JPH10312182A - Video signal discriminating circuit for picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a discriminant likelihood by counting fundamental clocks being in one horizontal period of an input video signal, counting horizontal synchrinizing pulses being in one vertical period of the input video signal and discriminating the kind of the input video signal by these measured values. SOLUTION: A reference oscillator 11 generates fundamental clock pulses having a frequency Fr sufficiently larger than the maximum value of horizontal frequencies of plural input video signals made to be objects. A first counter 12 counts the fundamental clock pulses between a horizontal synchronizing pulse and a next horizontal synchronizing pulse of the input video signal. A second counter 13 counts horizontal synchronizing pulses of the signal between a vertical synchronizing pulse and a next vertical synchronizing pulse of the signal. A control part 7 discriminates the kind of the input video signal by these measured values to perform necessary controls with respect to a processing circuit 2. Thus, horizontal and vertical frequencies or periods of the input video signal are measured with an accuracy higher than that of the conventional practice and, as a result, the kind of the input video signal is securely discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal discriminating circuit for an image display device, and more particularly to a technique for improving the accuracy of discrimination.

[0002]

2. Description of the Related Art As shown in FIG. 3, a video signal from a personal computer or the like has a horizontal frequency Fh and a vertical frequency Fv which differ depending on the dot configuration of one screen. Further, even with the same dot configuration, there is a slight difference in their synchronization frequencies due to differences between manufacturers and the like. However, in an image display apparatus using, for example, a color liquid crystal element (LCD) used in a personal computer or the like, since the vertical and horizontal dot configuration of one screen and the standard horizontal and vertical frequencies are determined, The video signal discriminating circuit 1 discriminates the type of the video signal from the horizontal and vertical synchronizing signal frequencies of the input video signal and converts the type into a standard synchronizing signal (frequency) of the image display device. It is performed under the control of the signal discriminating circuit 1.

In a conventional video signal discriminating circuit 1, horizontal and vertical synchronizing signals of an input video signal are input to an F / V converter 5, and voltages Vh and Fv corresponding to respective frequencies Fh and Fv are output.
Vv is taken out, these voltages are input to the A / D converter 6 and converted into digital data Dh and Dv, and the control unit (C
PU) 7. The CPU 7 converts the data Dh and Dv into R
The type of the input video signal is determined by comparing the horizontal and vertical frequencies of a plurality of types of video signals to be written in the AM 8 in advance, and the conversion processing of the synchronization signal of the processing circuit 2 is controlled. The CPU 7 decodes and executes the system program stored in the ROM 9 to perform the determination and the control operation.

[0004]

In the conventional video signal discriminating circuit 1, after horizontal / vertical synchronizing signals are subjected to F / V conversion, their voltage values are A / D converted, and the horizontal frequency is calculated from the obtained digital values. And the vertical frequency are determined to determine the type of the input video signal. There is a limit to the accuracy of the F / V converter 5 and the A / D converter 6 which can be used at normal prices, and the measured horizontal frequency Fh and vertical frequency Since the accuracy of Fv cannot be sufficiently obtained, there is a problem that the accuracy of determining the type of the input video signal is low.

Since the analog voltage is interposed in the middle of the discriminating circuit, the measured values of the horizontal frequency and the vertical frequency fluctuate due to the influence of power supply fluctuation and noise, and there is a problem that the discrimination accuracy is reduced. SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems and improve the discrimination accuracy.

[0006]

[Means for Solving the Problems]

(1) According to the first aspect of the invention, an arbitrary one type of video signal is input to an image display device from a plurality of types of video signals having different horizontal frequencies or vertical frequencies, and the type of the input video signal is determined. The present invention relates to a video signal determination circuit of an image display device. In particular, a reference oscillator for generating a basic clock pulse having a frequency sufficiently higher than the maximum value of the horizontal frequency of a plurality of types of video signals, and counting the basic clock pulses of 1H (one horizontal period) of the input video signal. A first counter, a second counter that counts horizontal synchronization pulses in one vertical period of the input video signal, and a control unit that determines the type of the input video signal from the measured values of the first and second counters are provided.

(2) In the second aspect of the present invention, in the above (1), the reference oscillator is controlled by the control unit, and performs the oscillation operation only for a predetermined period necessary for determining the type of the input video signal.

[0008]

FIG. 1 shows an embodiment of the present invention, and FIG.
The same reference numerals are given to the portions corresponding to and the description will be omitted. According to the present invention, the horizontal and vertical frequencies are converted into analog voltages once, and the analog voltages are converted into digital values again.
h = 1 / Fh) and a vertical period (Tv = 1 / Fv) are measured by a counter.

Reference numeral 11 denotes a reference oscillator, which has a frequency Fr (period is Tr) whose frequency is sufficiently larger (for example, about 100 to 1000 times) than the maximum value of the horizontal frequency (FIG. 3) of a plurality of target input video signals. Generate a clock pulse. 1
Reference numeral 2 denotes a first counter which counts 1H (one horizontal period Th) of the input video signal, that is, the basic clock pulse between the horizontal synchronization pulse and the next horizontal synchronization pulse as shown in FIGS. 2A and 2B. Assuming that the count value is n, there is the following relationship.

N = Th / Tr = Fr / Fh (1) ∴Th = n × Tr = n / Fr (2) Reference numeral 13 denotes a second counter, as shown in FIGS. 2C and 2D. The vertical synchronization period Tv of the input video signal, that is, the horizontal synchronization pulse of the input video signal between the vertical synchronization pulse and the next vertical synchronization pulse is counted. Assuming that the count value is m, there is the following relationship.

M = Tv / Th = Fh / Fv (3) ∴Tv = m × Th = m × n × Tr = m × n / Fr (4) First and second counters Count values n and m of the control unit (CPU)
7. The control unit 7 calculates Fh = 1 / Th = Fr / n (2 ′) according to the equation (2) as necessary. Further, the control unit 7 calculates Fv = 1 / Tv = Fh / m = Fr / mn (5) from Expression (4) as necessary. The control unit 7 calculates the calculated horizontal frequency F
hd and the vertical frequency Fvd are compared with the horizontal frequency Fh and the vertical frequency Fv of FIG. 3 stored in the RAM 8 to determine the type of the input video signal and perform necessary control on the processing circuit 2.

Since m = Fh / Fv and n = Fr / Fh are known for a plurality of types of video signals of interest, these data are stored in the RAM 8 in advance, and
The control unit 7 may determine the type of the video signal by directly comparing the count values n and m with the corresponding data stored in the RAM 8 without calculating the horizontal frequency Fhd or the vertical frequency Fvd.

Under the influence of the reference clock of the reference oscillator 11, L
If the noise appears on the screen of the CD4, the control unit 7
It is desirable to control the reference oscillator 11 to perform the oscillation operation only for a predetermined period necessary for determining the type of the input video signal.

[0014]

According to the present invention, the horizontal period Th and the vertical period Tv are not counted by the counter without using the F / V converter and the A / D converter which have conventionally caused the low accuracy of the horizontal and vertical frequency measurement. In addition to measuring, as a counting pulse necessary for the measurement, 100 to 100 pulses from the horizontal frequency Fh and the vertical frequency Fv
The basic clock and the horizontal frequency having sufficiently large frequencies such as 1000 times are used. Therefore, the horizontal or vertical frequency or period of the input video signal can be measured with higher accuracy than before, and as a result, the type of the input video signal can be reliably determined.

Since an analog voltage that is easily affected by power supply fluctuation and noise is not interposed in the middle of the determination circuit as in the related art, a determination circuit that is resistant to power supply fluctuation and noise can be obtained. According to the present invention, since a less expensive counter and reference oscillator are used without using a conventional F / V converter or A / D converter, a more economical discriminating circuit can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a timing chart of a main part of FIG. 1;

FIG. 3 is a diagram showing horizontal and vertical frequencies and the like of a plurality of types of video signals to be processed;

FIG. 4 is a block diagram of a video signal discriminating circuit of a conventional image display device.

Claims (2)

[Claims] 1. An image display apparatus comprising: an image display device that receives an arbitrary one of a plurality of types of video signals having different horizontal frequencies or vertical frequencies and determines the type of the input image signal; In the signal discriminating circuit, a reference oscillator for generating a basic clock pulse having a frequency sufficiently higher than the maximum value of the horizontal frequencies of the plurality of types of video signals, and counting the basic clock pulses of 1H (one horizontal period) of the input video signal. A first counter, a second counter that counts horizontal synchronization pulses in one vertical period of the input video signal, and a control unit that determines a type of the input video signal based on measured values of the first and second counters. A video signal discriminating circuit of an image display device, characterized by comprising: 2. The method according to claim 1, wherein the reference oscillator comprises:
A video signal discriminating circuit, controlled by the control unit, to perform an oscillation operation only for a predetermined period necessary for discriminating a type of an input video signal.