JPS59131284A - Picture recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent chrominance noise due to noise bar from being generated by holding a result of detection of a chrominance signal before a section where an amplitude of burst region attains a prescribed amplitude or below in one frame period. CONSTITUTION:A burst region signal (a) of a chrominance signal is compared with an output of a reference oscilator 3 by a phase comparator 1 so as to detect the presence of the chrominance signal and it is inputted to an amplitude detector 6, and an output voltage of the amplitude detector 6 is set so as to be decreased when the amplitude becomes >nearly 1/2 of normal value and the result is led to a holding circuit 7. The holding circuit 7 holds an output of the comparator 1 when the output of the amplitude detector 6 is decreased and outputs it to a voltage comparator 4 compring the output with a reference power supply. Even if many noise bars are generated in one field, since the chrominance signal detecting output is held, no chrominance noise is generated.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an image recording and reproducing device.

Conventional configuration and its problems C
The function of detecting the presence or absence of a single color signal (generally called a color killer) has become an essential function for the following reasons.

It is well known that in devices such as image recording and reproducing apparatuses, phase fluctuations (jitter) occur during recording and reproducing, and that a normal demodulation system has a function (APC, AFC, etc.) to correct this. This is because the C color signal in the recording and reproducing apparatus also has a similar function. This function works effectively when there is a color signal and corrects phase fluctuations, but when there is no color signal it outputs a large amount of noise.

Therefore, a function is required to detect the absence of the °C1 color signal and prevent output of noise in °C, and this function is a color killer.

Conventionally, in order to detect the presence or absence of this color signal, the frequency of the burst region of the color signal and the reference frequency (for example, 8.579
545 MHz) to determine the temperature.

This is a convenient function that can be used immediately when a frequency shift corresponding to a frequency shift amount within a range in which phase fluctuation can be corrected occurs, and highly accurate discrimination can be made. FIG. 1 shows a simple block diagram of this function. The burst region signal (a) of the color signal and the output of the reference oscillator (3) are input to the phase comparator (1) and compared. As a result, if the respective frequencies are close, a low voltage is output, and if there is a difference of "C", a low voltage is output and input to the voltage comparator (4).

Voltage comparison! Since the reference voltage of the reference power supply (5) is input to the other input terminal of (4), this voltage is compared with the output of the phase comparator (1) to generate a switching signal, that is, a color killer signal. Output. By setting the reference voltage to a voltage corresponding to a frequency shift whose phase can be corrected, accurate detection of the presence or absence of a color signal becomes possible.

By the way, it is ideal for an image recording and reproducing device to be able to perform stable recording and reproducing at all times, but it is difficult to obtain stable characteristics at °C due to y1 touch, dropout, special reproduction, etc. Particularly in special playback, between the recorded pattern and the playback head trace, playback of one or more unrecorded sections is inevitably introduced within one field period due to track misalignment. be done. This section is usually 1
It is called a noise bar and is well known. Since the color signal naturally disappears in the noise bar section, it is detected that there is no color signal, and the output of the color signal is turned off to suppress noise. However, in special playback where a large number of noise bars occur in one field, the color signal may not be output many times (as a result, the receiver may malfunction, causing problems such as the C color becoming untidy or disappearing). In order to prevent this malfunction, a method has been proposed to integrate the output of the phase comparator (1), but it is impossible to always maintain a potential above the reference voltage, and the reference voltage You have to set it low. This is because the reference voltage is low, so accurate operation cannot be expected, so if you play back something that contains a lot of noise and has no color signal, it will malfunction and produce color noise. There were drawbacks.

OBJECT OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional technology.
An object of the present invention is to provide an image recording and reproducing device that can prevent malfunctions of a receiver without reducing the accuracy of 93-bit output.

Structure of the Invention In order to achieve the above object, the image recording and reproducing apparatus of the present invention comprises:
The detecting means detects the presence or absence of the "C" color signal by comparing the frequency of the burst region of the reproduced color signal with a reference frequency, and the detecting means detects the presence or absence of the "C" color signal by comparing the frequency of the burst region of the reproduced color signal with a reference frequency. The configuration is such that detection results before this interval are held in an interval in which the amplitude is less than or equal to a predetermined amplitude.

DESCRIPTION OF EMBODIMENTS Hereinafter, one embodiment of the present invention will be explained based on the drawings.
explain. , FIG. 2 is a block diagram of a circuit for detecting the presence or absence of a color signal, and the same components as in FIG. 1 are given the same reference numerals. The burst region signal (a) of the color signal is input to the phase comparator (1) and also to the amplitude detector (6), and when the amplitude becomes about 1/2 or less of the normal value, the output voltage decreases. 'C' is set so as to be introduced into the holding circuit (7). The holding circuit (7) includes a phase comparator (
1) is input, and when the voltage from the amplitude detector (6) drops, a sample hold operation is performed to hold the output of the comparator (1), and the output is output to the voltage comparator (4).

By the above-mentioned operation, a stable color signal detection signal can be obtained by the operation of the holding circuit (7) even during special reproduction in which many drops in burst amplitude occur within one field period.

FIG. 3 is a circuit diagram of the amplitude detector (6) and holding circuit (7). The burst region signal (a) of the color signal is converted into a 4W wave by a diode (Dl) and a capacitor (C1), and converted into a DC voltage proportional to the amplitude. This r
[The amplitude of the burst region is reduced to 1/2 of the normal amplitude because the current voltage is used to operate the C transistor (Ql).]
The value of the bias resistor (R+) (R2) is set so that when the voltage drops to about V, the base potential of the transistor (Q,) becomes below the collector-emitter open potential.

By the way, when the burst region swings normally, the collector-emitter field of the transistor (Ql) is in a conductive state, so the VBE of the transistor (Q2) is approximately 0 [v
], and VCE is an electric voltage of 10 VCC. Furthermore, when the amplitude of the burst region becomes about 1/2 or less of the normal amplitude, the VCE of the transistor (Qρ becomes almost the ground voltage. Therefore, the collector voltage of the transistor (Q2) can be used as the amplitude detection signal of the burst region. This amplitude detection signal is introduced to the gate of the analog switch (SWl).The analog switch (SWl) is a functional element that conducts between the terminals if the signal introduced to the gate is at the power supply potential, and opens if the signal is at the ground potential. By connecting the output end of the phase comparator (]) to the terminal (a) and the input end of the voltage comparator (4) to the terminal (b), the analog switch (SWl) and the resistor can be connected. (R3), capacitor (C
A sample and hold circuit according to 2) is constructed. In addition(
R4) (R5) is a resistance. According to this configuration, the potential of the terminal (a) immediately before the collector potential of the transistor (Q2) becomes the ground potential is held at the terminal (b) until the collector potential of the transistor (Q2) becomes the power supply potential next time. . However, when the amplitude of the C1 burst region becomes less than 1/2 degree, which is necessary for special reproduction, etc., the collector potential of the transistor (Q2) becomes the ground potential, and the phase comparator (1) just before it becomes the ground potential. The output potential of voltage comparator (4)
will be retained for input.

As described in detail, according to the present invention, the presence or absence of a color code can be stably detected without adding an integral.

Since no integral is added, the accuracy can be sufficiently increased, and malfunctions of the receiver can be reliably prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a circuit for detecting equalization of a color signal in a conventional image recording and reproducing device, and Fig. 2 is a circuit for detecting heat dissipation of a color signal in an image recording and reproducing device according to the present invention. FIG. 3 is a circuit diagram of the interpupillary distance detector and holding circuit. (1)...Phase comparison path, (3)...Reference oscillator, (
4) Voltage comparator, (5) Base ring-power supply, (6
)...Amplitude detection 8h, (7)...Holding circuit. Agent Yoshihiro Morimoto Figure 1 Figure 3

Claims (1)

[Claims] 1. A detection means for detecting the presence or absence of a color signal by comparing the frequency of the burst region of the reproduced color signal with a reference frequency; An image recording and reproducing device configured to hold detection results before a section in which the amplitude is less than or equal to a predetermined amplitude.