JP2003087069A - Automatic power control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic power control circuit capable of solving the problem of heat radiation of a transistor. SOLUTION: A switching power supply 26 is used as a means for generating a control voltage Vb for controlling the amplification factor of a transmission amplifier 21. The power supply 26 generates the voltage Vb according to a transmission power value (transmission output) which is detected by a detecting circuit 24 between both electrodes of a smoothing capacitor 34, by enabling an FET 31 to perform switching operations by a PWM (Pulse Wave Modulation) output of a microcomputer 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic power control circuit.

[0002]

2. Description of the Related Art An automatic power control circuit is often used to control the transmission output of a wireless device. The auto power control circuit is called an APC circuit by taking the English acronym. FIG. 7 shows a conventional APC circuit of a method of detecting transmission power and performing feedback control. In this figure,
Reference numeral 11 is a transmission amplifier that amplifies an input signal (transmission signal). The transmission amplifier 11 is an amplifier composed of a bipolar transistor, and 11a is an output control terminal of the amplifier 11. As shown in a specific circuit example of the transmission amplifier of FIG. 8, when the transmission amplifier 11 is formed of a bipolar transistor, the output control terminal 11a controls the base current and the power supply in the preceding stage of the amplifier group, so that the FET type amplifier control is performed. Unlike that, it requires current capacity.

The low-pass filter 12 connected to the output of the transmission amplifier 11 is for reducing unnecessary radiation of the transmission amplifier 11, and the antenna 13 is connected to the output of the low-pass filter 12. Also, this low-pass filter 1
The transmission power is detected by the detection circuit 14 from the middle of 2. This detection circuit 14 uses a diode rectifier circuit and can obtain a voltage output that is directly proportional to the transmission power level. This voltage output is used as the reference voltage Vref and the differential amplifier 15
And the output corresponding to the difference between the two voltages is obtained from the differential amplifier 15. Then, the output of the differential amplifier 15 is converted into a voltage and current suitable for controlling the output control terminal 11a by an amplifier circuit composed of transistors Q2 and Q1, and the voltage and current are supplied to the output control terminal 11a. The transmission output is controlled to be constant by controlling the amplification factor of the transmission amplifier 11.

[0004]

However, in the above circuit, when the output also becomes the 25 W class transmission amplifier 11, the current flowing through the output control terminal 11a becomes several amperes.
Then, the heat loss W consumed in the transistor Q1 is also W = (Vs−Vb) Ib (where Vs is the emitter voltage of the transistor Q1 and Vb and Ib are the output control terminals 11a).
Voltage and current, that is, the collector voltage and collector current of the transistor Q1) becomes several W, and heat radiation design becomes a problem. That is, a large-sized transistor Q1 is required for heat dissipation, and the heat dissipation fin is fixed with a screw, which increases constraints on the design.

The present invention has been made in view of the above points,
An object of the present invention is to provide an auto power control circuit which can solve the heat radiation problem of a transistor.

[0006]

The automatic power control circuit of the present invention detects the output value of the transmission amplifier and controls the amplification factor of the transmission amplifier in accordance with the detected value to make the transmission output constant. In an automatic power control circuit for controlling, a unit that generates a signal whose pulse width is variable according to the output value and a transistor that performs a switching operation by the signal generated by this unit, and a voltage that corresponds to the pulse width are included. And a switching power supply for generating the output voltage. The output voltage of the switching power supply is supplied to the transmission amplifier to control the transmission output at a constant level.

In a preferred mode, the switching power supply is a FET whose gate is supplied with the signal generated by the means, a DC power supply connected to the source of the FET, and a rectifying diode connected to the drain of the FET. And a smoothing capacitor connected to the output of this rectifying diode, and the voltage across the smoothing capacitor is supplied to the transmission amplifier. When the output value of the transmission amplifier increases, the pulse width of the signal decreases, and when the output value of the transmission amplifier decreases, the pulse width of the signal increases.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an APC circuit according to the present invention will be described in detail with reference to the accompanying drawings. Figure 1
FIG. 3 is a circuit diagram showing an embodiment of an APC circuit of the present invention. In this figure, reference numeral 21 is a transmission amplifier that amplifies an input signal (transmission signal). This transmission amplifier 21 is an amplifier composed of bipolar transistors,
Is an output control terminal of the amplifier 21. As shown in the specific circuit example of the transmission amplifier of FIG. 8, when the transmission amplifier 21 is formed of a bipolar transistor, the output control terminal 21a controls the base current and the power supply in the preceding stage of the amplifier group, and therefore the FET type amplifier is used. Unlike control, current capacity is required.

Reference numeral 22 is a low-pass filter connected to the output of the transmission amplifier 21. The low-pass filter 22 is for reducing unnecessary radiation of the transmission amplifier 21, and the antenna 23 is connected to the output of the low-pass filter 22. Further, the transmission power is detected by the detection circuit 24 in the middle of the low-pass filter 22. This detection circuit 2
A diode rectifier circuit 4 is used to obtain a voltage output that is directly proportional to the transmission power level (transmission output).

Voltage output of the detection circuit 24 (detection transmission output)
Is input to the A / D converter of the microcomputer 25 and converted into a digital value. The microcomputer 25 digitally processes this value and generates a PWM output corresponding to the A / D converter input (transmission output) from the PWM port built in the microcomputer.

PWM (Pulse Width Mod)
output) is shown in FIG. The PWM output is a signal whose period is constant and whose pulse width (“H” period) is varied according to the A / D converter input (transmission output). Here, the A / D converter input (transmission output) is The pulse width is set to be short when the value is large and to be long when the A / D converter input (transmission output) is small.

Returning to FIG. 1, 26 is a switching power supply, which is an FET 31, a DC power supply 32, and a rectifying diode 3.
3 and a smoothing capacitor 34. FET3
1, the gate is connected to the PWM output of the microcomputer 25. The positive pole of the DC power source 32 is connected to the source of the FET 31, and the negative pole is grounded. Rectifying diode 33
Has an anode connected to the drain of the FET 31. The smoothing capacitor 34 is connected between the cathode of the rectifying diode 33 and the ground. The switching power supply 26 has a control voltage Vb corresponding to the transmission power value (transmission output) detected by the detection circuit 24 when the FET 31 performs a switching operation by the PWM output of the microcomputer 25.
Is generated across the smoothing capacitor 34. Then, the control voltage Vb is supplied to the output control terminal 21a of the transmission amplifier 21 to control the amplification factor of the transmission amplifier 21 so that the transmission output is controlled to be constant.

Microcomputer 25 and switching power supply 26
This operation is shown in detail in FIG. The control voltage Vb required to obtain the target transmission output is the same as in the conventional circuit of FIG. The pulse width (duty ratio) of the PWM output required to obtain the control voltage Vb suitable for the target transmission output is also uniquely determined.

As shown in FIG. 3B, when the transmission output is the target value and there is no fluctuation, the output of the detection circuit 24 (A / D converter input) is also constant, so that the microcomputer 25 outputs the PW.
The pulse width of the M output is kept constant. As a result, the control voltage Vb of the switching power supply 26 also becomes constant.

On the other hand, when the transmission output rises from the target value as shown in FIG. 3 (a), the A / D converter input also rises. In this case, the microcomputer 25 operates so as to reduce the pulse width of the PWM output. Then, the output of the switching power supply 26 drops, and the control voltage Vb is lowered to act to lower the transmission output to the target value.

On the contrary, when the transmission output drops from the target value as shown in FIG. 3C, the input of the A / D converter drops. In this case, the microcomputer 25 operates so as to increase the pulse width of the PWM output. Therefore, the output of the switching power supply 26 rises, the control voltage Vb rises,
Increase the transmission output to the target value.

As described above, according to the above circuit, the transmission output is controlled to be constant by using the microcomputer 25 and the switching power supply 26.

The details of the microcomputer 25 are shown in FIG. The microcomputer 25 is provided with an A / D converter 41, a calculation means 42, a storage means 43, and a PWM waveform output means 44. In the storage means 43, the A / D converter output pair PWM is stored in advance.
The output relationship of the output pulse width is stored.

In the microcomputer 25 thus constructed, the output of the detection circuit 24 shown in FIG. 1 is the A / D converter 4
It is converted into a digital value by 1. Then, according to the output of the A / D converter 41, the PWM output pulse width control signal is calculated according to the output relationship of the A / D converter output and the PWM output pulse width stored in the storage means 43 in advance.
2 to the PWM waveform output means 44. Then,
The PWM waveform output means 44 outputs a PWM output having a pulse width according to the supplied PWM output pulse width control signal, that is, according to the input (transmission output) of the A / D converter 41.

FIG. 5 is a diagram showing numerically the output relationship between the A / D converter 41 input (output) and the PWM output pulse width in the microcomputer 25 as described above. As described above, the PWM output pulse width is variable according to the A / D converter input (transmission output), and the PWM output pulse width becomes shorter as the A / D converter input (transmission output) increases. On the contrary, if the A / D converter input (transmission output) decreases, the PWM output pulse width becomes longer.

FIG. 6 is a flowchart showing the operation of the microcomputer 25 as described above. The microcomputer 25 A / D-converts the transmission power (transmission output) detection value in step S1.
Then, step S2 of controlling the PWM output pulse width according to the A / D conversion output obtained in step S1 and step S3 of generating the PWM output with the pulse width controlled in step S2 are repeated.

In the above APC circuit, the switching power supply 2 is used to generate the control voltage Vb.
6 is used, the heat loss in the transistor (FET 31) is significantly improved, the heat radiation problem of the transistor can be solved, the transistor can be miniaturized, and the cost can be reduced by deleting the parts necessary for heat radiation.

Although the FET 31 is used as the transistor of the switching power supply 26 in the above embodiment, it may be replaced with a bipolar transistor.

[0024]

As described in detail above, according to the auto power control circuit of the present invention, the heat radiation problem of the transistor can be solved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an APC circuit according to the present invention.

FIG. 2 is a waveform diagram showing a PWM output according to the embodiment of the present invention.

FIG. 3 is a diagram showing in detail operations of a microcomputer and a switching power supply according to the embodiment of the present invention.

FIG. 4 is a circuit diagram showing details of a microcomputer according to the embodiment of the present invention.

FIG. 5 is an A / D of the microcomputer according to the embodiment of the present invention.
The figure which shows the output relationship of converter input (output) vs. PWM output pulse width by a numerical example.

FIG. 6 is a flowchart showing the operation of the microcomputer according to the embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional APC circuit.

FIG. 8 is a circuit diagram showing a specific circuit example of a transmission amplifier.

[Explanation of symbols]

21 Transmitter amplifier 22 Low-pass filter 23 antenna 24 Detection circuit 25 microcomputer 26 Switching power supply 31 FET 32 DC power supply 33 Rectifier diode 34 Smoothing capacitor

Claims (3)

[Claims] 1. An automatic power control circuit for controlling a transmission output constant by detecting an output value of a transmission amplifier and controlling an amplification factor of the transmission amplifier according to the detected value. And a switching power supply for generating a voltage according to the pulse width, the switching power supply having a transistor for performing a switching operation according to the signal generated by the means, Is supplied to the transmission amplifier to control the transmission output at a constant level. 2. The switching power supply includes an FET whose gate is supplied with the signal generated by the means, and an FE
It comprises a DC power source connected to the source of T, a rectifying diode connected to the drain of the FET, and a smoothing capacitor connected to the output of the rectifying diode, and the voltage across the smoothing capacitor is the transmission voltage. The auto power control circuit according to claim 1, wherein the auto power control circuit is supplied to an amplifier. 3. The pulse width of the signal decreases as the output value of the transmission amplifier increases, and the pulse width of the signal increases as the output value of the transmission amplifier decreases. Auto power control circuit described in.