JPH11186863A - Alc circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influence from a load and to enlarge a frequency band by providing a power divider for branching output into two, an amplifier for the amplification of one of output signals and the amplifier for feeding back and outputting the other output signal. SOLUTION: To the conventional constitution of a variable attenuator 20, a detector 50 and an integrator 60, the power divider 30 and the amplifiers 41 and 42 are added. The power divider 30 divides signal power by providing the impedance matching of input and output. For instance, in the case of using the three resistors of 16.6 Ω, the power divider of impedance 50 Ω and an attenuation amount 6dB is attained. The amplifiers 41 and 42 are provided with isolation characteristics for amplifying signals in a forward direction and attenuating the signals in an opposite direction. Since the isolation of feedback signals and reflection signals is enlarged, the influence from the load is reduced. Also, in the case of using the power divider for the branching of the signals, the frequency band is widened as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ALC circuit for automatically controlling the output of a signal source to a constant level.

[0002]

2. Description of the Related Art An example of the prior art will be described with reference to FIGS. As shown in FIG. 5, the conventional ALC circuit includes a variable attenuator 20, a detector 50, an integrator 6
0. The output of the signal source 10 is automatically controlled to a constant level and output to the load 90.

The variable attenuator 20 is an attenuator whose attenuation can be varied by a control signal. Detector 50
Detects the high-frequency signal of the signal source 10 and outputs a voltage proportional to the level of the signal source. The integrator 60 includes the detector 50
Are integrated to determine the response characteristics of a signal that is fed back as a control signal for the variable attenuator 20.

In the ALC circuit shown in FIG. 5, if the impedance of the load 90 matches the output impedance of the ALC circuit and is constant, a reflected signal S2 from the load 90 for the output signal S1 is not generated. The feedback loop of the ALC circuit operates effectively.

However, when the impedance of the load 90 is AL
If the output impedance does not match the output impedance of the C circuit or the impedance of the load 90 fluctuates, the reflected signal S2 from the load 90 with respect to the output signal S1
Occurs. In this case, the reflected signal S2 from the load 90
Is superimposed on the feedback signal S3 of the ALC circuit, so that the output level of the signal source cannot be accurately and stably controlled.

For example, assuming that the output level of the variable attenuator 20 is 0 dBm, the level of the output signal S1 of the load 90 is also 0 dBm. Then, the impedance of the load 90 fluctuates, and the reflection of power from the load 90 becomes 1/10.
Assuming that there is 0, the output level is −20 dBm from −0 dBm.
An attenuated -20 dBm reflected signal S2 is generated from the load 90. In this case, the reflected signal S2 generated from the load 90
Directly affects the detector 50.

On the other hand, the feedback signal S of the ALC circuit
The level of 3 indicates that the output level of the variable attenuator 20 is 0
0 dB at the input of the detector 50
m.

Therefore, the magnitude of the influence of the fluctuation of the load 90 can be expressed as a difference between the feedback signal S3 and the reflected signal S2 at the input section of the detector 50, that is, as an isolation, and the value is a very good value of 20 dB. is not.

Therefore, as shown in FIG. 6, an ALC circuit in which a directional coupler 70 is added to the output of the variable attenuator 20 is used. In this ALC circuit, the directional coupler 70 converts a signal from the variable attenuator 20 into a detector 5
0, the reflected signal S2 from the load 90 has less influence on the detector 50 due to the isolation of the directional coupler 70.

However, the isolation of the directional coupler 70 is not so large, and the frequency band is not wide.
For example, as an example of the characteristics of the directional coupler 70, the frequency band is about 2 decades from 10 MHz to 2 GHz, and the isolation is 10 dB.

Next, the operation will be described using specific numerical examples. The output level of the variable attenuator 20 is set to 0 dBm. Further, the insertion loss of the directional coupler 70 is 0.5 dB, the coupling is -10 dB, and the directional coupling is -20 dB.
B. The isolation of the directional coupler 70 is a difference of 10 dB between the coupling and the directional coupling.

At this time, the level of the output signal S1 of the ALC circuit at the load 90 is -0.5 dBm because the insertion loss of the directional coupler 70 is 0.5 dB.

If the impedance of the load 90 fluctuates and the power reflected from the load 90 is 1/100, the reflected signal S2 of -20.5 dBm attenuated by 20 dB from the output level -0.5 dBm is output. From 90.

The level of the reflected signal S 2 from the load 90 is determined by the directional coupler 70 at the input of the detector 50.
Further, the attenuation is further reduced by 20 dB to -40.5 dBm.

On the other hand, in the feedback loop of the ALC circuit, the level of the feedback signal S3 is attenuated by 10 dB from the output level of 0 dBm of the variable attenuator 20 by the directional coupling of the directional coupler 70, and at the input of the detector 50. -10 dBm.

Therefore, as shown in FIG. 4, the feedback signal S3 and the reflected signal S2 at the input of the detector 50 are provided.
Is 30.5 dB.

That is, by using the directional coupler 70 in the ALC circuit, the isolation between the feedback signal S3 and the reflected signal S2 at the input of the detector 50 is improved, but the frequency band is directionally coupled. Limiter to a few octaves.

[0018]

As described above, the conventional ALC circuit is susceptible to fluctuations in the impedance of the load, and the isolation is improved when a directional coupler is used. Has become narrow and there is practical inconvenience. Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide an ALC circuit which is less affected by a load and can have a wide frequency band.

[0019]

That is, a first aspect of the present invention, which has been made to achieve the above object, is to provide an ALC circuit for automatically controlling an output signal level of a signal source to be constant, and to provide a power divider for bifurcating an output. A first amplifier for amplifying one output signal of the power divider and outputting the amplified signal to a load;
A second amplifier that amplifies the other output signal of the power divider and outputs the amplified signal as feedback is provided.

A second aspect of the present invention, which has been made to achieve the above object, is to provide a variable attenuator capable of receiving an output of a signal source and changing an amount of attenuation by a control signal, and bifurcating the output of the variable attenuator. A power divider, a first amplifier for amplifying one output signal of the power divider and outputting the amplified signal to a load, a second amplifier for amplifying and outputting the other output signal of the power divider, and a second amplifier for amplifying the other output signal of the power divider. An ALC circuit comprising: a detector that detects an output signal of an amplifier; and an integrator that integrates a detection signal of the detector and outputs a control signal of the variable attenuator. .

A third aspect of the present invention, which has been made to achieve the above object, is an ALC circuit in which the power divider according to the first or second aspect of the present invention is replaced with a directional coupler.

Further, a fourth aspect of the present invention, which has been made to achieve the above object, has a gist of an ALC circuit in which the power divider according to the first or second aspect of the present invention is replaced with a resistor coupler.

A fifth aspect of the present invention, which has been made to achieve the above object, is that the first amplifier and the second amplifier have the same gain characteristics as the first and second amplifiers of the present invention.
The gist is the ALC circuit described in 2, 3, or 4.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in the following examples.

[0025]

(Embodiment 1) Embodiment 1 of the present invention will be described with reference to FIGS. As shown in FIG. 1, the ALC circuit of the present invention has a configuration in which a power divider 30, an amplifier 41, and an amplifier 42 are added to the conventional configuration of the variable attenuator 20, the detector 50, and the integrator 60. Has become. Then, the output from the signal source 10 is automatically controlled to a constant level and output to the load 90.

The description of the operations of the variable attenuator 20, the detector 50, and the integrator 60, which are the same as in the conventional configuration, will be omitted.

The power divider 30 can distribute signal power by providing input and output impedance matching. For example, when three 16.6 Ω resistors are used, the power divider has an impedance of 50 Ω and an attenuation of 6 dB.

The amplifier 41 and the amplifier 42 have an isolation characteristic of amplifying a signal in the forward direction and attenuating a signal in the opposite direction. Here, the reason why the two amplifiers 41 and 42 are used is to improve gain tracking due to a temperature change.

Therefore, two amplifiers 41 and 4
It is desirable that the tracking characteristic of the gain due to the temperature change in the frequency band to be used matches 2.

Next, the operation will be described using specific numerical examples. The output level of the variable attenuator 20 is set to 0 dBm. The forward gain characteristic of the amplifier 41 is +10 dB.
And the isolation is -20 dB.

At this time, the input level of the amplifier 41 becomes -6 dBm by the power divider. In addition, amplifier 4
The level of the output signal S1 at the output of 1 has a gain of 1
Since there is 0 dB, it becomes +4 dBm.

Here, assuming that the impedance of the load 90 fluctuates and the power reflected from the load 90 is 1/100, the load 90 generates a reflected signal S2 of -16 dBm attenuated by 20 dB from the output level +4 dBm.

The level of the reflected signal S2 from the load 90 is
-20dB due to the isolation of amplifier 41
It attenuates to -36 dBm. Further, the level of the reflected signal S2 is attenuated by -6 dB in the power divider 30 and amplified by 20 dB in the amplifier 42, so that the output of the amplifier 42 becomes -32dBm.

On the other hand, the level of the feedback signal S3 is attenuated by -6 dB in the power divider 30 from 0 dBm of the output level of the variable attenuator 20, and
Is amplified by 10 dB, so that the output of the amplifier 42 becomes +4 dBm.

Therefore, as shown in FIG. 4, the isolation between the feedback signal 2 and the reflected signal 3 at the input of the detector 50 is 36 dB. Since the isolation of the ALC circuit using the conventional directional coupler is 30.5 dB, the improvement is 5.5 dB.

The frequency band of the ALC circuit according to the first embodiment is, for example, 100 kHz since the frequency band of the power divider 30 and the amplifiers 42 and 42 can be easily widened.
The range is 4 decades from z to 1 GHz. Since the frequency band of the ALC circuit using the conventional directional coupler is about 2 decades, the improvement is about 2 times.

In the first embodiment, a circuit diagram is shown in principle for the sake of simplicity of explanation. However, for example, a circuit configuration in which an amplifier is added after the variable attenuator 20 can be similarly implemented.

(Embodiment 2) Embodiment 2 of the present invention is an example in which the power divider 30 of Embodiment 1 is replaced with a directional coupler 70 as shown in FIG.

In this case, the frequency band is limited by the directional coupler 70, but the isolation is further improved by the directional coupler 70 compared to the first embodiment.

(Embodiment 3) Embodiment 2 of the present invention is an example in which the power divider 30 of Embodiment 1 is replaced with a resistor coupler 80 as shown in FIG. The resistor coupler 80 is a signal distributor that extracts a feedback signal by a resistor R.
For example, the resistance R is 200 ohms.

In this case, since the matching between the input and output is not performed, the accuracy of the gain control is not good.
Since the attenuation level of the output level becomes smaller, the gains of the amplifiers 41 and 42 can be reduced and the output level can be increased.

[0042]

The ALC circuit of the present invention is embodied in the form described above, and has the following effects. That is, since the isolation between the feedback signal and the reflected signal is increased, the influence from the load can be reduced. Further, when a power divider is used for branching a signal, the frequency band can be widened. When a directional coupler is used for signal branching, the isolation can be further increased, so that the influence from the load can be further reduced. Further, when a resistive coupler is used for branching a signal, the output level can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ALC circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of Embodiment 2 of the ALC circuit of the present invention.

FIG. 3 is a block diagram of an ALC circuit according to a third embodiment of the present invention.

FIG. 4 is an isolation characteristic diagram of the ALC circuit according to the first embodiment of the present invention and an ALC circuit using a conventional directional coupler.

FIG. 5 is a block diagram of a conventional ALC circuit.

FIG. 6 is a block diagram of an ALC circuit using a conventional directional coupler.

[Explanation of symbols]

 Reference Signs List 10 signal source 20 variable attenuator 30 power divider 41, 42 amplifier 50 detector 60 integrator 70 directional coupler 80 resistive coupler 90 load

Claims (5)

[Claims] An ALC circuit for automatically controlling an output signal level of a signal source to be constant, a power divider for branching an output into two, and a first amplifier for amplifying one output signal of the power divider and outputting the amplified signal to a load. An ALC circuit, comprising: a second amplifier that amplifies the other output signal of the power divider and outputs the amplified signal as feedback. 2. A variable attenuator capable of changing an amount of attenuation by a control signal in response to an output of a signal source, a power divider for branching the output of the variable attenuator into two, and amplifying one output signal of the power divider. A first amplifier that outputs to a load, a second amplifier that amplifies and outputs the other output signal of the power divider, a detector that detects an output signal of the second amplifier, and a detector of the detector An ALC circuit, comprising: an integrator that integrates a signal and outputs a control signal of the variable attenuator. 3. An ALC circuit in which the power divider according to claim 1 is replaced by a directional coupler. 4. An ALC circuit in which the power divider according to claim 1 is replaced with a resistor coupler. 5. The AL according to claim 1, wherein the first amplifier and the second amplifier have the same gain characteristic.
C circuit.