JPH0759042B2 - Blanking signal generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a blanking signal generating circuit useful when, for example, a baseband color difference signal is encoded to form a composite video signal or the like.

[Outline of Invention]

The blanking signal generating circuit of the present invention is triggered by the synchronizing signal when forming the horizontal blanking signal, the vertical blanking signal, and the burst flag signal indicating the color burst period from the synchronizing signal separated from the luminance signal. A pulse generator composed of an analog circuit and a counter for counting a reference signal are used.

Therefore, the number of circuit elements can be significantly reduced as compared with the conventional blanking signal generation circuit.

[Conventional technology]

In some color displays of personal computers, video games, electronic cameras, and the like, signal processing is performed in a state in which a luminance signal and a color signal forming an image signal are separated in a baseband band.

In such an image signal, for the luminance signal Y, the color information is, for example, the color difference signals (RY) in the base band and (B-
Y) will be recorded and reproduced.

Therefore, when forming an NTSC composite video signal from such a signal, the color difference signals (RY) and (BY) are quadrature-phase modulated by the color subcarrier frequency and converted into a carrier color signal. Then, signal processing to be superimposed on the luminance signal is performed.

In this case, when the reproduced color difference signal is converted into the carrier color signal and superimposed on the luminance signal, the carrier color signal modulated by noise is superimposed during the blanking period of the image signal, and the S of the composite video signal is superimposed. / N ratio deteriorates.

Therefore, conventionally, a blanking signal generating circuit corresponding to a horizontal blanking period, a vertical blanking period and a color burst period is used, and a carrier color signal and a color burst are superimposed only on a predetermined portion of a luminance signal. Signal processing was being done.

FIG. 4 shows a conventional example of such a blanking signal generating circuit. Reference numeral 1 is a sync separation circuit for extracting a sync signal portion from a luminance signal Y, and 2 is vertical sync extraction for forming a vertical sync signal from the sync signal. Circuit 3 is a voltage controlled oscillator (VCO)
4 is a phase comparator for controlling the oscillating frequency, which performs phase comparison of the horizontal synchronization separated from the signal indicating one horizontal period obtained from the counter logic circuit 5.

Reference numeral 6 is a reference signal oscillator for forming the color subcarrier f _SC. The output (14.32 MHz) of this reference signal oscillator 6 is divided by, for example, 1/4 by the next counter 7 and divided into two with 90 ° phase difference. The color subcarrier f _SC (3.58MHz) is output.

As described above, the conventional blanking synchronization signal generation circuit first sets the phase comparator so that the oscillation frequency f ₀ of the voltage variable oscillator 4 becomes, for example, an integral multiple of the horizontal oscillation frequency (1H), for example, 260 times. 3. and counter logic circuit 5
The signal pulse for blanking is counted by controlling by the PLL circuit and processing the count output of the counter logic circuit by the logic circuit.

That is, as shown in the standard video signal waveform diagram of FIG. 5, the horizontal sync signal of 0.075H is output from the HD terminal, and the BF
A burst flag signal indicating a color burst signal period of 0.119H is output from the terminal, a signal indicating a horizontal blanking period of 0.18H is output from the H · BLK terminal, and a signal indicating a vertical blanking period is output from the V · BLK terminal. To do.

Then, when the color difference signal is modulated by the chrominance carrier signal output from the counter 7 to form the carrier chrominance signal and then superimposed on the luminance signal, by the signal indicated by the horizontal blanking period and the signal indicating the vertical blanking period. Try to suppress the color carrier signal.

Further, the burst flag causes the color subcarrier to be superimposed on the luminance signal only during this signal period to form a composite video signal.

[Problems to be solved by the invention]

However, in the conventional blanking signal generating circuit, the oscillation frequency of the voltage variable oscillator 4 is set to the counter logic circuit 5
Since various synchronizing signals are output at predetermined points in the video signal period while counting by
Since it is necessary to increase the oscillation frequency f ₀ of the voltage variable oscillator in order to output the synchronization signal with a precision of about 6H in a timely manner, the number of counting stages of the counter logic circuit 5 and the number of logic elements are increased, and high speed There was a problem that things were needed.

In addition, there is a problem that the circuit becomes complicated in order to make the PLL circuit stable and the cost increases.

The present invention has been made to alleviate such a problem, and provides a signal generating circuit for blanking in which the number of circuit elements is reduced by using an analog synchronizing signal generating circuit.

[Procedure for solving problems]

The blanking signal generating circuit of the present invention uses a pulse generator using a color burst flag signal (BF), a horizontal synchronizing signal (HD) with a time constant, and a vertical synchronizing signal using a pulse generator with a low-pass filter. The signal (H.BLK) indicating the horizontal blanking period, which requires a high degree of accuracy, is generated by resetting the counter for dividing the signal from the reference oscillator by the horizontal synchronizing signal.

[Action]

The horizontal sync signal, which is separated from the luminance signal and is close to the falling point of the sync signal, and the burst flag signal, which indicates the color burst signal period, include a pulse generator having an appropriate time constant, such as a monostable multivibrator. Formed using. In addition, high accuracy is required for the signal indicating the horizontal blanking period which is relatively far from the falling edge of the sync signal, and only this signal requires a reference signal such as a crystal oscillator for a counter that is reset by the horizontal sync signal. Supply and form.

Therefore, the number of blanking signal generating circuit elements can be reduced as compared with the conventional one.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. 10 is a sync signal separating circuit for separating a sync signal from a luminance signal Y,
Reference numeral 11 is a first pulse generator for outputting a horizontal synchronizing signal pulse (HD) at a predetermined interval every 1H (1 horizontal period), for example, one pulse generator triggered by the falling point from the synchronizing signal separating circuit 11. It is formed of a shot multi, a reference voltage source, a comparator and the like.

Reference numeral 12 is a second pulse generator which is also triggered by the signal from the sync signal separation circuit 10. This second pulse generator 12 forms a signal corresponding to the color burst period, that is, a burst flag signal BF. Is.

Reference numeral 13 is a low-pass filter that integrates the separated sync signals, and detects a vertical sync signal portion having a wide pulse width, as found in, for example, a circuit that forms a vertical sync signal of a television.

14 is the first for counting the color subcarriers in the case of this embodiment.
The counter is configured to be reset every 1H and generates an output pulse, that is, a horizontal blanking signal H · BLK between count values N ₁ and N ₂ as described later. Reference numerals 15 and 16 denote a reference oscillator and a counter for generating a color subcarrier as in the above-mentioned conventional example, and output a color subcarrier frequency f _sc with a 90 ° phase difference at the output.

Reference numeral 17 denotes a second counter which counts horizontal synchronizing signals and forms a vertical blanking signal for each horizontal synchronizing signal for one field, for example.

The operation of the blanking synchronizing signal of the present invention will be described below with reference to the waveform diagram of FIG.

The sync signal SS separated from the luminance signal by the sync separation circuit 10 is input to the first and second pulse generators 11 and 12 and the low-pass filter 13.

The first pulse generator 11 generates a ramp wave as shown by M ₁ by being triggered by the falling point t ₁ of the synchronizing signal SS. Then, when the ramp wave M ₁ reaches the reference voltage E ₁ , it is detected to form the horizontal synchronizing signal HD.

The second pulse generator 12 is also triggered at the falling point of the sync signal SS to generate the ramp signal M ₂ .

Then, when the ramp wave M ₂ reaches the reference voltages E ₂ and E ₃ , a burst flag pulse (BF) is output.

In this case, for example, a monostable multivibrator is used to output the ramp signal, and the output pulse width has a period T.
Is set to be longer than the 1 / 2H period and shorter than the H period. Then, it will not respond to the 1 / 2H period synchronizing signal shown by the dotted line inserted in the vertical blanking period, and if the reference voltages E ₁ , E ₂ , and E ₃ are set to predetermined values, One horizontal synchronizing signal HD and the burst flag signal BF for color burst blanking can be obtained every 1H period.

A well-known vertical sync signal VD is obtained by integrating the sync signal input to the low-pass filter 13.

Then, when the second counter 17 counting the horizontal synchronizing signal HD by the vertical synchronizing signal VD is reset, the vertical blanking signal V · for setting the vertical blanking period is set.
BLK can be output from the second counter 17.

The horizontal blanking synchronization signal H · BLK has a predetermined count value, for example, a pulse waveform which rises at N ₁ and falls at N ₂ while counting the color carrier f _SC output from the counter 16 by the first counter 14. It can be obtained by forming.

In this case, the counting start point can be controlled by resetting the first counter 14 by the horizontal synchronizing signal HD.

Since the color carrier frequency f _SC is set to 3.58 MHz with high accuracy by the reference signal oscillator 15, the phase error of the horizontal blanking signals H · BLK never exceeds 0.28 μS, and the NTSC TV system The condition of the error range (1 to 1.5 μS) specified in 1 can be sufficiently satisfied.

The horizontal synchronizing signal HD and the burst flag signal BF output from the first and second pulse generators formed by the analog circuit are output close to the falling point of the synchronizing signal SS. It is possible to output with a fairly high accuracy even by a constant circuit, and it is easy to satisfy the error range conditions regulated by the NTSC TV waveform.

FIG. 3 shows a concrete circuit example of the first and second pulse generators 11 and 12, where 21 is a monostable multivibrator which is triggered at the falling point of the synchronizing signal, and 22 is a monostable multivibrator. A ramp signal generator that generates a ramp voltage according to the output pulse of the stable multivibrator, 23 and 24 are level comparators, and 25 is an ex-OR circuit.

The output pulse width of the monostable multivibrator is set between 1 / 2H and H, and the ramp signal generator 22 generates a ramp signal that rises during this pulse width. Different reference voltages E ₁ and E ₂ are input to the level comparator, so if these reference voltages E ₁ and E ₂ are set to predetermined values, the burst flag corresponding to the horizontal sync signal HD and the color burst signal period described above will be generated. You can set the rising and falling points of the signal.

Then, the ex-OR circuit 25 outputs a pulse signal corresponding to the time difference at the rising time.

In the embodiments of the first and second pulse generators, the blanking signal is formed by the time constant for forming the ramp signal and the reference voltage value. Is close to the falling point of the synchronizing signal, the rising error thereof is extremely small, and the analog circuit can provide sufficient accuracy.

Needless to say, other types of analog pulse generators such as a blanking oscillator circuit may be used as the first and second pulse generators.

The blanking signal generating circuit of the present invention is a color difference signal (R-
It goes without saying that it can be used for blanking the baseband color signals R, G, B, etc. in addition to Y) and (BY).

〔The invention's effect〕

As described above, the blanking signal generation circuit of the present invention can drastically reduce the number of circuit elements as compared with the conventional blanking signal generation circuit, and can reduce the cost of the circuit and at the same time There is an effect that a synchronization signal for blanking with high accuracy can be output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a blanking signal generating circuit of the present invention, FIG. 2 is an operation waveform diagram of FIG. 1, and FIG. 3 is a circuit diagram showing an example of a pulse generator. FIG. 4 is a block diagram of a conventional blanking signal generating circuit, and FIG. 5 is a waveform diagram of a television signal. In the figure, 10 is a sync signal separation circuit, 11 and 12 are first and second pulse generators, 13 is a low-pass filter that serves as an integration circuit, and 14 and 1
Reference numeral 7 indicates the first and second counters.

Claims (1)

[Claims] 1. A first and second pulse generator that outputs a pulse having a predetermined pulse width in synchronization with a synchronization signal separated from a luminance signal; a low-pass filter to which the synchronization signal is input; A first counter reset by a horizontal sync signal output from a first pulse generator and counting a reference frequency; and a first counter reset by a vertical sync signal output from the low pass filter from the first pulse generator. A second counter for counting the output horizontal synchronizing signal, forming a burst flag signal from the second pulse generator, and generating a vertical blanking signal from the output of the first counter. A blanking signal generating circuit, which is configured to generate a horizontal blanking signal from the output of the second counter.