KR920005658B1 - Frequency stabilization circuit of reference signal using horizontal synchronous signal of video signal - Google Patents

Abstract

The circuit utilizes horizontal synchrounous signal as reference signal to stabilize frequency of reference signal generated by local oscillators provided in the television. The circuit includes an oscillator (2) for generating pulse signal having the same period as that of horizontal synchronous signal, a frequency divider (3) for generating standard signal, a variable frequency oscillator (4) for generating reference signal, a variable frequency divider (7) for generating standard frequency suited to NTSC, PAL, and SECAM type, a phase comparator (8) for comparing phases of output signal of the frequency divider (3), and the variable frequency divider to generate phase difference signal (PS) and for generating selection signal (CS), and a low pass filter (9) for adjusting oscillation frequency of the variable frequency oscillator (4).

Description

Frequency stabilization circuit of reference signal using horizontal synchronization signal of video signal

1 is a block diagram showing a frequency stabilization circuit of the present invention.

2 (a)-(g) are operating waveform diagrams of the parts of FIG.

* Explanation of symbols for main parts of the drawings

1: sync signal separator 2: horizontal synchronous re-oscillator

3: horizontal synchronous divider 4: variable oscillator

5: reference signal divider 6: selector

7: Variable divider 8: Phase comparator

9: Low pass filter SW1, SW2: Switch

VR: Variable resistor CS: Control signal

PS: phase difference signal

The present invention uses a horizontal synchronization signal of a video signal as a reference frequency in a broadcast device of a television station or a video receiver such as a television receiver and a video cassette recorder that receives a television broadcast signal, such as an oscillation signal of a local oscillator. A frequency stabilization circuit of a reference signal using a horizontal synchronization signal of a video signal for stabilizing frequencies of various reference signals to be generated. In general, when generating a reference signal of a specific frequency is mainly used a crystal oscillator using the crystal piece as a vibrator. While the crystal oscillates stably in the high frequency band, the oscillation frequency is variable in response to changes in temperature and humidity, so that even if the surrounding temperature and crystals oscillate stably, dozens of PPMs (Parts Per A frequency deviation of about milliseconds is occurring. Therefore, the frequency of the reference signal generated by using a crystal piece in a video receiver such as a television receiver or a video cassette recorder that receives a television broadcast signal is different, and thus is unnecessarily fired to the outside from each device. Frequency deviation between spurious waves occurs, and high frequency interference is severely generated due to this frequency deviation, which greatly affects reception of broadcast signals and degrades screen quality.

The present invention has been made to solve the above-mentioned conventional problems, and the reference signal and phase generated by using a horizontal synchronization signal of a very small video signal with a frequency deviation of about 0.1 to 0.2PPM using cesium as a vibrator. By using the horizontal synchronization signal as the reference frequency to compare the signal, the frequency deviation is about 0.1 ~ 0.2PPM, which generates very little reference signal and can be applied to the equipment of NTSC, PAL, and SECAM systems without changing the circuit. The purpose of the present invention is to provide a frequency stabilization circuit which will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a frequency stabilization circuit of the present invention. As shown therein, a synchronization signal separator 1 for separating a synchronization signal from an image signal and a horizontal signal triggered in accordance with the output signal of the synchronization signal separator 1 are horizontal. A horizontal synchronous re-oscillator 2 for generating a pulse signal at a period of the synchronous signal, a horizontal synchronous divider 3 for dividing an output signal of the horizontal synchronous re-oscillator 2 and outputting it as a standard signal, and oscillating a reference signal A variable generator (4) for generating a signal, a reference signal divider (5) for dividing the oscillation signal of the variable oscillator (4), and output signals of the divider (5) to NTSC, PAL and SECAM methods. The phase difference signal PS is output by comparing the phases of the variable divider 7 for variable division with the control of the selector 6 and the output signals of the horizontal synchronous divider 3 and the variable divider 7. And depending on whether or not the output signal of the horizontal synchronous divider (3) A phase comparator 8 for outputting a tack control signal CS and a switch SW1 for selectively outputting a reference voltage set to the phase difference signal PS and the variable resistor VR while being switched according to the selection control signal CS. (SW2) and a low pass filter (9) for controlling the oscillation frequency of the variable oscillator (4) by filtering the output signal of the switch (SW1) (SW2).

In the drawing description of FIG. 1, reference numeral B + denotes a power source. The frequency stabilization circuit of the present invention configured as described above receives an image and a horizontal synchronous signal, an equalization signal and a vertical synchronous signal as shown in (a) of FIG. 2 while a power supply B + is applied. When the synchronous signal separator 1 separates the synchronous signal from the input image signal as shown in (b) of FIG. 2, the synchronous signal regenerator 2 is triggered according to the output synchronous signal. Here, the horizontal synchronous re-oscillator 2 uses a general mono-multi, etc., to be triggered at the rising edge of the synchronous signal separated by the synchronous signal separator 1, and the duty ratio is 1 /. When set to 2 or more, the horizontal synchronous re-oscillator 2 generates a pulse signal at a period of the horizontal synchronous signal as shown in (c) of FIG.

Thus, the pulse signal of the horizontal synchronizing signal cycle output by the horizontal synchronizing re-oscillator 2 is divided into a predetermined value in the horizontal synchronizing divider 3 as shown in (d) of FIG. 2, and the phase comparator 8 It is input as a signal of standard frequency to generate a reference signal. The variable oscillator 4 oscillates to generate a reference signal of a predetermined frequency, and the generated reference signal is divided into a predetermined value by the reference signal divider 5 and the NTSC method, PAL method, and SECAM method by the variable counter 7. By the control of the selector according to the present invention, a predetermined value is dispensed as shown in (e) of FIG. 2 and input to the phase comparator 8. Then, the phase comparator 8 determines the presence or absence of the output signal of the horizontal synchronous divider 3 to output the control signal CS, and the output signal of the horizontal synchronous divider 3 and the variable divider 7. The phase difference signal PS is output by comparing the phases.

Here, assuming that there is an output signal of the horizontal synchronous divider 3, the phase comparator 8 outputs a high potential control signal CS so that the movable terminal of the switches SW1 and SW2 has one fixed terminal a1. Since it is connected to (a2), the phase difference signal output by the phase comparator 8 is filtered through the switch SW1 and filtered by the low pass filter 9 and then output to the variable oscillator 4. At this time, when the phase of the output signal of the horizontal synchronous divider 3 is faster than the phase of the output signal of the variable divider 7, it means that the oscillation frequency of the variable oscillator 4 is low. As shown in (f) of FIG. 2, a phase difference signal PS having a positive pulse width is output in proportion to the phase difference of the two signals, and the output phase difference signal PS is used to switch the switch SW1 and the low pass filter 9 to each other. Through the input to the variable oscillator 4 is to increase the reference signal oscillation frequency of the variable oscillator (4).

When the phase of the output signal of the horizontal synchronous divider 3 is slower than the phase of the output signal of the variable divider 7, it means that the oscillation frequency of the variable oscillator 4 is high. As shown in (g) of FIG. 2, a phase difference signal PS having a negative pulse width is output in proportion to the phase difference of the two signals, and the output phase difference signal PS is connected to the switch SW1 and the low pass filter 9. Through the input to the variable oscillator 4 is to reduce the reference signal oscillation frequency of the variable oscillator (4).

The frequency stabilization circuit of the present invention adjusts the division values of the horizontal synchronous divider 3, the reference signal divider 5, and the variable divider 7 to be applied to the PAL and SECAM methods as well as the NTSC method. It will be described in detail that can generate a reference signal. In general, the NTSC-M method adopted by countries such as the Republic of Korea, the United States, and Japan, and the PAL-M method adopted by Brazil have a gap between an image carrier frequency and an audio carrier frequency, and an audio carrier frequency and an image carrier frequency = 4.5. MHz. The NTSC-M and PAL-M methods are designed to carry audio signals and signals at the position of the integer horizontal sync signal where the harmonics occur the least, that is, the position of the 286th horizontal sync signal. The frequency of the horizontal synchronization signal is given by the following equation (I).

Dividing Equation (I) by 4.5 to make 1 MHz as a reference unit gives Equation (II).

In addition, the PAL-N method of 4.5MHz, the PAL-N method of 4.5MHz, the PAL-B, PAL-G, PAL-H and SECAM-B method of 5.5MHz, the PAL-I method of 6.0MHz, The 6.5 MHz PAL-D, SECAM-D, SECAM-K, SECAM-K1, SECAM-K2, SECAM-E and SECAM-L types are used for the voice carriers at the 288th, 352th and 416th horizontal sync signals, respectively. The frequency of the horizontal synchronous signal of each system is 15625 Hz as shown in the following equation (III).

In order to make Equation (III) above 1 MHz as a reference unit, each side is divided into 4.5, 5.5, 6.0, and 6.5 as shown in Equation (IV) below.

Dividing both sides of Equation (II) and (IV) by 9 converts into Equation (V) and Equation (VI) below.

According to the above equations (V) and (VI), the horizontal synchronous divider 3 divides the horizontal synchronous signal by 1/9 to output the frequency stabilization circuit of the present invention, and the reference signal divider 5 Divides the reference signal and outputs it at 1 MHz, and when the frequency of the horizontal synchronous signal is 15734.26573 Hz, the variable divider 7 divides and outputs 1/572 = 1 / (143 × 4) and horizontally. When the frequency of the synchronization signal is 15625 Hz, the variable divider 7 divides and outputs 1/576 = 1 / (144 × 4) to output the horizontal synchronous divider 3 and the variable divider 7. Since the frequency of the signal is the same, it can be applied to both NTSC, PAL and SECAM.

As described in detail above, the present invention generates a reference signal by using a horizontal synchronization signal in an image signal having a very low frequency deviation of about 0.1 to 0.2 PPM. Thus, for example, each video apparatus such as a television receiver and a video cassette recorder has an internal structure. The frequencies of the local oscillation signals, which are the reference signals generated by, all match, which makes it easy not only to remove the crosstalk modulation caused by the difference in radio wave strength, but also to eliminate the high frequency interference. It is stable and accurate, which improves the screen quality and reduces the production cost of the device by eliminating the need for automatic frequency control circuit, fine tuning circuit, horizontal synchronous oscillator and vertical synchronous oscillator. .

Claims (2)

A synchronizing signal separator 1 for separating the synchronizing signal from the video signal, a horizontal synchronizing re-oscillator 2 which is triggered according to an output signal of the synchronizing signal separator 1 and generates a pulse signal at a period of the horizontal synchronizing signal; A horizontal synchronous divider 3 which divides the output signal of the horizontal synchronous re-oscillator 2 and outputs it as a standard signal, a variable oscillator 4 which oscillates to generate a reference signal, and an oscillation signal of the variable oscillator 4 A reference signal divider 5 for dividing the variable, a variable divider 7 for dividing the output signal of the divider 5 under the control of the selector 6 according to the NTSC method, the PAL method and the SECAM method; The phase control signal PS is output by comparing the phases of the output signals of the horizontal synchronous divider 3 and the variable divider 7 and the selection control signal according to the presence or absence of the output signal of the horizontal synchronous divider 3. A phase comparator 8 for outputting (CS) is switched in accordance with the selection control signal CS. And the switch (SW1) (SW2) for selectively outputting the reference voltage set by the phase difference signal (PS) and the variable resistor (VR) and the output signal of the switch (SW1) (SW2) by filtering the variable oscillator (4) Reference signal frequency stabilization circuit using a horizontal synchronous signal of the video signal, characterized in that consisting of a low-pass filter for controlling the oscillation frequency of the video signal. The horizontal synchronous divider (3) divides the horizontal synchronous signal by 1/9, and the reference signal divider (5) divides the reference signal to output at 1 MHz, and the variable divider (7). ) Is a reference signal frequency stabilization circuit using horizontal synchronization signal of the image signal, characterized in that when the frequency of the horizontal synchronization signal is 15734.26573Hz and 15625Hz divided into 1/572 and 1/576.

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