JPH0265515A - Level control circuit - Google Patents

Abstract

PURPOSE:To make the efficiency of an amplifier constant by providing an amplifier with variable gain function amplifying an input signal and an automatic level amplifier controlling the gain of the amplifier with variable gain function, and obtaining a reference voltage while dividing a power voltage applied to the amplifier with variable gain function. CONSTITUTION:A signal inputted from a signal input terminal 1 is amplified by a amplifier with variable gain function 4 and outputted from a signal output terminal 2. In such a case, part of the signal is extracted from a level detector 5, rectified and inputted to an automatic level control amplifier 6. Then the voltage is compared with a power voltage divided by resistors 8, 9 to control the gain of the amplifier with variable gain function 4 to make the output level at the signal output terminal 2 constant based on the result of comparison. Thus, the power voltage applied to the power input terminal 3 is varied to change the voltage divided by the resistors 8, 9, a reference voltage in the automatic level control amplifier 6 is changed, and the variable control of the output level is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a level control circuit for a power amplifier used in a radio transmitter or the like.

[Conventional technology]

A conventional level control circuit of this type is shown in FIG.

In the figure, ■ is a signal input terminal, 2 is a signal output terminal, and 3 is a signal input terminal.
4 is a power supply input terminal, 4 is an amplifier with a variable gain function, 5 is a level detector, 6 is an automatic level control amplifier, and 7 is a variable resistor. A signal input from the signal input terminal 1 is amplified by the variable gain amplifier 4 and output from the signal output terminal 2. At this time, a portion of the signal is taken out from the level detector 5, rectified, and compared with the voltage across the variable resistor 7 in the level control amplifier 6. Based on this comparison result, the gain of the variable gain amplifier 4 is controlled to perform level control so that the output level of the signal output terminal 2 is constant.

[Problem to be solved by the invention]

In the conventional level control circuit described above, a constant power supply voltage adjusted by a variable resistor 7 is used as the reference voltage in the automatic level control amplifier 6.
) and (b), even when controlled to different output levels, the saturated output of the amplifier itself remains constant, as shown by the solid lines in each figure. Therefore, the power consumption of the amplifier as a whole remains almost the same, and there is a problem in that the efficiency of the amplifier decreases, especially when the output level is lowered.

The present invention aims to provide a level control circuit that improves the efficiency of an amplifier.

[Means to solve the problem]

The level control circuit of the present invention includes an amplifier with a variable gain function that amplifies an input signal, and an automatic level amplifier that controls the gain of the amplifier with a variable gain function by comparing the amplified output signal with a reference voltage. The voltage is obtained by dividing the power supply voltage applied to the variable gain amplifier.

[Effect]

In the above-mentioned configuration, in order to control the level of the output signal by the automatic level amplifier, the power supply voltage is changed to change the reference voltage. It becomes possible to keep the efficiency constant.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 1 is a signal input terminal, 2 is a signal output terminal, and 3 is 1! 4 is an amplifier with a variable gain function, 5 is an output level detector, and 6 is an automatic level control amplifier. The power supply voltage applied to the power supply input terminal 3 is configured to be able to be changed arbitrarily, and the power supply voltage applied to the power supply input terminal 3 is divided by resistors 8 and 9 and is applied to the automatic level control amplifier. This is the reference voltage supplied to 6.

According to this configuration, a signal input from the signal input terminal 1 is amplified by the variable gain amplifier 4 and output from the signal output terminal 2. At this time, a part of the signal is taken out from the level detector 5, rectified, and input to the automatic level control amplifier 6. In the automatic level control amplifier 6, the voltage is compared with the power supply voltage divided by the resistor 8.9, and based on the comparison result, the variable gain function amplifier 4 is adjusted so that the output level of the signal output terminal 2 is constant. control the gain of.

Therefore, in this level control, by changing the power supply voltage applied to the power supply input terminal 3, the voltage divided by the resistors 8 and 9 is also changed, the reference voltage in the automatic level control amplifier 6 is changed, and the output level It becomes possible to control changes.

Figures 2 (a) and (b) show the input/output characteristics when the output level is varied, where the solid line is the characteristic at maximum gain with the amplifier level control removed, and the broken line is the characteristic when level control is applied. It shows. As mentioned above, since the output level is varied by changing the power supply voltage at the power supply input terminal 3, the output level can be varied based on the voltage divided by the resistor 8゜9, and at the same time the variable gain function is added. amplifier 4
The saturation output also changes as the power supply voltage changes. Therefore, by appropriately selecting the voltage division ratio of the resistors 8 and 9, when the output level is lowered, the saturated output is also lowered and the power supply efficiency can be kept approximately constant.

〔Effect of the invention〕

As explained above, in the present invention, the reference voltage of the automatic level amplifier that controls the gain of the variable gain amplifier is obtained by dividing the power supply voltage applied to the variable gain amplifier. In order to control the level of the output signal, it is sufficient to change the power supply voltage. Simultaneously with this level control, the saturated output of the variable gain amplifier can be controlled, which has the effect of keeping the amplification efficiency approximately constant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of a level control circuit according to the present invention, and FIGS. 2(a) and 2(b) are characteristic diagrams of output signals of different signal levels with respect to input signals of the embodiment of FIG.
Figure 3 is a circuit diagram of a conventional level control circuit, Figure 4 (a)
and (b) are characteristic diagrams of output signals of different signal levels with respect to the input signals of FIG. 3, respectively. 1...Signal input terminal, 2...Signal output terminal, 3...
・Power input terminal, 4... Amplifier with variable gain function, 5.
...Level detector, 6...Automatic level amplifier, 7...
・Variable resistance, 8.9...Resistance. Faction:! AceΔYsa□49ΔZko, -kawaguΔan→ -7pΔ7→

Claims (1)

[Claims] 1. An amplifier with a variable gain function that amplifies an input signal, and an automatic level amplifier that compares the amplified output signal with a reference voltage to control the gain of the amplifier with a variable gain function,
A level control circuit characterized in that the reference voltage is obtained by dividing a power supply voltage applied to the variable gain amplifier.