JP2002280848A - Input level indication circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an input level indication circuit that can accurately indicate the input level of a signal of its own channel (D wave) even when a disturbing wave (U wave) exists in an adjacent channel and reduces an error in an AGC voltage so as to keep an output level within a prescribed rated value. SOLUTION: The input level indication circuit is provided with a band limit filter eliminating a required wave and extracting only an unwanted wave and placed at an input terminal side, and a differential amplifier that compares the detection voltage of the unwanted wave which has passed through the filter with the detection voltage of a required wave which has passed through a band pass filter to extract the required wave from an output of an AGC circuit so that, when the unwanted wave voltage is greater than the required wave voltage by a prescribed voltage or over, a transistor is shifted from a cut-off state into an active state and the effect of the wave is reduced to obtain an accurate meter indication value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input level display circuit such as a microwave transmission device for transmitting digital signals.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional input level display circuit. This circuit partially uses an AGC circuit for making the fluctuation of the input level constant at the output. Its behavior is
When a high-frequency signal is input from the input terminal 1, a required wave (hereinafter, referred to as D wave) is selected by a bandpass filter (hereinafter, referred to as BPF) 4, and a DC voltage V1 corresponding to the input level is obtained by a detector 5. . V1 is amplified by the differential amplifier 6, and the output level is kept constant by controlling the bias of the gain controller 2, and is output from the output terminal 3. That is, as the input signal level increases, V1 also increases and the output of the differential amplifier 6 decreases. However, when a pin diode attenuator is used for the gain controller 2, for example, the attenuation increases and the output level decreases. As a result, the output level of the output terminal 3 is kept constant.

An input level display 10 displays the level of an input signal using the control voltage.

However, in the conventional circuit, when there is no signal in the used channel and the signal U wave exists in the adjacent channel, the BPF 4 leaks because the frequencies are close to each other. If this leak occurs, the output level becomes approximately the rated output level by the AGC, and the corresponding DC voltage V1 is generated, so that the input meter 10 fluctuates, giving an illusion to the operator as if the desired signal D wave exists.

[0005]

When a U-wave is present in an adjacent channel and a D-wave is not present, an unnecessary wave (hereinafter referred to as a U-wave) that cannot be completely removed by the BPF is detected and the input level meter fluctuates. In such a case, it is necessary to prevent the meter from swinging.

[0006]

In order to achieve the above object, the present invention provides a band-limited filter (hereinafter referred to as NF) 12 for passing only a U-wave, a U-wave detector 13, and a detector for the U-wave. A variable resistor 14 for setting the voltage to an appropriate value V2;
A differential amplifier 7 for amplifying the difference voltage between V2 and V1.
And a transistor 8 controlled by the output voltage and a diode 11 for synthesizing an AGC voltage which is a differentially amplified output of the detection voltage of the D-wave, thereby eliminating an error in indicating an input meter due to adjacent interference. Is what you do.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. In the figure, the same reference numerals as in FIG. 2 denote the same items. Reference numeral 1 denotes an input terminal for inputting a high-frequency signal having an undefined level, 2 denotes a gain controller for controlling an appropriate level, and 3 denotes an output terminal for outputting a high-frequency signal having a constant level. 4 is a BPF for extracting a required signal D wave from a signal branched from the main signal, 5 is a diode for detecting the signal, 6 is a differential amplifier for amplifying this detection voltage, and 9 is a branch from the control voltage obtained here. And a differential amplifier 10 for amplifying the input voltage.

The BPS 4 and a detecting diode 5 for the output of the BPS 4 and a differential amplifier 6 constitute control means for controlling the output of the gain controller 2 to be kept constant. Differential amplifier 9
And the meter 10 constitute display means for displaying the level according to the output of the control means.

A display control means is constituted by the output of the differential amplifier 7, the transistor 8 and the diode 11.

This circuit partially utilizes an AGC circuit for making the fluctuation of the input level constant at the output. When a high-frequency signal is input from the input terminal 1, the BP
The D wave is selected by F4, and the DC voltage V1 corresponding to the input level is obtained by the detector 5. V1 is amplified by the differential amplifier 6, and the output level is kept constant by controlling the bias of the gain controller 2, and is output from the output terminal 3. That is, as the input signal level increases, V1 also increases and the output of the differential amplifier 6 decreases. However, when a pin diode attenuator is used for the gain controller 2, for example, the attenuation increases and the output level decreases. As a result, the output level of the output terminal 3 is kept constant.

The input level display indicates the level of the input signal using the control voltage. For example, when the input signal level increases, V1 increases and the differential amplifiers 6 and 9 are displayed.
And causes the meter 10 to swing toward the higher level.

When only the U-wave is input from the input terminal 1, the U-wave is selected by the NF 12, detected by the detector 13, and then set to an appropriate voltage V2 by the level adjusting potentiometer 14 to set the differential amplifier. 7 is input to the inverted input side. The detection voltage V1 for the leak of the U wave is input to the non-inverting input side of the differential amplifier 7. Here, V2 is V1
If it becomes larger than a certain fixed value, the transistor 8 is turned on.
If the output voltage of the differential amplifier 7 is lower than the output voltage of the differential amplifier 6, the diode 11 is turned on. Then, the bias voltage VB becomes approximately 0 V, the output level is suppressed, and the meter 10 indicates approximately 0.

Next, when the D wave is input or the U wave disappears, V1 increases or V2 decreases, so that the transistor 8 operates in the cutoff direction, and the bias voltage VB follows V1. Become. In such a case, the AGC voltage and the meter indication corresponding to the input level of the D wave can be naturally obtained.

[0014]

As described above, according to the present invention, even when an interference wave (U wave) exists in an adjacent channel,
In addition to accurately displaying the input level of the signal (D wave) of the own channel, the error of the AGC voltage is reduced and the output level can be maintained at a constant rated value.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing an embodiment of the present invention.

FIG. 2 is an overall block diagram showing a conventional embodiment.

[Explanation of symbols]

4: D-wave BPF, 5: D-wave detector, 6: D-wave differential amplifier, 12: U-wave NF, 13: U-wave detector, 7:
Differential amplifier for detecting level difference between D wave and U wave

Claims (2)

[Claims] A band-pass filter for passing a required wave, a band-limited filter for passing only an unnecessary wave, an AGC circuit for detecting the required wave and controlling a gain, and a detector for an unnecessary wave;
A variable resistor for setting the detection voltage of the unnecessary wave to a predetermined value, a differential amplifier for amplifying a difference voltage between the output voltage of the variable resistor and the detection voltage of the required wave, and control by the differential output voltage An input level indicating circuit having an adjacent interference removing function, comprising: a transistor to be operated; and a diode for synthesizing an AGC voltage which is a differential amplification output of the detection voltage of the required wave. 2. A gain controller, a band-limited filter connected to an input side of the gain controller for passing and outputting an unnecessary wave component of an input signal, a detector for outputting the band-limited filter, and the gain control. A bandpass filter connected to the output side of the filter for passing and outputting a required wave of an output signal; a detector for outputting the bandpass filter; and maintaining the output of the gain controller constant according to the output of the detector. Control means for controlling, display means for displaying the level in accordance with the output of the control means, output of the detection means for the output of the band-pass filter, and output of the detection means for the output of the band-limited filter as inputs. An input level instruction circuit, comprising: a differential amplifier; and a display control unit that controls the display unit to lower the level of the control unit according to an output of the differential amplifier.