JPS61148986A - Television signal sampling device - Google Patents

Abstract

PURPOSE:To extend the application of the TV synchronization by sampling with the frequency of multiplication of the TV frame frequency by a rational number, to transmit the TV signal at a transmission rate within the spe cifications by a TV synchronization of excellent picture quality. CONSTITUTION:A PLL2 generates the sampling frequency from the TV signal of the image picked up by a camera 1. In this case, in the circuit 2, the frame frequency is detected from the TV signal by a frame frequency detecting circuit 21, and a correspondent clock is generated. Meanwhile, the output of a VCO22 that generates the sampling frequency is divided by a dividing circuit 22, and a clock is generated. The phase difference between this clock and the output from the circuit 21 is checked by a comparator 24. Then the clock is smoothed by a smoothing circuit 25, and the result is supplied to the control terminal of a VCO22. In result, the VCO22 generates a sampling frequency of the product of the frame frequency and the value decided by the circuit 23, therefore, the frame frequency is given a clock.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a sampling method for television signals (hereinafter referred to as TV signals), and in particular, even when the transmission speed is specified by the standards on the transmission line side. This invention relates to setting a sampling frequency that can provide high quality images with a simple device.

[Background of the invention]

The following three methods are known as conventional methods for setting the sampling frequency of TV signals.

(1) TV synchronization: Detect the horizontal frequency and burst frequency of the TV signal, and multiply this by a rational number to obtain the sampling frequency.

Since the sampling frequency is locked to the TV signal, high image quality is generally obtained. However, since it generally does not meet the transmission line standards, its use is restricted.

(Two-line interval: The sampling frequency is the transmission rate determined by the transmission line standard divided by a predetermined value. Since the sampling frequency is not locked to the TV signal, the sampling frequency is There were problems such as fluctuations in the frame, vibrations in the contour, and the inability to use interframe coding that predicts the difference between frames.

(3) Independent synchronization 2 In order to solve the problems of the above two methods, the TV signal is sampled at a frequency locked to the TV signal,
During transmission, unnecessary signals are added to match the transmission speed of the above standard. However, this method requires large-scale equipment to match the sampling frequency and transmission rate, and jitter occurs when the receiving side equipment reproduces the original sampling frequency from the transmission rate, resulting in poor image quality. [Object of the Invention] The purpose of the present invention is to solve the problems of the above three methods by using the most desirable TV synchronization from the viewpoint of both image quality and device scale. The goal is to set a sampling frequency that meets the standards.

[Summary of the invention]

In order to meet the above object, the present invention provides that the transmission speed standard of the transmission line has a certain tolerance range with respect to the center speed,
Focusing on the fact that this allowable range is wider than the frame frequency of the TV signal, samples are taken so that the frequencies within the above allowable range are divided by a predetermined value, and the frequency is a rational number multiple of the frame frequency. This feature is characterized by setting the oscillation frequency.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. This figure is a block diagram of a high-efficiency encoding device for TV signals. The present invention is defined by P L L (Ph
(ased Locked LOOp), and the others are the same as before. In order to facilitate the subsequent explanation, we will first explain the same parts as before.

From the TV signal captured by the camera 1, the PLL 2' generates a sampling frequency using a method described later. In accordance with this sampling frequency, the A/D converter 3 performs analog/digital conversion on the TV signal, and the encoder 4 highly efficiently compresses the result and sends it to the transmission line 5.

Conversely, on the receiving side, the PLL 6 extracts a cyclic clock from the received data, and multiplies this clock by a predetermined rational number to obtain the sampling frequency. According to this sampling frequency, the decoder 7 restores the original TV signal and D
/A converter 8 performs digital/analog conversion, and the result is displayed on monitor 9.

Next, the present invention will be explained with reference to FIG. This figure is a block diagram of PLL2. The operation is equivalent to a normal PLL.

That is, by the frame frequency detection circuit 21, jo, T
A frame frequency is detected from the V signal, and a clock corresponding to this is generated. On the other hand, a frequency dividing circuit 23 divides the output of a voltage controlled oscillator (VCO) 22 that generates a sampling frequency to generate a clock. A comparator 24 detects the phase difference between this clock and the output of the frame frequency detection circuit 21.
, smoothed by the smoothing circuit 25, and the result is given to the control terminal of the voltage control oscillator 220 mentioned above. As a result of the above,
The sampling frequency generated by the voltage controlled oscillator 22 is the result of multiplying the frame frequency by a value determined by the frequency dividing circuit 23, and is locked to the frame frequency.

Various methods of implementing the frame frequency detection circuit 21 are also known. An example of this is to detect the horizontal synchronizing signal of the TV signal, find the horizontal scanning frequency of the TV signal, and divide the result by the number of scanning lines of the TV signal. This is also well known, so a detailed explanation will be omitted.

Next, numerical examples will be shown when the present invention is actually implemented. As is well known, the transmission speed standard for the third group of transmission lines in Japan is 3L.
064 megapits per second ±10 ppm. Assuming that the TV signal is encoded with 4 bits per sample point, the sampling frequency should be 8.016 MHz±10 ppm.

Furthermore, the frame frequency of the NT8C signal, which is the Japanese standard for TV signals, is 29.97 Hz. Dividing the sampling frequency by the frame frequency is 267467.467±10ppm
becomes. That is, the sampling frequency is 267 times the frame frequency.
From 464.792 times to 267470.172 times? Can be set within a range. .

For example, it may be set to 267,465 times, 267,469.5 times, etc. In the former case, the phase difference between the two clocks can be compared every frame period of the TV signal, so the period is 1/30Hz=33rr@. In the latter case, the decimal point is 0.5, so L66 is required every two frames.
It becomes large as m seconds. Therefore, in principle, the jitter between the two clocks is smaller for the former and larger for the latter, and this value is 26746
If it is set to 6.5, this period will be further shortened. That is, there are 525 horizontal scanning lines in one frame of a TV signal, but the above value and the number of horizontal scanning lines in a frame can be divided by a common divisor of 10.5, resulting in 25,473 and 50, respectively. Therefore,
Comparisons can be made every 50 horizontal scan lines. Since the horizontal scanning frequency is 525 times the frame frequency of 29.97 Hz, the time is shortened to 50/(29,97×525)=3.2 msec.

In the above embodiment, the case where a TV signal is highly efficiently encoded has been explained as an example, but the present invention can also be applied to the case where the result of analog/digital conversion is transmitted without high efficiency encoding. it is obvious.

Further, as for transmission, in addition to general communication, there is also the case of writing to a recording device.

〔Effect of the invention〕

As explained above, according to the present invention, a TV with good image quality
Since TV signals can be transmitted through synchronization at a transmission speed within the standard range, the fields of application to which this TV synchronization can be applied are expanded, and the practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a high-efficiency encoding device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a PLL section for explaining this embodiment in FIG.

Claims (1)

[Claims] A television signal characterized in that it is sampled at a frequency that is close to the standard value of the transmission speed of the transmission path or the result of dividing this standard value by a predetermined value, and is a rational number multiple of the frame frequency of the television signal. Sampling device.