Application in M Industry] This invention is applicable to field effect transistors (FETs), for example.
The present invention relates to a high-frequency amplifier using an amplifying element.

[Prior Art] FIG. 3 is a block diagram of a conventional high-frequency amplifier. In the figure, 1 is a high-frequency signal input terminal, 2 is a high-frequency signal output terminal, 3 is a high-frequency amplification section using a field-effect transistor as an amplification element, 4 is a PIN diode variable attenuator, 5 is a train power supply for the high frequency amplifier section 3, 7 is a bias current control circuit for the PIN diode variable attenuator 4, and 8 is a temperature detector for detecting the temperature near the high frequency amplifier section 3.

Next, the operation will be explained. A high frequency signal input through the high frequency signal input terminal 1 is attenuated by the PIN diode variable attenuator 4, amplified by the high frequency amplification section 3, and outputted from the high frequency signal output terminal 2. Here, semiconductor amplification elements such as field-effect transistors are widely used as the high-frequency amplification section 3, but especially in the case of field-effect transistors, the high-frequency gain generally increases when the ambient temperature is low; There is a characteristic that the high frequency gain decreases as the temperature increases. In order to reduce this gain fluctuation, a temperature detector 8 such as a thermistor or thermocouple is used to detect changes in the ambient temperature near the high frequency amplification section 3. When the ambient temperature increases, the amount of attenuation of the PIN diode variable attenuator 4 increases. The bias current control circuit 7 controls the bias current of the PIN diode variable attenuator 4 so that the bias current increases, thereby performing temperature compensation for the gain of the entire high frequency amplifier.

[Problems to be Solved by the Invention] Conventional high-frequency amplifiers are configured as described above, so 1. In a wide ambient temperature range such as -306C to +50°C, an inexpensive temperature detector 8 such as a thermistor is used. Then, due to deterioration in the linearity of the detector itself and variations in its characteristics, a sufficient temperature compensation effect cannot be obtained. Therefore, it is necessary to add a linearization circuit or to select a temperature detector with uniform characteristics. There was a problem.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a high frequency amplifier that can perform temperature compensation without using a temperature detector.

Means for Solving Problem c] The high frequency amplifier according to the present invention detects the amount of the main bias signal to the semiconductor amplification element, controls the variable attenuator with the detection signal, and adjusts the temperature of the gain of the semiconductor amplification element. It is configured to compensate for the characteristics.

[Function] The high-frequency amplifier of the present invention increases the attenuation of the variable attenuator when the amount of the main bias signal to the semiconductor amplification element increases, and increases the amount of attenuation of the variable attenuator when the amount of the main bias signal to the semiconductor amplification element decreases. It operates to reduce the amount of attenuation.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. 1st
FIG. 1 is a block diagram showing a high frequency amplifier as an embodiment of the present invention. In FIG. 1, high frequency signal input terminals 1. A high frequency amplification section 3 consisting of a high frequency signal output terminal 2 and a field effect transistor as a semiconductor amplification element. PIN
The diode variable attenuator 4 and the drain power supply 5 for supplying the field effect transistor train current (main bias signal) are the same as in the conventional example shown in FIG. 6 is a resistor connected in series to the drain power supply line.

This resistor 6 functions as a detection section that detects the drain current a. 7 is a bias current control circuit for the PIN diode variable attenuator 4 as in the above conventional example; Control bias current.

Next, the operation of the embodiment will be explained. Figure 2 is 140H
2? High frequency amplifier operating at iF (this high frequency amplifier has 5 stages of grounded source field effect transistors)
This is an example showing the temperature characteristics of the total drain current and small signal gain of . The following can be seen from this Figure 2. That is, the total drain current tends to decrease as the ambient temperature increases, and increases as the ambient temperature decreases, and a strong correlation with the temperature characteristics of the small signal gain is recognized. Therefore, the total drain current is detected, and if the total drain current increases, the attenuation amount of the PIN diode variable attenuator 4 is increased, and if the total drain current decreases, the attenuation amount of the PIN diode variable attenuator 4 is decreased. By controlling the bias current of the PIN diode variable attenuator 4, temperature compensation of the high frequency gain of the entire high frequency amplifier can be performed.

Note that although the above embodiment uses a field effect transistor as the semiconductor amplification element constituting the high frequency amplification section, other semiconductor elements whose main bias current value exhibits temperature characteristics similar to those of the field effect transistor may be used.

[Effects of the Invention] As described above, according to the present invention, the structure is such that the temperature characteristics of the gain of the high frequency amplifier can be compensated for without using a temperature detector as in the conventional case.

There is no need for a linearization circuit, component selection, etc., which are required when using a temperature detector, and this has the effect that the device can be provided at a low cost.

[Brief Description of the Drawings] Fig. 1 is a block diagram of a high-frequency amplifier according to an embodiment of the present invention, and Fig. 2 shows an example of the temperature characteristics of the total drain current and high-frequency gain of a high-frequency amplifier using field-effect transistors. FIG. 3 is a configuration diagram of a conventional high frequency amplifier. In the figure, 1 - high frequency signal input terminal, 2 - high frequency signal output terminal, 3 - high frequency amplification section using a field effect transistor amplification element, 4 - PIN diode variable attenuator, 5 - drain power supply, 6 - drain current Detection resistor,
7-PIN diode variable attenuator bias current control circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A variable attenuator capable of attenuating a high frequency input signal and changing the amount of attenuation, and a high frequency amplification section made of a semiconductor amplification element to amplify the output from the variable attenuator, and a semiconductor of the high frequency amplification section. A detection section that includes a power supply that supplies a main bias signal to the amplification element and detects the amount of the main bias signal, and a control section that controls the amount of attenuation in the variable attenuator based on the detection signal from the detection section. A high frequency amplifier characterized by: