JP2000040928A - Power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power amplifier circuit whose total power efficiency containing a power source is high and moreover whose gain stability is high. SOLUTION: A switching power amplifier circuit 2 is used for the power amplifier stage of a highly precise power amplifier 51, and a rectifier power source device constituted only by a rectifier circuit and a filter circuit is used as a power source device 40. Furthermore, a divider 5 which divides an input signal to the switching power amplifier circuit 2 by the voltage of the power source device 40 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the efficiency of a power amplifier circuit having high input / output linearity and extremely stable amplification factor for industrial use.

[0002]

2. Description of the Related Art A power amplifier that amplifies an analog signal and outputs it as a large power signal has a linear input / output characteristic depending on the application (eg, amplifying various industrial sensor signals and driving an actuator). High (eg 0.1%
), And those with an extremely stable amplification factor (for example, about 0.1%) are required. And something that satisfies these goals has already been obtained. However, these precision amplifiers are generally not operationally efficient in power for various known reasons.

On the other hand, there is a high-efficiency power amplifier using a switching amplifier circuit, but this generally does not have good amplification accuracy (stability). Efficiency is also an important performance in an environment with limited power supply capacity and heat radiation allowance, such as an artificial satellite. Therefore, a high-precision amplifier having excellent power efficiency is required. Hereinafter, in this specification, a high-efficiency high-precision power amplifier having the above performance is simply referred to as a high-precision power amplifier.

FIG. 6 is a circuit diagram of a conventional high-precision power amplifier disclosed in Japanese Patent Application Laid-Open No. 9-260979. In FIG. 1, reference numeral 1 denotes a voltage amplifying circuit for amplifying an input signal 100, which generally has an extremely high gain. Reference numeral 2 denotes a switching power amplifying circuit that receives the output of the voltage amplifying circuit 1 and amplifies the power to output an output signal 200. Reference numeral 3 denotes a feedback circuit that feeds back the output 200 of the switching power amplifying circuit 2 to the input of the voltage amplifying circuit 1 in reverse polarity. In the drawings, the amplifier symbol is used, but it does not always include an active element. Reference numeral 4 denotes a power supply device for supplying a voltage necessary for the operation of each amplifier circuit. Although an AC / DC power supply is shown in the figure, a battery or the like may be used in some cases. In the following description, the amplification factor may be referred to as a gain, but has the same meaning here.

The operation of the conventional high-precision power amplifier 50 shown in FIG. 6 will be described. The amplification factor of the voltage amplifying circuit 1 has a sufficient gain to obtain a necessary total gain (gain between the signal 100 and the signal 200) after performing sufficient negative feedback. For example, when the total gain is 1000, the gain usually is about 100000 times.

[0006] The switching power amplifier circuit 2 is a switching power amplifier realized by a method such as pulse width modulation and has a high efficiency but cannot be said to have a stable gain. In particular, due to the operation principle, the fluctuation of the supplied power supply voltage directly affects the gain of the switching power amplifier circuit 2. FIG. 7 is a characteristic diagram for explaining a change in input / output gain of the switching power amplifier circuit 2 alone with respect to a change in the power supply voltage. The characteristic diagram has a characteristic that is not completely proportional to the power supply voltage but is approximately proportional to the power supply voltage. . The feedback circuit 3
Generally, it is a negative feedback circuit which is constituted only by passive elements so that stable operation can be expected and determines the total gain.
And the gain can be obtained sufficiently stable.

The power supply unit 4 supplies power to the voltage amplification circuit 1, the switching power amplification circuit 2, and, if necessary, the feedback circuit 3. The system of the power supply device 4 is roughly divided into a simple rectifier circuit and a filter circuit (hereinafter referred to as a rectified power supply for convenience of description) and a system having an active voltage control circuit (hereinafter referred to as a stabilizing circuit). However, the voltage stability (the reciprocal of the voltage fluctuation rate) and the operation efficiency are approximately as follows. Power supply method Voltage fluctuation rate Efficiency Rectified power supply 50% 100% Stabilized power supply 1% 70-80% Power supplies using batteries are classified here as rectified power supplies due to their characteristics.

[0008] Here, the efficiency of the high precision power amplifier 50 and
Examine the stability of the amplification rate (the reciprocal of the fluctuation rate). The efficiency of the high-precision power amplifier 50 is so small that the power consumption of the voltage amplifier 1 is negligible.
And the efficiency τ2 of the power supply device 4. It is well known that when the forward gain of the high-precision power amplifier 50 is G and the total gain is 1 / H, the fluctuation rate of the total gain is obtained by multiplying the fluctuation rate of the amplification rate by 1 / GH. .

First, a case where a stabilized power supply is used for the power supply device 4. Assuming that the fluctuation rate of the power supply 4 = 1%, the gain fluctuation rate of the switching power amplifier circuit = 1% The efficiency of the switching power amplifier circuit τ1 = 70 to 80
% Efficiency of the stabilized power supply device 4 τ2 = 70 to 80% Therefore, the total efficiency of the power amplifying unit τ0 = τ1 × τ
2 = 49-64% Gain fluctuation rate = 1 × 1000/100000 = 0.01
% When a rectified power supply is used as the power supply 4. Fluctuation rate of power supply 4 = 50% Gain fluctuation rate of switching power amplifier circuit 2 = 50% Efficiency of switching power amplifier circuit 2 τ1 = 70 to 80
% Efficiency of rectified power supply τ2 = 100% Therefore, total efficiency of power amplifying section τ0 = τ1 × τ
2 = 70-80% Gain fluctuation rate = 50 × 1000/100000 = 0.5
%

That is, when a stabilized power source is used as a power source to obtain stability, the stability is improved, but the efficiency is reduced. When a rectified power source is used as the power source to improve the efficiency, the efficiency is improved, but the stability of the gain is reduced. descend.

[0011]

In a conventional high-precision, high-efficiency power amplifier, even if the power amplifying section is constituted by an efficient switching power amplifying circuit, a stable power supply device is required to obtain gain stability. Power supply must be used. Since a stabilized power supply is generally inefficient, there is a problem that the efficiency of the power amplifier as a whole is reduced.
In addition, it is difficult to use a rectified power supply as a power supply with priority given to efficiency because fluctuations in the power supply voltage become large and the stability of the gain decreases, and it is difficult to further increase the gain of the voltage amplifier circuit. There was a problem that the loop gain became too high and became unstable and difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a power amplifier circuit having high total power efficiency including a power source and high gain stability. .

[0013]

A power amplifying circuit according to the present invention includes an amplifying circuit for amplifying an input signal, a switching power amplifying circuit for receiving and amplifying an output signal of the amplifying circuit, and a switching power amplifying circuit for the switching power amplifying circuit. A feedback circuit that feedbacks an output signal and adds the input signal with a reverse polarity to the input signal, and a power amplifier including a power supply circuit that supplies a power supply voltage to the switching power amplification circuit, wherein the power amplification circuit and the switching power amplification circuit A divider which is interposed therebetween and divides an output signal of the amplifier circuit by the power supply voltage supplied to the switching power amplifier circuit, and sends an output to an input terminal of the switching power amplifier circuit. The divider acts to compensate for fluctuations in the gain of the switching power amplifier due to fluctuations in the power supply voltage.

In the above, the power supply device is a rectified power supply device. The rectified power supply acts to improve power efficiency.

[0015] The divider of the power amplifier circuit according to the present invention comprises:
An impedance element connected between an output terminal of the amplifier circuit and an input terminal of the switching power amplifier circuit, an FET element connected between an input terminal of the switching power amplifier circuit and ground, and a gate terminal of the FET element. It includes a signal circuit for sending a power supply voltage. The FET element receiving the power supply voltage at the gate terminal acts so as to constitute a simple divider with the impedance element.

The signal circuit is a function circuit using a semiconductor element. The function circuit formed by the semiconductor element acts to make the power supply voltage characteristic of the switching power amplifier circuit seemingly linear.

[0017] The divider of the power amplifier circuit according to the present invention comprises:
An electronic regulator whose attenuation rate is controlled by the control signal by the control signal, an A / D converter for converting the power supply voltage into a digital signal, and a control signal corresponding to a change value of the digital signal are selected from a storage table. A ROM for outputting to the electronic volume. By storing data corresponding to the voltage characteristics of the switching power amplifier in the storage table, the electronic volume acts to accurately linearize and compensate the characteristics of the switching power amplifier.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a high-precision power amplifier according to Embodiment 1 of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a voltage amplifying circuit having a sufficient gain for amplifying an input signal 100, 5 denotes a divider (details will be described later) which receives an output of the voltage amplifying circuit 1 and processes the signal.
Is a switching power amplifier circuit that receives the output of the divider 5 and power-amplifies and outputs an output signal 200; 3 is a feedback circuit that feeds back and adds the output 200 of the switching power amplifier circuit to the input of the voltage amplifier circuit 1 in reverse polarity;
Reference numeral 40 denotes a power supply (AC / DC power supply) for supplying a voltage necessary for the operation of each amplifier circuit, which is a rectification power supply including a rectification circuit and a passive element. The divider 5 is a divider circuit that uses the signal (Vid in the drawing) from the voltage amplification circuit 1 as a dividend and the power supply voltage (B in the drawing) supplied to the switching power amplification circuit 2 as a divisor, and outputs (Vi = Vid / B in the drawing). ) Are input to the switching power amplifier circuit 2.

Next, the operation of the high precision power amplifier 51 shown in FIG. 1 will be described. FIG. 2 shows the input / output characteristics of the divider 5 with respect to a change in the input power supply voltage (illustrated B). When the voltage B is low, the gain as the divider is high, and when the voltage B is high, the gain is high. Is configured to be higher. The same conditions as described in the conventional example, that is, the gain G1 of the voltage amplifier 1 is 100,000 times, the total gain G2 of the high-precision power amplifier 51 is 1000 times,
A voltage fluctuation rate of 0 is 50%.

First, the input / output characteristics of the switching power amplifier circuit 2 after the output of the divider 5 are such that the input voltage is Vi, the output voltage is Vo, the gain is G, and the current power supply voltage is a value with respect to a normal value. Assuming that the output of the switching amplifier circuit 2 is proportional to the power supply voltage B, Vo = G × K × Vi / 100 (1) The input / output characteristics of the divider 5 are such that the input is Vid and the output is Vid. As Vd, Vd = (Vid / K) × 100 (2) Accordingly, the total characteristics of the divider 5 and the switching power amplifier circuit 2 are as follows: Vo = G × K × Vi / 100 = G × K × (Vd) / 100 = G × K × (Vid / K) 100/100 = G × Vid (3)

In this way, fluctuations in the power supply voltage are completely compensated. However, it goes without saying that this is a case where it is assumed that the gain fluctuation of the switching power amplifier 2 is proportional to the power supply voltage fluctuation (that is, equation (1) holds). In reality, the gain variation is not proportional to the variation of the power supply voltage as shown in FIG. 7 due to the saturation characteristics of the transistor of the switching power amplifier 2 and the like, so that a slight error remains. This slight error is, for example, 1000/100 under the above-described conditions by the above-described feedback control.
000.

Embodiment 2 FIG. FIG. 3 shows a high-precision power amplifier according to Embodiment 2 of the present invention. FIG. 3 shows a specific example of the divider 5 of FIG.
And bias resistors R7 and R8. The other circuits are the same as those in FIG.

The operation of the circuit shown in FIG. 3 will be described. FE
Assuming that the resistance between S and D of T6 is r, the apparent gain of the divider 5 is represented by r / (R9 + r). When the power supply voltage B of the switching power amplifier circuit 2 is low, the S
−D increases, the input voltage Vi of the switching power amplifier circuit 2 increases, and when the power supply voltage B is high, F
Compensation is performed such that the resistance r between S and D of the ET decreases and the input voltage Vi of the switching power amplifier circuit 2 decreases.
The resistors R7 and R8 constitute a signal circuit according to the present invention. The adjusting resistor R9 is not limited to a resistor, and may be any so-called impedance element.

Embodiment 3 FIG. FIG. 4 shows a signal circuit of the bias resistors R7 and R8 of the divider 5 of FIG. The characteristic of the function circuit 15 is configured such that the characteristic of the divider 5 becomes the characteristic shown in FIG. By using the function circuit 15, it is possible to obtain a function characteristic of compensating the power supply voltage characteristic of the switching power amplifier circuit 2 more accurately, so that the voltage fluctuation compensation characteristic can be further improved. The function is not limited to the circuit example shown in FIG. 4, and the function may be made smoother by increasing the number of diodes used, or the semiconductor may be configured using another known semiconductor in place of the diode.

Embodiment 4 FIG. 5 shows the A / D converter 10 and the constant table ROM, which are composed of the divider 5 and the function circuit 15 shown in FIG.
11, an electronic volume 12, and a controller 13. By rewriting the contents of the constant table ROM 11, arbitrary function characteristics (switching power amplifier circuit 2
Function characteristic according to the characteristic of the above), thereby enabling more accurate compensation. The controller 13 is used to control these components as a whole. Other parts are the same as those in FIGS.
The power supply voltage is captured by the A / D converter 10 and the compensation level of the gain corresponding to the change in the power supply voltage level is obtained by obtaining the compensation amount from the ROM 11 recorded in advance and controlling the electronic volume 12 with that value. Thus, a high signal reduction rate is obtained. It goes without saying that the portion that cannot be compensated is further compensated by the entire feedback loop including the feedback circuit.

[0026]

As described above, in the high-precision and high-efficiency power amplifier according to the present invention, the power amplifying section is constituted by an efficient switching power amplifying circuit, and an efficient rectifying power supply is used for the power supply. Since the divider for compensating the gain fluctuation of the switching power amplifier due to the voltage fluctuation of the rectified power supply device is used, the effect that the efficiency of the power amplifier as a whole is high can be obtained.

Since the voltage fluctuation of the power supply device is compensated by the divider circuit, there is no need to forcibly increase the gain of the voltage amplifier circuit, and there is an effect that stable operation can be expected.

The divider constituted by using the FET can constitute an accurate division circuit at a low cost. The signal function circuit can easily obtain a characteristic for more accurately compensating the power supply voltage characteristic of the switching power amplifier circuit.

The characteristic table based on the ROM and the divider using the electronic volume can obtain extremely accurate compensation characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a power amplifier according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of characteristics of the power amplifier circuit of FIG. 1;

FIG. 3 is a configuration diagram of a power amplifier according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a power amplifier according to Embodiment 3 of the present invention.

FIG. 5 is a configuration diagram of a power amplifier according to a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional high-precision high-efficiency power amplifier.

FIG. 7 is a characteristic explanatory diagram of FIG. 6;

[Explanation of symbols]

1 voltage amplifier circuit, 2 switching power amplifier circuit, 3 feedback circuit, 4 power supply device, 5 divider, 6 FE
T, 9 adjustment resistor (impedance element), 15 function circuit, 51 high precision power amplifier

Continued on the front page F-term (reference) 5J029 AA10 CA07 EA01 EA04 FA00 5J040 AA02 AA18 AA26 BA01 BB00 BB02 BB07 BC02 CA05 CA33 DA07 EA02 FA00 5J090 AA00 AA01 CA04 CA36 FA08 FN09 HA09 HA25 HN04 KA00 MA11 CA01 FA04 HA09 HA25 KA47 KA51 MA13 SA11 TA02

Claims (5)

[Claims] 1. A voltage amplifying circuit for amplifying an input signal, a switching power amplifying circuit for receiving the output signal of the voltage amplifying circuit and amplifying the power, a power supply for supplying a power supply voltage to the switching power amplifying circuit, and the switching power A power amplifier including a feedback circuit that feedbacks an output signal of an amplifier circuit and adds the output signal to the input signal with a reverse polarity, wherein the power amplifier is inserted between the voltage amplifier circuit and the switching power amplifier circuit, A power amplifier, comprising: a divider that divides an output signal by the power supply voltage supplied to the switching power amplifier circuit and sends a quotient output to an input terminal of the switching power amplifier circuit. 2. The power amplifier according to claim 1, wherein the power supply is a rectified power supply. 3. A divider includes an impedance element connected between an output terminal of the amplifier circuit and an input terminal of the switching power amplifier circuit, and a FET element connected between an input terminal of the switching power amplifier circuit and ground. , This F
The power amplifier according to claim 1, further comprising a signal circuit that sends the power supply voltage to a gate terminal of the ET element. 4. The power amplifier according to claim 3, wherein the signal circuit is a function circuit including a semiconductor device. 5. A divider includes an electronic regulator whose attenuation rate is controlled by a control signal, an A / D converter that converts the power supply voltage into a digital signal, and a control value corresponding to a change in the digital signal. The power amplifier according to claim 1, further comprising: a ROM that stores the stored table; and a controller that selects the control value from the table stored in the ROM and outputs the selected control value to the electronic volume.