JPH0918236A - Operating current detection circuit for amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To faithfully detect the variance of an operating current by providing a 1st bypass capacitor showing a high impedance at the load side and a 2nd bypass capacitor showing a low impedance at the power supply side respectively. SOLUTION: A 1st bypass capacitor 6 is provided between the load side of a current detection element 1 and the ground, and a 2nd bypass capacitor 7 is provided between the power supply side of the element 1 and the ground. The impedance of the capacitor 7 is set at a level that is satisfactorily low even to the amplification frequency of the amplification signal input. On the other hand, the impedance of the capacitor 6 is set at a level that is satisfactorily low to the carrier frequency of the amplification signal input and satisfactorily high to the amplitude modulation frequency. As a result, only the amplitude modulation frequency component is supplied to the element 1 by the capacitor 6 among the load currents. Thus it is possible to easily detect the variance of an operating current and to extremely reduce the conditions against the detection sensitivity of the internal impedance of the element 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operating current detecting circuit, and more particularly to an operating current detecting circuit for an amplifier which detects an operating current of an amplifier which amplifies and outputs an amplified signal input of an amplitude modulation wave of an analog amplitude modulation type.

[0002]

2. Description of the Related Art An operating current detection circuit for an amplifier for detecting an operating current of an amplifier for amplifying an amplitude modulation wave of a digital amplitude modulation type or an analog amplitude modulation type is well known.

FIGS. 3 and 4 are configuration diagrams showing a first example and a second example of an operating current detection circuit of an amplifier for an analog amplitude modulation wave, respectively.

The operating current detection circuit of the amplifier shown in FIG.
The current detection element 1, the load 4, the transistor 5 as an amplifier, and the bypass capacitor 8 are provided, and the current detection element 1 receives the amplified signal of the amplitude modulation wave at the transistor 5.
Outputs the operating current detection output.

Further, FIG. 4 is different from FIG. 3 only in that the bypass capacitor 9 is arranged between the power source side of the current detecting element 1 and the ground.
Unlike the above case, the current detection element 1 outputs an operating current detection output.

When the amplified signal input is a digital amplitude modulation wave such as video amplitude modulation, and the modulation amplitude level is connected for a certain period of time, the operating current detection circuit of the amplifier is also substantially the same as for the analog amplitude modulation wave. And
As shown in FIG. 3, the circuit configuration uses only the current detection element 1 and the bypass capacitor 8 for the load 4.

[0007]

In the conventional operating current detection circuit for an amplifier described above, a bypass capacitor 8 is provided between the current detection element 1 and the load 4 shown in FIG. In this case, the capacitance of the bypass capacitor is set to a value that has a sufficient bypass effect even when the operating current changes due to the amplitude modulation component of the signal to be amplified. Therefore, the current detection element 1 has a drawback that it cannot faithfully detect a change in the operating current due to the amplitude modulation component of the amplified signal.

Further, when the operating current detection circuit of FIG. 4 detects the operating current of the amplifier with respect to the analog amplitude modulated wave, the carrier frequency component contained in the amplified signal is also applied to the current detection element 1 and, therefore, There is a drawback that it is necessary to ensure that the internal impedance of the current detection element 1 is sufficiently low and that the detection sensitivity is constant in a wide frequency range from DC to the carrier frequency.

The object of the present invention is to eliminate the above-mentioned drawbacks, and to provide an operational current detection circuit for an amplifier having a simple structure capable of detecting fluctuations in the operational current of the amplifier due to an amplitude modulation component with respect to an analog amplitude modulation wave. Become.

[0010]

SUMMARY OF THE INVENTION An operational current detection circuit for an amplifier according to the present invention is a current detection circuit that is inserted between a load and a power source of an amplifier for amplifying an amplified signal of an analog amplitude modulation type to detect an operating current of the amplifier. The element, which is connected between the load side of the current detection element and the ground, exhibits a sufficiently low impedance with respect to the carrier frequency included in the output of the amplifier, and sufficiently with respect to the amplitude modulation frequency included in the output of the amplifier. A first bypass capacitor whose capacitance is set so as to exhibit high impedance, and a sufficiently low impedance with respect to the amplitude modulation frequency included in the output of the amplifier, which is connected between the power supply side of the current detection element and the ground. And a second bypass capacitor whose capacitance value is set so as to exhibit.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of an operating current detection circuit for an amplifier according to the present invention. The embodiment shown in FIG. 1 is an example of a case of an operating current detection circuit of an amplifier for an analog amplitude modulated wave, and in addition to the current detection element 1, the load 4, the transistor 5 and the load side of the current detection element 1. A first bypass capacitor 6 arranged between the ground and a second bypass capacitor 7 arranged between the power supply side of the current detection element 1 and the ground.
It comprises. It should be noted that the current detection element 1 is used whose impedance is low only at the frequency of the amplitude modulation component, and whose detection sensitivity is sufficiently secured only at the frequency of the amplitude modulation component.

FIG. 2 is a waveform diagram of the main signals in this embodiment of FIG. The operation of this embodiment will be described below with reference to FIG.

The amplified signal input shown in FIG. 2A is input to the transistor 5 as an analog amplitude modulated wave. When the transistor 5 is set to class AB or class B operation, the load current flowing through the load 4 and the transistor 5 becomes as shown in FIG. In FIGS. 2A and 2B, the dotted line indicates the envelope, that is, the amplitude modulation component, and also indicates the carrier frequency in practice.

By the way, if the impedance of the first bypass capacitor 6 is selected to have a sufficiently low value at the carrier frequency of the amplified signal input shown in FIG. 2 (a) and a sufficiently high value at the amplitude modulation frequency, FIG. Of the load current shown in (b), only the amplitude modulation frequency component is supplied to the current detection element 1 from the first bypass capacitor 6. Therefore, the current flowing through the current detection element 1 is
A waveform as shown in (c) is obtained.

The second bypass capacitor 7 shown in FIG.
The impedance is selected so that it will be a sufficiently low value even at the amplification modulation frequency of the amplified signal input of FIG.

In this embodiment, as the amplifier, a transistor amplifier having a grounded emitter is used.
The same can be done with the collector ground circuit.
It is also possible to use an amplifier other than a transistor.

[0018]

As described above, according to the present invention, the bypass capacitor is discharged to the load side and the power source side of the current detecting element inserted between the load of the amplifier of the analog amplitude modulation signal and the power source, and the bypass capacitor of Fukagawa is used. , The impedance of the bypass capacitor on the power supply side is sufficiently low for the amplitude modulation component, and the impedance of the bypass capacitor on the power supply side is sufficiently low. There is an effect that faithful detection of fluctuations in the operating current can be easily performed, and conditions for the internal impedance of the current detection element and the detection sensitivity can be significantly relaxed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an operating current detection circuit of an amplifier according to the present invention.

FIG. 2 is a waveform diagram of main signals in the embodiment of FIG.

FIG. 3 is a configuration diagram showing a first example of an operating current detection circuit of a conventional amplifier.

FIG. 4 is a configuration diagram showing a second example of an operating current detection circuit of a conventional amplifier.

[Explanation of symbols]

 1 Current Detection Element 4 Load 5 Transistor 6 First Bypass Capacitor 7 Second Bypass Capacitor

Claims (1)

[Claims] 1. A current detecting element which is inserted between a load of an amplifier for amplifying an amplified signal input of analog amplitude modulation type and a power source, and which detects an operating current of the amplifier, and between a load side of the current detecting element and earth. A first bypass whose capacitance is set so as to exhibit a sufficiently low impedance with respect to the carrier frequency included in the output of the amplifier and a sufficiently high impedance with respect to the amplitude modulation frequency included in the output of the amplifier. A capacitor and a second bypass capacitor connected between the power supply side of the current detection element and the ground, and having a capacitance value set so as to exhibit an impedance sufficiently low with respect to the amplitude modulation frequency included in the output of the amplifier. An operating current detection circuit for an amplifier characterized by comprising.