JPS642298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplitude equalization circuit that equalizes amplitude distortion due to selective fading occurring in a wireless transmission path.

FIG. 1 shows the configuration of an amplitude equalization circuit using a conventional variable resonant circuit. As shown in this figure, the conventional amplitude equalization circuit uses bandpass filters 4 to 6 and detectors 7 to 9 to adjust the spectrum levels at both ends and the center of the signal band at the output 2 of the variable resonant circuit 3.
The control circuit 10 controls the center frequency and sharpness of the variable resonant circuit 3 so that these three levels are equal.

Although this circuit effectively operates against amplitude distortion due to typical two-wave interference, it cannot sufficiently equalize distortion when amplitude distortion has a first-order slope such as three-wave interference. This situation is shown in FIG. A waveform 101 represents the amplitude frequency characteristic due to fading, and a waveform 102 represents the amplitude characteristic of the variable resonant circuit.

At this time, the amplitude characteristic of the variable resonant circuit output is waveform 1
It will look like 03. In other words, both ends of the signal band 1
At frequencies 04, 105 and center 106, although the levels at the three points are controlled to be equal, the amplitude frequency characteristics within the signal band are not flat but S-shaped.

This is because the center frequency of the facing and the center frequency of the resonant circuit do not match.

An object of the present invention is to provide an amplitude equalization circuit that can also equalize amplitude distortion having a first-order slope such as three-wave interference.

In order to achieve the above object, the amplitude equalization circuit according to the present invention has three narrowband filters that pass the frequencies at both ends and the center of the transmission band. A primary slope correction circuit capable of changing the amplitude characteristics of the primary slope is installed upstream of the variable resonant circuit whose sharpness is controlled, and a second slope correction circuit whose output has the same resonant frequency as that of the variable resonant circuit is connected to the output of the variable resonant circuit.
A resonant circuit is provided, and a level detector detects the output level of the second resonant circuit, and the S of the variable resonant circuit is determined by the output of the level detector.
A second control circuit is provided to control the primary slope correction circuit so as to obtain a letter-shaped amplitude characteristic and eliminate this amplitude characteristic.

With such a configuration, amplitude characteristics other than two-wave interference can be sufficiently equalized, and the object of the present invention can be completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 3 shows an embodiment of an amplitude equalization circuit according to the present invention. 1 is an input terminal, 2 is an output terminal, 3 is a variable resonant circuit, 4 to 6 are band pass filters, 7 to 9 are detectors, and 10 is a control circuit, and these parts are the same as the conventional circuit configuration.

Reference numeral 11 denotes a second resonant circuit that is the same as the variable resonant circuit 3, and the center frequencies of both are made equal by the control signal 15. 12 is a level detector that detects the level of the signal that has passed through the second resonant circuit 11; 13 is a second control circuit that outputs a control signal 18 based on the output information of the level detector; 14 is a CR L-type circuit; This is a primary slope correction circuit whose CR is controlled by the control signal 18 of the second control circuit 13.

As mentioned above, the control signal 15 of the control circuit 10
and 16, the center frequency and sharpness of the variable resonant circuit 3 are controlled, and the levels of the bandpass filters 7 to 9 are made equal. However, when a signal distorted by fading, which is not secondary interference, is input to terminal 1, an S-shaped waveform as shown in FIG. 2 is output to terminal 2 of this circuit. Here, the frequency at which the level of this S-shaped amplitude characteristic is maximum is approximately equal to the center frequency of the resonant circuit 3. Therefore, assuming that the amplitude characteristics of the primary slope correction circuit 14 are initially flat, the resonance circuits 3 and 11
Since the center frequencies of the resonant circuit 11 are made equal, the output level of the resonant circuit 11 increases, and the output voltage of the wave detector 12 increases. The control circuit 13 thereby detects that the amplitude characteristic is S-shaped. The primary slope correction circuit 14 is then controlled so that this becomes a constant value, that is, it disappears. The CR is changed in the primary slope correction circuit 14, and the primary slope correction is performed in the resonant circuit 3 to equalize amplitude distortion caused by three-wave interference and the like.

Although the embodiment in which the primary slope correction circuit is constituted by a CR L-type circuit has been described above, the primary slope correction circuit may be constituted by other types of circuits. Further, the second control circuit can be configured by an analog circuit or a digital circuit. In short, the primary slope correction circuit and the second control circuit are
If the level near the center frequency of the resonant circuit increases, the circuit is not limited to this embodiment as long as it can lower the level.

As described above, according to the present invention, even when fading other than two-wave interference occurs, the amplitude residual after equalization does not become S-shaped, making it possible to perform better amplitude equalization.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional amplitude equalization circuit, FIG. 2 is a diagram showing an amplitude residual generated in a conventional amplitude equalization circuit, and FIG. 3 is a circuit diagram showing an embodiment of an amplitude equalization circuit according to the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1...Input terminal, 2...Output terminal, 3...Variable resonance circuit, 4-6...Band filter, 11...Second resonance circuit, 13...Second control circuit, 14...Primary slope correction circuit.

Claims (1)

[Claims] 1 A primary filter is installed before a variable resonant circuit whose center frequency and sharpness are controlled so that the three levels detected by three narrow band filters that pass the frequencies at both ends and the center of the transmission band are equal. A primary slope correction circuit that can change the amplitude characteristic of the slope is provided, and a second resonant circuit having the same resonant frequency as the variable resonant circuit is provided at the output of the variable resonant circuit, and the output level of the second resonant circuit is detected. and a second control circuit for controlling the primary slope correction circuit so that the S-shaped amplitude characteristic of the variable resonant circuit is obtained by the output of the level detector and the amplitude characteristic is eliminated. An amplitude equalization circuit featuring: