JPH0678177A - Frequency characteristic correcting system - Google Patents

Abstract

PURPOSE:To easily set up a frequency correcting coefficient by a simple circuit constitution by adding a frequency characteristic correcting reference signal to a horizontal or vertical blanking period and detecting the reference signal. CONSTITUTION:A reference signal generating circuit 3 generates a reference frequency signal in a frequency band to be corrected such as sub-carrier frequency to be added to a prescribed position of a horizontal blanking period. The reference frequency signal outputted from the circuit 3 is added to an input video signal by an adder 2 and the added signal is impedance-reduced through an impedance converter 4. An output from the converter 4 is inputted to a smoothing amplifier 8 and a wide band amplifier 9 through a coaxial cable 5. A multiplier 9 is controlled in its multiplication rate in accordance with the level of the reference frequency signal set up in a setter 17 and multiplies respective video signals outputted from both amplifiers 8, 9. Consequently a frequency correcting coefficient can easily be set up by the simple circuit constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic frequency characteristic correction circuit for compensating for frequency characteristic deterioration of a video signal transmitted by a coaxial cable.

[0002]

2. Description of the Related Art As a conventional technique, there is a method of switching the correction amount of the frequency characteristic in a fixed step (for example, the length of the coaxial cable is every several hundreds of meters). In this correction, it is necessary to manually switch the correction amount, and it is impossible to perform the correction during the step. A variable equalizer method is known as an automatic frequency characteristic correction method, but if the characteristics of the positive feedback amount and the negative feedback amount are not perfectly matched, the frequency characteristic is distorted and appears as waveform distortion. In addition, the attenuation characteristic of the frequency characteristic of the coaxial cable is not the local off characteristic but also the change of the low frequency characteristic, and the setting of the correction coefficient requires a correction circuit having a correction coefficient of several orders. It cannot be obtained in the positive feedback system and the negative feedback system, and the waveform distortion is increasing.

[0003]

The above-mentioned prior art has the above-mentioned drawbacks. SUMMARY OF THE INVENTION It is an object of the present invention to eliminate these drawbacks and to realize a frequency characteristic correction circuit which has a simple circuit configuration and can easily set a frequency correction coefficient.

[0004]

In order to achieve the above object, the present invention adds a reference signal for frequency characteristic correction to a horizontal or vertical blanking period in an automatic frequency characteristic correction method. With a configuration that detects and automatically corrects the reference signal, the frequency characteristics of the coaxial cable for video signal transmission, especially the high-frequency characteristics are degraded, and the frequency characteristics of various video processing circuits are degraded when multiplex transmission processing is performed. And the change, the signal of the flat frequency characteristic and the signal of which the high range of the frequency characteristic is raised are input to the multiplication circuit, and the multiplication coefficient is increased in the high range from the flat characteristic of the output frequency characteristic by the control signal. The frequency characteristic is corrected by using a circuit whose characteristic is variable. Further, the coefficient for frequency characteristic correction can be performed by adjusting only the signal in which the high frequency range of the frequency characteristic is increased according to the deterioration characteristic.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 denotes a video signal input terminal, and the video signal input here is input to the addition circuit 2. A reference signal generating circuit for generating a reference frequency signal in a frequency band to be corrected such as a subcarrier frequency added at a predetermined position in the horizontal blanking period is connected to the other input terminal of the adding circuit 2. The addition circuit 2 adds the video signal and the reference frequency signal, the impedance conversion circuit 4 lowers the impedance, passes through the coaxial cable 5, and inputs the hum canceller circuit 6. The hum canceller circuit 6 removes the disturbance signal superimposed during the transmission of the coaxial cable 5, the gain control circuit 7 controls the gain to a specified gain, and then passes through a flat amplifier 8 having a flat frequency characteristic to a multiplication circuit 9. input.

The output of the gain control circuit 7 passes through the high frequency amplifier 10 for increasing the high frequency and is input to the other input terminal of the multiplication circuit 9, and the multiplication circuit 9 receives the control signal from the control terminal. From the flat frequency characteristic, the output of the characteristic in which the high frequency is increased is output, the DC potential is stabilized by the clamp circuit 11, the impedance is reduced by the impedance conversion circuit 12, and the image is output to the output terminal 13. Output as signal output. The output of the clamp circuit 11 detects the peak level of the reference frequency signal added to the horizontal blanking period of the video signal by the peak detection circuit 14, and converts the peak level potential detected by the sample hold circuit 15 into a DC voltage. To do. The output of the sample-hold circuit 15 is input to the comparison amplifier 16, and a setter 17 that generates a set voltage set to the level of the reference frequency signal is connected to the other input terminal of the comparison amplifier 16. The comparison amplifier 16 outputs the frequency characteristic correction signal to the control terminal of the multiplication circuit 9 so that the output voltage of the sample hold circuit 15 and the output voltage of the sample hold circuit 15 become the same voltage to stabilize the frequency characteristic.

From the above, even if the cable length of the coaxial cable 5 changes and the frequency characteristic changes, the frequency characteristic can be automatically corrected. Further, the frequency characteristic to be corrected can be corrected by changing the correction coefficient and the order of only the high frequency amplifier 10 that raises the high frequency, and this change can be performed by changing the values of the resistor, the capacitor, etc. The frequency characteristics can be easily set. Here, as the reference frequency signal added to the horizontal blanking period, the same operation can be performed by using a method using a burst signal or adding it to the vertical blanking period. Further, the gain control circuit 7 can also perform automatic gain control by using the gain control reference pulse as in the frequency characteristic correction. Further, if the flat amplifier 8 having a flat frequency characteristic is used to reduce the high frequency of the frequency characteristic, it is possible to correct from the characteristic of increasing the high frequency to the characteristic of decreasing the high frequency. The same applies to the case where a multi-core cable is used as the coaxial cable 5, and even if this system is increased, this system can be similarly increased and performed. The same can be applied to the video system in which the ham canceller circuit 6 is replaced with the multiplex transmission processing circuit from the coaxial cable 5. When the coaxial cable 5 is long and cannot be corrected by the frequency characteristic correction circuit described above, the number of frequency characteristic correction circuits can be increased. Further, it is possible to use the conventional step type frequency characteristic correction circuit in common and perform the correction during the step. The reference frequency signal added during the horizontal or vertical blanking period can be removed by using a blanker circuit or the like.

[0008]

According to the present invention, it is possible to realize an automatic frequency characteristic correction circuit which can easily set the frequency correction coefficient with a simple circuit configuration.

[Brief description of drawings]

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

[Explanation of symbols]

 3 Reference Signal Generation Circuit 5 Coaxial Cable 8 Flatness Amplifier Circuit 9 Multiplier Circuit 10 High Band Amplifier 14 Peak Detection Circuit 15 Sample Hold Circuit 16 Comparison Amplifier

Claims (1)

[Claims] 1. In a system in which a reference frequency signal having a frequency serving as a reference of a frequency band to be corrected is added to a video blanking period of a video signal and the signal is transmitted through a transmission line such as a coaxial cable, the transmitted frequency characteristic is flat. Video signal,
A frequency characteristic correction method, characterized in that a multiplication ratio of a video signal having an increased high frequency characteristic is controlled according to a level of a reference frequency signal added to the transmitted video blanking period.