JPH0124473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video signal processing device for use in television receivers, video tape recorders, etc., for delaying video signals by one horizontal scanning period.

Conventional configuration and problems There is a comb filter as a means for separating a luminance signal and a color signal from an NTSC color television video signal (hereinafter referred to as an NTSC color signal), as shown in Figure 1. It is configured as shown in . In FIG. 1, 1 is a 1 horizontal period (1H) delay circuit having a band characteristic as shown in characteristic 7;
2 is a subtraction circuit, 3 is a bandpass filter (BPF) having band characteristics similar to characteristic 7, 4 is an addition circuit,
5 is a luminance signal (Y signal) output terminal, and 6 is a color signal (C signal) output terminal. In such a configuration,
Since the phase of the color subcarrier in the NTSC color signal is inverted every 1H, the subtraction circuit 2 outputs a signal with twice the amplitude of the input signal. That is, if the NTSC color signal is a single sine wave signal represented by Esinωt, the signal after passing through the 1H delay circuit 1 becomes Esinω(t+T _H ). T _H is one horizontal period.

Therefore, the output E _C of the subtraction circuit 2 that subtracts these from each other is E _C =Esinωt−Esinω(t+T _H )=E{(1−cosωT _H )sinωt −sinωT _H cosωt}, which is E _C =E√(1- _H ) ² + ² _H e(ωt
−) is expressed as Therefore, the amplitude characteristic of the output E _C is E _C = E√1−2 _H + ² _H + ²
_H =√2√1− _H =2E｜sinω／2T _H ｜. Here, since ω=2π, T _H 1/ _H , E _C =2E|sin/ _H π|. As is clear from this equation, when / _H = n (n is a positive integer), E _C = O, and when / _H = 2n + 1/2, E _C = 2E. Therefore, the 1H delay circuit 1 and the subtraction circuit 2 form a filter exhibiting comb-shaped characteristics as shown by the solid line in FIG. 2A.

By the way, the color signal C in the NTSC color signal
The spectrum of the luminance signal Y is shown by diagonal lines in FIG. 2, and the spectrum of the luminance signal Y is shown by dotted lines. Therefore, only the color signal C is extracted by the subtraction circuit 2 of this comb filter. The bandpass filter 3 is used to limit the leakage of signals other than the passband shown in characteristic 7 that are not delayed by 1H. Therefore, only the separated color signal C is taken out to the output line 6.

On the other hand, only the luminance signal Y is taken out to the output line 5 of the adder 4. This is because the phase of the color subcarrier is inverted every 1H, so when the 1H delayed and undelayed signals are added together, the color signal C is canceled out and only the luminance signal Y remains.

Expressing this in a formula, the output E _Y of the adder 4 is E _Y =Esinωt+Esinω(t+T _H )=E{(1+cosωT _H
) sinωt＋sinωT _H cosωt} = E√(1+ _H ) ² + ² _H e(ω
t−). Therefore, the amplitude characteristic of the output E _Y is E _Y =√2E√1+ _H =2E|cosω/2T _H |. Here, from ω = 2π, T _H = 1/ _H , E _Y = 2E | cos / _H π |, when / _H = n, E _Y = 2E, and when / _H = 2n + 1/2, E _Y =0.

Therefore, the 1H delay circuit 1 and the adder circuit 4 are
A filter with comb-shaped characteristics as shown in Figure B is formed. As is clear from FIG. 2, in such a comb filter, only the luminance signal Y is taken out and the color signal C is removed.

The luminance signal Y and chrominance signal C are separated based on the above principle, but in such a comb filter, the bandwidth and group delay characteristics of the 1H delay circuit 1 pose problems.

A glass delay line is usually used as the 1H delay circuit 1, but its passband width is at most about 30% of the center frequency, and as shown in characteristic diagram 7 in Figure 1, For a device with a frequency of 3.58MHz, securing a passband width of 1MHz is the maximum. However, in the case of NTSC color signals for broadcasting, even if the band of the color signal itself is in the baseband state,
The bandwidth is approximately 1.5MHz, and when the color subcarrier is modulated, the bandwidth is approximately 3MHz. However, NTSC
Color signals are transmitted using the vestigial sideband method in which the upper sideband of the color subcarrier is removed, so in reality, the band from (3.58 + 0.5) M _Z to (3.58 - 1.5) MHz is sufficient. Become.

In this way, since the 1H delay circuit 1 cannot have a sufficient band, the band of the color signal obtained on the output line 6 is limited, and in the adder 4, the color signal is not canceled over the entire band, but is partially canceled out. In addition, color signal components outside the band of the 1H delay circuit 1 remain in the luminance signal obtained on the output line 5.

Furthermore, since the 1H delay circuit 1 has band characteristics, the group delay characteristics at the ends of the pass band and near the center are different. Therefore, even if the delay time is just one horizontal period near the color subcarrier frequency at the center of the band (near 3.58MHz), the delay time is just one horizontal period at frequencies near the edge of the band. Instead, the pole point of the comb-shaped filter is slightly shifted, resulting in poor performance in separating the luminance signal and color signal.

For the reasons mentioned above, it is necessary to design the 1H delay circuit 1 with as much bandwidth as possible.

In view of these points, a comb filter as shown in Fig. 3 using a broadband ultrasonic 1H delay line has been put into practical use for high-grade YC separation circuits. Here, 8 is
NTSC color signal input terminal 9 is an amplitude modulator that accepts NTSC color signals with a band of approximately 4MHz.
Using the carrier wave from the 30MHz oscillator 10, characteristic 1
It is converted to the 30MHz band as shown in the spectrum diagram of No.8. Reference numeral 11 denotes an ultrasonic 1H delay line, which has a band characteristic as shown by characteristic 12. As mentioned above, the ultrasonic 1H delay line 11 is a bandpass with a bandwidth of about 10 MHz, since the current technology limit is to pass a band of about 1/3 of the center frequency. Show characteristics. This 1H delay line 11
The output signal of 1 is detected by the demodulator 13 to obtain a 1H delayed NTSC color signal,
A luminance signal Y can be obtained on the 6th line, and a chrominance signal C can be obtained on the output line 17 of the subtracter 14.

By using such a wideband 1H delay circuit, a comb filter with good Y/C separation characteristics can be formed.

However, such an ultrasonic 1H delay line 1
1 has a problem in that its absolute delay time changes because it expands or contracts depending on the temperature. Now, if we assume that there is a delay time change of 3ppm/°C, then in 1H it will be 63.556μs x 3x per 1°C.
10 ^-6 = 0.19ns 0.2ns delay time change, 0℃
For a temperature change of ~40°C, there will be a change of 0.2ns x 40 = 8ns. When the delay time changes by 8ns,
In the vicinity of 3.58MHz, there is a deviation of 8/279×360≒10.3° for one period of 3.58MHz, 279ns, and from the above equation, E _C = 2E _C | sin10.3° | = 2E _C × 0.18, and with a comb filter. Up to 18% of the color signal C in the luminance signal Y, which should have been removed, remains, and the effect of the comb filter is greatly degraded.

Normally, when using a comb filter for the purpose described below, the permissible limit for color signals remaining in the luminance signal is approximately -40 dB (1/100).
Converting this into delay time deviation, sinx ⁰ = 1/100 becomes x = 35', and converting this into delay time, 35/60 x 1/360
× 279 = 0.45ns. Therefore, if the usage range of the ultrasonic 1H delay line is from 0℃ to 40℃, then per 1℃
The delay time deviation must be suppressed to 0.45/40=0.011ns. This is a value that is extremely difficult to achieve with current ultrasonic delay lines.

Furthermore, in an ultrasonic delay line, the amount of attenuation may vary depending on the temperature as well as the delay time variation.
In that case, even if the delay time is correctly matched, the amount of leakage of the color signal C will naturally increase. In other words,
In order to extremely suppress the amount of color signal leakage in the luminance signal, it is also necessary to suppress amplitude fluctuations.

Now, a device that separates an NTSC color signal into a luminance signal Y and a color signal C, double-tons the color signal, performs recording, playback, transmission, etc., and then combines it again and converts it into an NTSC color signal. For example, in the case of a video tape recorder, if a comb filter separates an NTSC color signal into a luminance signal and a chrominance signal, and if the chrominance signal remains in the output luminance signal as described above, they are combined again later. When converting to an NTSC color signal, the added color signal and the remaining color signal have the negative effect of causing beats and distortion. Therefore, it is used as a comb filter.
The 1H delay line must be exactly equal to 1H of the input signal. However, as mentioned above, if the delay time or amplitude fluctuates depending on the ambient temperature, or conversely, if the time of one horizontal period of the input signal is slightly out of order, the color signal component in the luminance signal will naturally change. The amount of leakage will increase.

Purpose of the Invention The present invention solves such conventional disadvantages and provides a 1H
An object of the present invention is to provide a signal processing device that can always accurately delay a television video signal by one horizontal period even if a delay time or amplitude varies in a delay circuit.

Structure of the Invention In the present invention, a control signal is created by comparing the amplitude and phase of each burst signal of an input color television video signal and a signal delayed by a 1H delay circuit. It is configured to control the control circuit and the minute variable delay circuit, respectively. By doing this, it is possible to obtain a 1H delayed signal whose amplitude and delay time are accurately controlled for the input color television signal, and by using this, a comb-shaped signal with less leakage of color signal components in the luminance signal can be obtained. You can get a filter.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows a block diagram of a video signal processing apparatus according to an embodiment of the present invention. In the figure, 21 is
NTSC color signal input terminal, 22 is an amplitude modulator, and 23 is a 1H delay line. Note that this 1H delay line 23 is made shorter by the delay time of a minutely variable delay circuit 27, which will be described later. 24 is 1H delay line 2
3 is an amplifier that amplifies the attenuated modulation signal, 25 is a variable gain control circuit whose gain is controlled by an externally applied DC control voltage, 26 is a demodulator, and 27 is a delay time using an externally applied DC control voltage. 28 is an output terminal that outputs a signal delayed by 1H. 29 and 3
0 is a burst gate circuit that extracts a burst signal from the NTSC color signal before being delayed (original signal) and the NTSC color signal delayed by 1H (delayed signal), and 31 and 32 detect the amplitude of each burst signal. Amplitude detection circuit, 33 and 3
4 is a sample and hold circuit that samples and holds the peak voltage of each amplitude-detected burst detection output, and 35 is a sample and hold circuit that compares both of the sampled and held voltages to determine the difference in amplitude of the burst signal between the original signal and the delayed signal. It is an operational amplifier that generates a DC voltage according to the The calculation output is applied to the variable gain control circuit 25 as a control voltage for gain control, and the amplitude of the delayed signal is controlled so that the amplitude of the burst signal of the original signal and the delayed signal are always equal.

On the other hand, 36 indicates the phase of the burst signal of the delayed signal.
37 and 38 are limiter circuits that limit the amplitude of the burst signals of the original signal and the delayed signal to a constant value; 39 is a phase detection circuit that compares the phases of the two burst signals; 40 is a sample-and-hold circuit that samples and holds the output voltage of the phase-detected burst signal portion;
41 is a sample and hold circuit that samples and holds the output voltage of the non-signal portion other than the burst signal portion, and 42 is a sample and hold circuit that compares these two sampled and held voltages and generates a DC voltage corresponding to the voltage difference, that is, both burst signals. This is an operational amplifier that generates a DC voltage according to the phase difference between the two. The calculation output is applied to the minute variable delay circuit 27 as a control voltage for delay time control, and is controlled to accurately match the timing of the delayed signal and the original signal.

Next, amplitude control and delay time control in the apparatus will be explained in detail.

FIG. 5 shows the form of each signal in the case of amplitude control, where A shows the burst signal subjected to burst gate, B shows the amplitude detection output thereof, and C shows the sampling pulse.

FIG. 6 shows a specific circuit example of the amplitude control section, where 51 is an input terminal for the +B power supply, 52 is an input terminal for the burst signal of the extracted original signal, and 53 is the input terminal for the burst signal of the extracted delayed signal. . 55
and 56 are transistors constituting an emitter follower circuit, 56 is a Zener diode for applying a DC bias voltage to the burst signal to be detected, 57 and 58 are bias application resistors, 59 and 60 are detection diodes, 61, 6
2 is an analog switch turned on by the sample and hold pulse of FIG. 5C for sampling; 63 and 64 are capacitors for holding the peak value of the sampled detection voltage;
5 and 66 are field effect transistors (FETs) that constitute a source follower circuit for inputting the held voltage at high impedance and outputting it at low impedance, and 67 is a delay circuit that uses the burst detection output voltage of the original signal as input on the + side. an operational amplifier whose negative side input is the burst detection output voltage of the signal, 68;
69 is a resistor and a capacitor for determining the gain and time constant of the operational amplifier 67, and 70 is an output terminal for a control signal for controlling the amplitude of the delayed signal.

In this circuit, if the delayed signal undergoes some fluctuation and its amplitude increases, the voltage at the negative input of the operational amplifier 67 will become higher than the positive input, and as a result, the amplitude control signal will be output. The output of the terminal 70 decreases, and the gain is controlled by the variable gain control circuit 25 in FIG. 4 until the amplitude of the delayed signal becomes equal to the amplitude of the original signal.

Next, the phase control circuit 39 will be explained. FIG. 7 is a vector diagram showing the principle. A is the phase of the burst signal of the original signal, and this is taken as the reference position at 0°. At this time, if the burst signal of the delayed signal is delayed by exactly 1H,
Since the phase of the carrier wave signal of the color signal is inverted every 1H, the phase of the burst signal has a phase difference of 180° from that of the burst of the original signal. Therefore, the burst phase of the delayed signal is at the position shown in FIG.
However, since the burst signal is delayed by 90 degrees in the 90 degree phase shift circuit 36 in FIG. 4, it ends up having the phase shown in FIG. It turns out.

FIG. 8 shows the signal waveforms of each part, A is the two burst input waveforms of the phase detection circuit 39,
B is its output waveform. Since the phase detection circuit 39 is in principle a multiplier of two input signals, a frequency twice that of the original burst signal appears.
The average DC level will be 0 when the two inputs have an exact 90° phase difference, and the closer the phase difference is to 0°, the more positive it will be.
The closer it is to 180°, the more negative it becomes. Figure 8C shows the delayed signal.
It shows the DC level when it is slightly delayed from 1H, and as shown in Fig. 7, when the delayed signal is delayed, the phase difference between the two inputs of the phase detection circuit 39 approaches 0°, so as shown in Fig. 8C. As shown, a positive voltage appears at the position of the burst signal with respect to the other reference potentials. Therefore, this output signal is shown as 2 in D and E in the same figure.
By sample-holding using two sampling pulses, a voltage corresponding to the burst phase difference can be obtained. These two voltages are amplified by the operational amplifier 42 and used as a delay time control signal for the minute variable delay circuit 27, and if the two voltages are controlled so that they are always equal, the two burst signals shown in FIG. 7A and C are The phase can always be kept accurately at 90°.
In other words, the burst phases of the original signal and the delayed signal are exactly 180 degrees apart, which means that the delayed signal is exactly in time with the original signal.

FIG. 9 shows a specific circuit example, where 81 is a +B power supply input terminal, and 82 is a burst input terminal for a burst gated original signal 83 is a burst input terminal for a burst gated delayed signal. 84 is an input terminal of the minute variable delay circuit 27, to which the demodulated 1H delay output is added. 85 and 86 are 90° phase shift circuit 3
6 constitutes an inductance and a variable capacitor; 87 and 88 constitute transistors constituting an amplifier for the limiter circuit 38; 89 and 90 a group of diodes constituting the limiter circuit 38; 91 a phase detector; 92 and 93 two Resistors 94 and 9 for preventing interference between sample and hold circuits 40 and 41
5 is an analog switch for sampling,
They are made conductive by a sampling pulse shown in FIG. 8D applied at 96 and a sampling pulse shown at E applied at 97, respectively. 98 and 99 are capacitors that hold the sampled voltage, 1
00,101 is a FET that constitutes a source follower to receive the voltage with high impedance, 1
02 is an operational amplifier inputting the two sampled and held voltages, and 103 and 104 are resistors and capacitors for determining the gain and time constant, respectively. A control voltage limited to phase comparison is applied to the minute variable delay circuit 27 through the resistor 105. 106 and 107 are DC cut capacitors, 108 and 109 are variable capacitance diodes, and 11
0 is an inductance, and 111 is an output terminal of the minute variable delay circuit 27.

The minute variable delay circuit 27 includes the variable capacitance diodes 108 and 109 and the inductance 11 as described above.
0, the delay time changes depending on the control voltage applied through the resistor 105. Since the capacitance of the variable capacitance diodes 108 and 109 decreases as the applied DC voltage increases, the delay time decreases and the delayed signal advances.

As explained in the example of FIG. 8, if the delayed signal is delayed for some reason, the operational amplifier 10
The output voltage of the circuit 2 increases, and as described above, the delay time of the minute variable delay circuit 27 is decreased, and the timing of the delay signal is controlled to match accurately.

Note that the limiter circuit in the phase control circuit is provided to prevent errors in the phase detector from occurring due to fluctuations in burst amplitude, and is not necessarily necessary.

It goes without saying that the present invention may be constructed with circuits that perform the same function other than those described using the specific circuit examples.

Effects of the Invention As described above, according to the present invention, since the amplitude and phase of the burst signal of the input signal of the 1H delay circuit and the delayed signal are compared and controlled, the delay time due to temperature change of the ultrasonic 1H delay line, etc. Fluctuations can be effectively compensated. Another advantage is that even if the 1H time and color signal level of the input signal deviate from normal, it can be followed.

In addition, since all of the comparison circuits for the amplitude and phase of the burst signals of the original signal and the delayed signal can have the same configuration using the same elements, the temperature characteristics of the control circuits themselves also work to compensate for each other, resulting in improved temperature stability. It also has the advantage of being extremely good.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the basic configuration of a general comb filter, Figure 2 is a frequency characteristic diagram of the comb filter, and Figure 3 is an example of the configuration of a comb filter using an ultrasonic delay line. 4 is a block diagram showing the configuration of a video signal processing device according to an embodiment of the present invention, FIG. 5 is a signal waveform diagram explaining its amplitude control operation, and FIG. 6 is an amplitude control diagram in the same device. A specific circuit diagram of the circuit, FIG. 7 is a vector diagram explaining the burst phase for phase control in the same device, FIG. 8 is a signal waveform diagram explaining the phase control operation in the same device, and FIG. 9 is a vector diagram explaining the burst phase for phase control in the same device. FIG. 2 is a specific circuit diagram of a phase control circuit in the device. 29, 30... Burst gate circuit, 31, 3
2...Amplitude detection circuit, 36...90° phase shift circuit, 3
9... Phase detection circuit, 23... 1H delay line, 25
...Variable gain control circuit, 27...Minute variable delay circuit.

Claims (1)

[Claims] 1 A 1H delay circuit that delays the television video signal by approximately one horizontal scanning period, a variable gain control circuit whose amplification degree is varied by an externally applied control voltage, and a delay time which is varied by an externally applied control voltage. A minute variable delay circuit is connected in series, and a burst is generated from the television video signal delayed by one horizontal scanning period by the 1H delay circuit and the minute variable delay circuit, and the television video signal before being delayed. Extract the signal 2
2 burst gate circuits and 2 burst gate circuits taken out above.
An amplitude comparison circuit that compares the amplitudes of two burst signals, generates a DC voltage according to the difference in amplitude, and supplies the DC voltage to the variable gain control circuit as the control voltage to control the amplitudes of the two burst signals to match. , a phase shift circuit that shifts the phase of one of the two burst signals by 90 degrees, and a phase shifter that compares the phases of the two burst signals and generates a DC voltage according to the phase difference. and a phase comparator circuit that supplies the control voltage to the minute variable delay circuit to control the phases of the two burst signals so that they are in a 90° relationship with each other.