JP2000244255A - Low distortion amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low distortion amplifier which can obtain a high amplifying gain and can obtain a superior linear characteristic. SOLUTION: That the MOSFET amplifying circuit of an AB class has an opposite characteristic to the GaAsFET amplifier circuit of a C class is aimed and the characteristics of both circuits are synthesized. Thus, a high gain is realized. Namely, the GaAsFET amplifier circuit of the C class and the MOSFET amplifier circuit 12 of the AB class are connected in series. It is desirable that the MOSFET amplifier circuit of the AB class is arranged in an output stage and the GaAsFET amplifier circuit 11 of the C class is arranged in the driver stage preceding thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low distortion linear amplifier constituted by using a transistor amplifier circuit.

[0002]

2. Description of the Related Art A power amplifier circuit using a transistor element has been used in various devices because it can be reduced in size and power consumption can be suppressed. A low distortion amplifier configured using such a transistor amplifier circuit is used, for example, in a receiving unit or a transmitting unit of a base station, a repeater, or a mobile station of a mobile radio communication system. In addition, an amplification characteristic according to the communication system is required.

[0003] As for other communication systems, for example, a CDMA system (a so-called W-CDM system) that spreads and modulates a signal to a relatively wide band using QPSK and transmits the signal.
In the A method), the peak power whose level is higher than the average power by about 10 dB is instantaneous, so that the amplification characteristic of the amplifier requires linearity to suppress distortion.

FIG. 5 shows a configuration of a conventional low distortion amplifier using a field effect transistor (hereinafter referred to as GaAsFET) using GaAs (gallium arsenide).
This low distortion amplifier is obtained by connecting a linearizer 1 and an amplifier circuit 2 composed of GaAs FETs in series.
The linearizer 1 achieves linearity by compensating for the characteristics of the GaAs FET amplifier circuit 2.

That is, the input power (Pin) -output power (Pout) characteristic of the GaAs FET amplifier circuit 2 is shown in FIG.
(A), and the input power (Pin) −
The phase (Φ) is as shown in FIG. 7B, and does not have linearity. Therefore, the input power (P
FIG. 6A shows the relationship between (in) -output power (Pout), and FIG. 6 (a) shows the input power (Pin) -phase (Φ).
As shown in (b), both of which are opposite to the characteristics of the GaAs FET amplifier circuit 2, the linearizer 1 and the Ga
By providing the AsFET amplifier circuit 2 in series,
A linear characteristic obtained by combining the two characteristics is realized.

[0006]

However, the linearizer 1 is an FET which does not apply a diode or a drain voltage.
However, since it is configured using passive elements such as those described above, it does not contribute to the amplification function, and thus has a problem that high gain cannot be obtained. This means that sufficient amplification cannot be achieved for the power consumption. For mobile stations (cellular phones, pagers, mobile tools, etc.) that use a battery as a power source, the operating time of the battery is shortened and the usability is reduced. Is extremely reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a low distortion amplifier capable of obtaining a high amplification gain and obtaining excellent linear characteristics. Further objects of the present invention will be apparent in the following description.

[0008]

SUMMARY OF THE INVENTION The present invention focuses on the fact that an amplifier circuit composed of a MOS field-effect transistor (hereinafter, referred to as a MOSFET) has characteristics opposite to those of a GaAs FET amplifier circuit. A linear characteristic is realized by combining the characteristics, and a high gain is realized by the amplification function of both.

More specifically, a low distortion linear amplifier according to the present invention comprises a class C GaAs FET amplifier circuit and a class AB MOS amplifier.
It is configured by connecting an FET amplifier circuit in series. Also,
More preferably, focusing on the fact that a MOSFET can obtain a larger gain than a GaAs FET, the low distortion amplifier according to the present invention includes an AB class MOSFET amplifier circuit in the output stage and a C class GaAs FET amplifier circuit. It is arranged in the preceding driver stage and realizes high amplification efficiency and high linearity as a whole.

Here, as is well known, the transistor amplifier circuit has a class A, a class AB, a class B,
Divided into C class. The class A amplifier circuit has an operating point set at the center of the load line. When a sine wave voltage is applied to the base, a current similar to that flows to the base, and a similar voltage and current are generated at the collector. Class B amplifier circuit
The operation between the base and the emitter is performed with almost zero bias. Even if a sine wave voltage is applied to the base, the output current flows only for a half cycle. In the class AB amplifier circuit, two transistors are connected by push-pull connection, and the operating point is set between the class A and the class B. The class C amplifier circuit applies a voltage lower than the pinch-off voltage between the base and the emitter.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to an embodiment shown in the drawings. As shown in FIG. 1, the low distortion linear amplifier of the present embodiment is configured by connecting a GaAs FET amplifier circuit 11 and a MOSFET amplifier circuit 12 in series, and disposing the MOSFET amplifier circuit 12 at an output stage (later stage). And the GaAs FET amplification circuit 11 is connected to the driver stage (previous stage).
In order to improve the amplification efficiency as described later.

The GaAs FET amplifier circuit 11 is a class C amplifier circuit, and has an input power (Pin) as shown in FIG.
It has output power (Pout) characteristics and input power (Pin) -phase (Φ) characteristics as shown in FIG.
However, in this example, a low output section showing relatively stable characteristics,
That is, the characteristics of the K portion shown in FIG. The MOSFET amplifier circuit 12 is a class AB amplifier circuit, and has an input power (Pin) as shown in FIG.
It has output power (Pout) characteristics and input power (Pin) -phase (Φ) characteristics as shown in FIG.

Therefore, the signal input from the input terminal is amplified by the GaAs FET amplifier circuit 11, further amplified by the MOSFET amplifier circuit 12, and output from the output terminal. At this time, the C-class GaAs shown in FIG.
The characteristics of the FET amplifier circuit 11 and the AB class MOS shown in FIG.
Due to the combined action with the characteristics of the FET amplification circuit 12, the entire amplification path from the input terminal to the output terminal is shown in FIG.
Linear input power (Pin) -output power (P
4) and a linear input power (Pin) -phase (Φ) characteristic as shown in FIG. 4B. The input signal is amplified with low distortion, high gain, and high linearity and output. Is done.

In the above embodiment, the characteristics of the low output section K of the GaAs FET amplifier circuit 11 are used.
The aAsFET amplifier circuit 11 has a relatively high gain M
Since the amplifier functions as a driver of the OSFET amplifier circuit 12, high amplification efficiency is realized as the whole amplifier. Although such an embodiment is preferable, a class C GaAs FET amplifier circuit and a class AB GaAs FET amplifier exhibiting mutually contradictory characteristics.
By combining with the class MOSFET amplification circuit,
According to the idea of the present invention for obtaining a high gain linear characteristic, these C-class GaAs FET amplifier circuit and AB-class MOS
It is also possible to configure the amplifier by reversing the positional relationship with the FET amplifier circuit.

[0015]

As described above, according to the low distortion amplifier of the present invention, a class C GaAs exhibiting mutually opposite characteristics.
Since the FET amplifier circuit and the AB class MOSFET amplifier circuit are connected in series, a high gain can be obtained by a combination of active element circuits, and amplification with less distortion due to excellent linear characteristics can be realized. it can.
In particular, when the low distortion amplifier according to the present invention is used in a communication processing unit of a mobile station, it is possible to perform high-gain signal amplification with excellent characteristics while suppressing power consumption, thereby extending the battery power life of the mobile station. Usability can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a low distortion amplifier according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a C-class GaAs FET amplifier circuit.

FIG. 3 is a characteristic diagram of a class AB MOSFET amplifier circuit.

FIG. 4 is a characteristic diagram of a low-distortion amplifier illustrating the operation of the present invention.

FIG. 5 is a configuration diagram of a conventional low distortion amplifier.

FIG. 6 is a characteristic diagram of a linearizer.

FIG. 7 is a characteristic diagram of a GaAs FET amplifier circuit.

[Explanation of symbols]

 11: C class GaAs FET amplifier circuit, 12: AB class MOSFET amplifier circuit,

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J090 AA01 AA41 AA63 AA65 CA25 CA32 FA08 FA15 GN03 GN11 HA09 HA10 HA24 MA08 SA14 TA01 TA02 5J091 AA01 AA41 AA63 AA65 CA25 CA32 FA08 FA15 HA09 HA10 HA24 MA08 SA14 TA01 TA02

Claims (2)

[Claims] 1. A low-distortion amplifier comprising a linear amplifier in which a class C amplifier circuit composed of GaAs field-effect transistors and a class AB amplifier circuit composed of MOS field-effect transistors are connected in series. 2. The low-distortion amplifier according to claim 1, wherein a class-AB amplifier composed of MOS field-effect transistors is arranged in an output stage, and a class-C amplifier composed of GaAs field-effect transistors is a driver in the preceding stage. A low distortion amplifier, which is a linear amplifier arranged in stages.