JPH0416074A - Operating current detection circuit for amplifier - Google Patents

Abstract

PURPOSE:To easily detect the operating current including a deviation from an initial setting value by extracting only an amplitude modulation component from an output of a current detection element inserted to an output current circuit of an amplifier of a digital amplitude modulation signal and sampling- and-holding the component in an external timing pulse so as to form an operating current detection output. CONSTITUTION:The operation of a transistor(TR) 5 is set to be a class AB or B operation. An LPF 2 passes through an amplitude modulation component of an input signal, that is, a frequency component of a video signal and blocks the passing of a carrier frequency component and gives the result to a sample- and-hold circuit 3. The sample-and-hold circuit 3 samples the signal by using a timing signal using a horizontal synchronizing signal and holds the sampled value for a period when no horizontal synchronizing signal is absent to send a sample-and-hold output. The sample-and-hold output waveform represents an amplitude modulation component of an amplified signal, that is, an operating current of the amplifier for a horizontal synchronizing period independently of the change in the video signal. Then a change in the operating current due to ambient temperature or the like is easily detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an operating current detection circuit for an amplifier, and particularly to an amplified signal input in a digital amplitude modulation format such as a video amplitude modulation signal or an amplitude modulated wave in an analog amplitude modulation format. The present invention relates to an operating current detection circuit for an amplifier that detects the operating current of an amplifier that amplifies and outputs an amplified signal input.

[Conventional technology]

An amplifier operating current detection circuit that detects the operating current of an amplifier that amplifies an amplitude modulated wave in a digital amplitude modulation format or an analog amplitude modulation format is well known.

FIG. 5 and FIG. 6 are configuration diagrams showing a first example and a second example of an amplifier operating current detection circuit for analog amplitude modulated waves, respectively.

The amplifier operating current detection circuit shown in FIG. 5 includes a current detection element 1, a load 4, a transistor 5 as an amplifier,
A bypass capacitor 8 is provided, and the transistor 5 receives an amplified signal of an amplitude modulated wave and outputs an operating current product from the current detection element 2.

6 differs from the case in FIG. 5 only in that a bypass capacitor 9 is placed between the power supply side of the current detection element 1 and the earth, and the operating current detection output is output from the current detection element 1. Ru.

When the amplified signal input is a digital amplitude modulated wave such as video amplitude modulation, and the modulated amplitude level continues for a certain period of time, the operating current detection circuit of the amplifier is almost the same as that for analog amplitude modulated waves, As shown in Section 5, the circuit configuration was such that only the current detection element 1 and the bypass capacitor 8 for the load 4 were used.

[Problem to be solved by the invention]

In the conventional amplifier operating current detection circuit described above, a bypass capacitor 8 is disposed between the current detection element 1 and the load 4 shown in FIG. 5, and when analog amplitude modulation is targeted, The capacitance of this bypass capacitor is set to a value that provides a sufficient bypass effect even against changes in operating current due to amplitude modulation components of the signal to be amplified. Therefore, the current detection element 1 has a drawback in that it cannot faithfully detect changes in the operating current due to the amplitude modulation component of the amplified signal.

Furthermore, when detecting an operating current using a digital amplitude modulated wave with the circuit configuration shown in FIG. This value varies depending on the degree of amplitude modulation of the amplified signal input to the transistor 5, which is an amplifier. Therefore, although it can be determined that the amplifier is operating, there is a drawback that it is not possible to detect deviations in the operating current value of the amplifier from the initial setting value due to changes in the operating environment temperature or amplified signal input.

Furthermore, when the operating current detection circuit of FIG. 6 detects the operating current of an amplifier with respect to an analog amplitude modulated wave, the carrier frequency component included in the amplified signal is also applied to the current detection element 1, and therefore the DC There is a drawback that it is necessary to ensure that the internal impedance of the current detection element 2 is sufficiently low and the detection sensitivity is constant in a wide frequency range from the carrier frequency to the carrier frequency.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to detect the operating current for digital amplitude modulation regardless of changes in the digital amplitude modulation wave, and for analog amplitude modulation waves to detect the operating current by using an amplifier based on the amplitude modulation component. To provide an operating current detection circuit for an amplifier, which has a simple configuration and is capable of detecting fluctuations in the operating current of an amplifier.

[Means to solve the problem]

An operating current detection circuit for an amplifier according to the present invention includes a current detection element that is inserted between a load of an amplifier that amplifies an amplified signal input in a digital amplitude modulation format and a power supply and detects the operating current of the amplifier, and a current detection element that detects the operating current of the amplifier. A low pass filter removes the carrier wave component from the detected output and extracts the amplitude modulation component, and the output of the low pass filter is supplied from the outside and is sampled during the input period of a timing pulse synchronized with the amplified signal input. The period includes a sample and hold circuit that holds the sample value and outputs the operating current detection output.

Further, the operating current detection circuit for an amplifier of the present invention includes a current detection element that is inserted between a load and a power supply of an amplifier that amplifies an amplified signal input in an analog amplitude modulation format and detects the operating current of the amplifier, and the current detection element. is connected between the load side of the amplifier and the earth, and is arranged so that it exhibits a sufficiently low impedance for the carrier frequency included in the output of the amplifier and a sufficiently high impedance for the amplitude modulation frequency included in the output of the amplifier. A first bypass capacitor having a set capacitance is connected between the power supply side of the current detection element and the earth, and the capacitance value is set so as to exhibit a sufficiently low impedance for the amplitude modulation frequency included in the output of the amplifier. and a second bypass capacitor.

〔Example〕

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

FIG. 1 is a block diagram of a first embodiment of an operating current detection circuit for an amplifier according to the present invention. The embodiment shown in FIG. 1 takes as an example the case where the operating current of an amplifier is detected using a video amplitude modulated signal as a digital amplitude modulated wave, and the carrier wave component is removed from the current detection element 1 and the detected pressure of the current detection element. A low-pass filter (LP) that extracts only low-frequency amplitude modulation components.
F) 2 and a timing pulse supplied from the outside; in this example, the output of LPF2 is sampled during the period when the horizontal synchronization signal is received, and during other periods, this sampled value is held and used as the operating current detection output. It comprises a hold circuit 3, and the same load 4 and transistor 5 as in the conventional example shown in FIG. 5.6. In the embodiment shown in FIG. 1, descriptions of the bias circuit and other contents not directly related to the explanation are omitted.

FIG. 2 is a waveform diagram of main signals in the embodiment of FIG. 1. Hereinafter, the operation of the first embodiment shown in FIG. 1 will be explained with reference to FIG. 2.

An amplified signal input of a video amplitude modulated signal as a digital amplitude modulated wave shown in FIG. 2(a) is input to the transistor 5, which is an amplifier. Assuming that transistor 5 is set to class AB or class B operation, transistor 5,
An operating current waveform shown in FIG. 2(b) is conducted through the load 4 and the current detection element 1. The dotted lines shown in FIGS. 2<a> and 2(b) indicate the envelope of the waveform, which is the amplitude modulation component.

The output of the current detection element 1 having the operating current waveform shown in 27th (b) is input to the LPF 2. The LPF 2 passes the amplitude modulation component of the input signal, that is, the frequency of the video signal, blocks the carrier frequency component, and supplies an output having a low-pass filter pressure waveform shown in FIG. 2(c) to the sample-hold circuit 3. do.

The sample and hold circuit 3 responds to this input as shown in Fig. 2 (d
), sampling is performed using a timing signal that uses the horizontal synchronization signal, and during the period when the horizontal synchronization signal is absent, a sample hold is performed to hold this sampling value, and the second
The sample and hold output shown in Figure (e) is sent out. This sample-and-hold output waveform indicates the amplitude modulation component of the amplified signal, that is, the operating current value of the amplifier during the horizontal synchronization period, which is unrelated to changes in the video signal. Therefore, it becomes possible to easily detect changes in the operating current value due to ambient temperature or the like.

In the first embodiment shown in Fig. 1, the collector operating current of the emitter-grounded transistor amplifier is detected, but it can be similarly performed with the collector-grounded or base-grounded, and the base current and emitter current can also be detected in the same way. It is obvious that this can be done, and furthermore, it is also possible to use amplifying elements other than transistors.

Furthermore, regarding the amplified signal input, in addition to the video signal,
A digital amplitude modulation signal whose amplitude modulation is constant for a certain period of time is possible. For example, Q A M (Q
uadrature Aa+pl 1tude Mod
ulation) signal, the amplitude modulation waveform is constant at the synchronization code position, so this is possible by using the synchronization signal position signal as a timing signal input.

Note that by adding a function to suppress the detection of the carrier wave component of the operating current to the current detection element 1 itself shown in FIG.
It is also clear that a configuration that is equivalently integrated with F2 can be easily implemented.

The third section is a configuration diagram of a second embodiment of the operating current detection circuit for an amplifier according to the present invention. The second embodiment shown in Section 3 takes as an example the case of an operating current detection circuit for an amplifier that targets analog amplitude modulated waves, and includes the current detection element 1, load 4, transistor 5, and other components shown in FIG. , a first bypass capacitor 6 disposed between the load side of the current detection element 1 and the ground, and a second bypass capacitor 7 disposed between the power supply side of the current detection element 1 and the ground. Note that the current detection element 1 used has an impedance that is low only at the frequency of the amplitude modulation component, and a detection sensitivity that is sufficiently ensured only at the frequency of the amplitude modulation component.

FIG. 4 is a waveform diagram of main signals in the second embodiment of FIG. 3. The operation of the second embodiment will be described below with reference to FIG.

The transistor 5 has a fourth wave as an analog amplitude modulated wave.
The amplified signal input shown in Figure (a) is input. When transistor 5 is set to class AB or class B operation, the load current flowing through load 4 and transistor 5 is as shown in Fig. 4 (
b). In FIGS. 4(a) and 4(b), the dotted line indicates the envelope line, that is, the amplitude modulation component, and the solid line indicates the carrier frequency.

By the way, if the impedance of the first bypass capacitor 6 is selected so as to have a sufficiently low value at the carrier wave frequency of the amplified signal input shown in FIG. 4(a) and a sufficiently high value at the amplitude modulation frequency.

Only the amplitude modulation frequency component of the load current shown in FIG. 4(b) is supplied from the first bypass capacitor 6 to the current detection element l. Therefore, the current detection element l
As shown in FIG. 4(c), the current flowing in is only the amplitude modulation component of the amplified signal. Therefore, the output of the current detection element 1 also has a waveform as shown in FIG. 4(c).

The impedance of the second bypass capacitor 7 shown in FIG. 4 is selected so as to have a sufficiently low value even at the amplification modulation frequency of the amplified signal input shown in FIG. 4(a).

In the second embodiment, a common emitter transistor amplifier is used as the amplifier, but a common base or common collector circuit can also be used. Furthermore, it is also possible to use something other than a transistor for the amplifier.

〔Effect of the invention〕

As explained above, the present invention extracts only the amplitude modulation component from the output of a current detection element inserted into the output current circuit of an amplifier for a digital amplitude modulation signal, samples and holds it using an external timing pulse, and generates an operating current detection circuit. This has the effect that the operating current including deviation from the initial setting value can be easily detected regardless of changes in the amplified signal input.

In addition, bypass capacitors are installed on the load side and power supply side of the current detection element inserted between the load of the analog amplitude modulation signal amplifier and the power supply, and the impedance of the bypass capacitor on the load side is set to be sufficient for the amplitude modulation component. By setting the impedance of the bypass capacitor on the power supply side to be high enough for the amplitude modulation component and sufficiently low for the carrier wave component, the impedance of the bypass capacitor on the power supply side can be set to be low enough for the amplitude modulation component to faithfully detect operating current fluctuations due to the amplitude modulation component. This can be easily carried out, and has the effect of significantly relaxing the conditions for the internal impedance and detection sensitivity of the eight current product elements.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the 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. 1, and FIG. 3 is an operation of the amplifier according to the present invention. A configuration diagram of a second embodiment of the current detection circuit, FIG. 4 is a waveform diagram of main signals in the embodiment of FIG. 3, and FIGS. - It is a block diagram which shows an example and a second example. 1... Current detection element, 2... Low pass filter, 3
- Sample and hold circuit, 4... Load, 5... Transistor, 6... First bypass capacitor, 7...
- Second bypass capacitor, 8, 9... bypass capacitor.

Claims (1)

[Scope of Claims] 1. A current detection element that is inserted between the load and power supply of an amplifier that receives an amplified signal input in the digital amplitude modulation format and detects the operating current of the amplification, and a carrier wave from the detection output of the electric detection element. A low-pass filter that removes the amplitude modulation component and extracts the amplitude modulation component, and the output of the low-pass filter is supplied from the outside and is sampled during the input period of a timing pulse synchronized with the input of the pre-amplified signal, and the sampled value is used during other periods. 1. An operating current detection circuit for an amplification, comprising: a sample and hold circuit that holds the current and outputs the operating current. 2. A current detection element that is inserted between the load of an amplifier that increases the input of an analog amplitude modulation type amplified signal and a power supply and detects the operating current of the amplifier, and a current detection element that is connected between the load side of the current detection element and the ground and connected to the amplifier. a first bypass capacitor whose capacitance is set so as to exhibit a sufficiently low impedance for the carrier frequency included in the output of the amplifier and a sufficiently high impedance for the amplitude modulation frequency included in the output of the amplifier; A second bypass capacitor connected between the power supply side of the current detection element and the earth and having a capacitance value set so as to exhibit a sufficiently low impedance for the amplitude modulation frequency included in the output of the amplifier. An amplifier operating current detection circuit characterized by: