JP2654156B2 - Fading monitoring circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a fading monitoring circuit that monitors a drop frequency and a drop depth of selective fading that occur in a propagation path or the like in the field of wireless communication.

[Prior art]

FIG. 2 shows, for example, IEICE Transactions '82 /1Vol.J65-
B, is a block diagram of a conventional fading monitoring circuit particularly for flat fading, which is shown in connection with the paper "Automatic equalizer for selective fading" described in No. 1, where 1 is a variable. An attenuator, 2 is a first amplifier, 3 is a second amplifier, 4 is a power detector, 5 is a feedback amplifier, 6 is an input terminal, 7 is an output terminal, and 8 is a feedback voltage monitoring output terminal. Thus, this conventional circuit constitutes an AGC amplifier that automatically amplifies a received power that changes every moment due to fading generated in a propagation path to a constant level. Next, the operation will be described. The signal with the level fluctuation input from the input terminal 6 is attenuated by the variable attenuator 1 and then amplified by the first and second amplifiers 2 and 3. , And then DC amplified by the feedback amplifier 5 and sent to the variable attenuator 1 as a control voltage to drive the variable attenuator 1. That is, when the signal input from the input terminal 6 is attenuated, the first and second amplifiers 2, 3
Detection level in the power detector 4 after the amplification by
Therefore, when the control voltage decreases, the amount of attenuation of the variable attenuator 1 decreases, and the signal power output to the output terminal 7 becomes a negative feedback circuit. In this case, in the conventional circuit of FIG. 2, the voltage output from the feedback amplifier 5 for monitoring the control voltage changes in proportion to the signal power input to the input terminal 6, and therefore fluctuates due to fading. This shows that the level fluctuation is used as a fading monitoring circuit of flat fading that can be monitored as a voltage value.

[Problems to be solved by the invention]

Since the conventional fading monitoring circuit is configured as described above, it is a flat fading monitoring circuit that monitors the level fluctuation due to the fading of the input signal as a voltage value, so that waveform distortion in the transmission band is a problem. There is a problem that monitoring of selective fading cannot be performed. That is, the conventional circuit monitors the entire power in the transmission band, and is not suitable for a circuit that monitors the selective waveform distortion generated in the transmission band. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a fading monitoring circuit suitable for monitoring waveform distortion in a transmission band due to selective fading.

[Means for Solving the Problems]

The fading monitoring circuit according to the present invention automatically equalizes waveform distortion in a frequency domain by a variable resonance circuit,
A variable low-pass filter is disposed before or after the variable resonance circuit to correct asymmetry with respect to the center frequency of the variable resonance circuit. When the voltage value of the resistor is equal to or less than a predetermined voltage value by the monitoring voltage processing circuit, the frequency output is output. The voltage output to the terminal is set to 0, and when the voltage value of the resistor is equal to or higher than a predetermined voltage value, a voltage related to the drop frequency is output to the frequency output terminal. Is to be monitored.

[Operation]

The fading monitoring circuit according to the present invention monitors the depth of the selective fading drop by using a resistor provided between the variable resonance circuit and the variable low-pass filter. When the voltage value of the resistor is equal to or less than a predetermined voltage value, the frequency is monitored. By setting the voltage output to the output terminal to 0 and outputting the voltage related to the drop frequency to the frequency output terminal when the voltage value of the resistor is equal to or higher than the predetermined voltage value, the drop frequency and the drop depth of the selective fading can be obtained. And monitor.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 9 denotes a variable resonance circuit as an automatic equalizer for equalizing waveform distortion in a frequency domain, 10 denotes a resonance circuit constituting the variable resonance circuit 9, and 16 denotes a resonance frequency of the resonance circuit 10 automatically. A variable capacitance element to be controlled, 17 is a bias resistance of the variable capacitance element 16, 18 is a resistor, 19 is an input terminal of a control signal from a control unit (not shown) applied to the variable capacitance element 16, 20 is a monitoring voltage processing circuit, 21 Is a voltage output terminal related to the fading frequency, 22 is a voltage output terminal related to the fading depth, 23 is a carrier input terminal, 24
Is a carrier output terminal, 25 is a variable low-pass filter, 26 is a variable resistance element for correcting asymmetry with respect to the center frequency of the variable resonance circuit 9, 27 is a capacitor as a high-frequency short-circuit capacitor, and 28 is a variable resistance element 26. Bias resistors, 29, 30
Is a resistor for monitoring the current flowing through the variable resistance element 26, and 31 is an input terminal for a control signal applied to the variable resistance element 26 from a control unit (not shown). Next, the operation will be described. The carrier with the channel distortion due to the selective fading exhibits a spectrum on which the characteristics of the anti-resonance circuit are superimposed, and the carrier having the waveform distortion in such a frequency domain is converted by the variable resonance circuit 9 as an automatic equalizer. Automatic equalization of the waveform distortion is possible. That is, by automatically controlling the center frequency and the sharpness of the series resonance characteristic provided in the variable resonance circuit 9,
It is possible to perform equalization that follows the anti-resonance characteristics of a carrier subjected to selective fading distortion. In the embodiment shown in FIG. 1, only the variable resonance circuit 9 as an automatic equalizer is shown, and the detection unit and the control unit are not shown. The control signal fed back from the controller is input, and the sharpness Q of the resonance circuit 100 is variably controlled by the control signal, and the variable low-pass filter 25 is used to compensate for asymmetry about the center frequency of the resonance characteristic. The characteristics are also variably controlled.
The control current flowing through the variable resistance element 26 is related to the depth of the selective fading, so that the current flowing through the resistor 28 indicates the depth of the selective fading, and the potential difference between both ends of the resistor 28 is As compared to the current, the voltage that can be monitored by the resistors 29, 30 is indicative of the depth of the selective fading. On the other hand, a control signal fed back from the control unit is input to the input terminal 19 to variably control the center frequency of the resonance circuit 10,
Follow the drop frequency of selective fading. Thus, the voltage value of the control signal corresponds to the center frequency of the variable resonance circuit 9, that is, represents the drop frequency of the following selective fading. Also resistance 18
Is for monitoring the voltage applied to the variable capacitance element by the monitoring voltage processing circuit 20. Further, the monitoring voltage processing circuit 20 monitors the depth of the selective fading drop by the resistors 29 and 30, and further monitors the drop frequency by the resistor 18. As a result, a voltage indicating the drop frequency is output to the voltage output terminal 21 and the voltage output terminal 22
Outputs a voltage representing the depth of the drop. In this case, since a voltage that determines the center frequency of the variable resonance circuit 9 is applied to the resistor 18 even when the selective fading does not occur, when the voltage value of the resistors 29 and 30 becomes lower than a certain voltage, The voltage output to the voltage output terminal 21 becomes 0, indicating that no selective fading has occurred. When the voltage values of the resistors 29 and 30 are equal to or higher than a certain voltage, a voltage representing the drop frequency is output from the voltage output terminal 21. In the above embodiment, the monitoring voltage processing circuit 20 is provided,
A threshold value is provided for the voltage values of the resistors 29 and 30. When the voltage value is lower than a certain voltage value, the voltage output to the voltage output terminal 21 is set to 0. May be omitted. Further, in the above embodiment, the variable low-pass filter 25 is provided after the variable resonance circuit 9, but may be provided before.

【The invention's effect】

As described above, according to the present invention, the waveform distortion is automatically equalized in the frequency domain by the variable resonance circuit,
A variable low-pass filter is disposed before or after the variable resonance circuit to correct asymmetry with respect to the center frequency of the variable resonance circuit. When the voltage value of the resistor is equal to or less than a predetermined voltage value by the monitoring voltage processing circuit, the frequency output is output. The voltage output to the terminal is set to 0, and when the voltage value of the resistor is equal to or more than a predetermined voltage value, a voltage related to the drop frequency is output to the frequency output terminal. And a fading monitoring circuit capable of monitoring selective fading without using an expensive fading analyzer is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a fading monitoring circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional fading monitoring circuit. 9 is a variable resonance circuit, 10 is a resonance circuit, 16 is a variable capacitance element,
25 is a variable low-pass filter, 26 is a variable resistance element, and 27 is a capacitor (capacitance element).

Claims (1)

(57) [Claims] A variable resonance circuit as an automatic equalizer for equalizing waveform distortion in a frequency domain, comprising a resonance circuit and a variable capacitance element for automatically controlling a resonance frequency of the resonance circuit. A variable low-pass filter comprising a variable resistor element and a high-frequency short-circuiting capacitive element arranged at the front or rear stage to correct asymmetry with respect to the center frequency of the variable resonance circuit; and the variable resonance circuit and the variable low-pass filter. A resistor for monitoring the depth of the selective fading is provided in between, and a frequency output terminal for outputting a voltage related to the dip frequency and a depth output terminal for outputting a voltage related to the dip depth are provided. Provided,
When the voltage value of the resistor is equal to or lower than a predetermined voltage value, the voltage output to the frequency output terminal is set to 0, and when the voltage value of the resistor is equal to or higher than the predetermined voltage value, a voltage related to the drop frequency is applied to the frequency output terminal. And a monitoring voltage processing circuit that outputs a signal.