JPS5950681A - Frequency discriminator - Google Patents

Abstract

PURPOSE:To prevent a frequency discriminator from being malfunctioned because of discontinuous signals and dropout, by making a constant current source inoperative when a count value of a counter circuit is brought only once to a state at the outside of a prescribed range. CONSTITUTION:T-FFs 25, 26, 27, frequency-divide a horizontal synchronizing signal separated from a video signal by 1/m, where (m) is a positive integer. Further, a counter 24 is controlled with an output of a frequency division circuit and counts a pulse inputted at an nH period, where (n) is a positive integer. When the count value is more or less for a prescribed value than a reference numeral for >=2 consecutive values, the counter 24 drives a constant power supply 28 or 29 so as to output an output current of opposite polarity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency discriminator, and more particularly to a voltage-controlled keepsake oscillator (hereinafter referred to as VCO) that oscillates at a substantially constant frequency relationship with a horizontal synchronizing signal of a video signal reproduced from a magnetic recording device or the like.
This invention relates to a frequency discriminator suitable for controlling a frequency discriminator.

In a home VTR, the color signal is band-converted to the lower frequency side of the F'M-modulated luminance signal and recorded.This band-converted color signal is sometimes reproduced, as is well known.
It has time axis fluctuations.・For this reason, this time axis variation is caused in the carrier 1a signal for conversion to the original band, and the signal is reproduced.

A method to remove time axis fluctuations contained in color signals.

is being adopted. Home VTR.

Let's take a typical VH8 system VTR as an example.

1. Describes a specific method for removing time axis fluctuations. .

Ru0 Records and plays back NTSC television signals.

If the carrier frequency is IiOfH (h'horizontal scanning period.

The frequency is converted so that it becomes (wave number). at the same time.

The phase is shifted by 1° by 90° every 1H (H: horizontal scanning period), and the direction of this phase shift is as follows.

There are those that move in the backward direction and those that move in the forward direction.

It is possible to switch alternately for each field.

The signal is processed so that In this way low.

The color signal converted into a frequency is hereinafter referred to as a low frequency converted color signal. This low-pass conversion color signal can also be regenerated.

Color subcarrier frequency fB□ (= 3.579515
In order to restore the color signal of FJ(z), a color signal processing circuit having a configuration as shown in FIG. 1 is used. 1 was played.

The first part receives a low frequency converted color signal including time axis fluctuations.
Input terminal 2 is equipped with a video head.

The head pulse is synchronized with the rotation of the cylinder.

A second input terminal, 3, inputs a horizontal synchronizing pulse that is separated from the reproduced luminance signal and includes approximately the same time axis fluctuation as the reproduced low-frequency conversion color signal, 10, a third input terminal, 4. is the reproduced low-pass conversion color.

A first multiplication circuit for frequency converting a signal into a color signal of the original frequency; 5 is for the first multiplication circuit;

In order to extract a color signal of carrier frequency f80 from the power.

The first BPF, 6, is a burst gate for extracting 1) burst components from the first BPF output.

circuit, 7 is a phase comparator circuit, and 8 oscillates with fso.

An oscillator, 9 a frequency discriminator, and 10 a phase comparison circuit.

7 and the output of frequency discriminator 9.

Arithmetic circuit, 11c, center frequency 160fH toner 6V
C2,.

For 0, divide the output of VCOll by 1 and add 90'.

A 1' frequency divider circuit outputs a four-phase 11QfH signal with a phase shift, and 13 is a horizontal synchronizing pulse and a herad pulse.

The /In fH signal of the phase is switched and output every 1H, and there is a 90' phase delay for each H and a 90' phase delay for each H of 5.
Switching circuit that realizes 0° phase advance, 11 is switching circuit 1
A second multiplication circuit 15 multiplies the output of the oscillator output 8 by the output of the oscillator output 8;

From the output, the phase shifts by 90° for each H (fsa・
II for extracting a continuous signal of + tOfH) frequency
It is II2O3PF.

The carrier/transmission frequency of the color signal inputted from the first input terminal 1 is IQ fH + Δf (Δf is the frequency variation caused by the time axis variation). On the other hand, in the second multiplier 17I, the output of the oscillator 8 and the output of the switching circuit 13 are multiplied. If the Vooll frequency is 160° fH, the output of the switching circuit 11 is .

Since the frequency is aOfH, the output of the second multiplication circuit 13° is (fso + aofH) and (rso −7
1ofH).

Two frequency components are obtained. Second BP,...)
F15 extracts the (fsa + dofH) component. Since this (fso + aofH) component and the color signal are multiplied by the first multiplication circuit 4, the carrier frequency becomes (f
There are two colors: sa-'△f) and (fso +2AOfH+△f).

I get a signal. In the first BPF5, fs
. −Δf) is extracted. This (fso-.

Since the Δf) frequency is the frequency of the burst signal, the phase is compared with the oscillator 8 in the phase comparator circuit 7. Since there is a frequency difference of -Δf, a comparison output is output according to this frequency difference. . VCOll is controlled by this comparison amount 10 force, and finally the frequency of VColl becomes 1sofH+ a
△f, and the output of the switching circuit 13 is dofH+△f
Then, a signal having the same fluctuation as the time axis fluctuation of the input color signal can be obtained. At this time, the carrier frequency of the output of the first BPF s becomes exactly the same frequency as the output of the IR oscillator 8.

Stable color signals with axis fluctuations removed can be reproduced.

Here, however, the frequency discriminator is not working.

Until the frequency of vCOll reaches around 160fH.

It will work. That is, this V CO,...
.

No. 11 has sufficiently high control sensitivity and variable frequency range.

If it is not wide enough, it will not be able to absorb time axis fluctuations sufficiently, resulting in color and unevenness. It is normal to set the frequency variable width to 5% or more. On the other hand, as is well known, the burst (signal) is inserted for a period of about 3 μs every 1H, and has a spectrum every f with fso as the center. There is a stable point in the system in Figure 1, gifH.Here, if VCOll is (160fH-af
H) If it oscillates at a frequency (more than 2% low/high frequency),
The carrier frequency at the output of the first BPF5+n is (fso
−fH)−△f.

Of this, -61 minutes is absorbed, and finally,
The system becomes stable at a frequency of (fso - full). In this way, the circumference of VColl.

If the wave number is not within (ISO of H ± 2 fu), the color signal will be reproduced at an incorrect frequency.

It becomes.

Therefore, the frequency discriminator 9 selects the frequency of VC011.

is constantly measured, and the phase comparator circuit 7 always measures the correct frequency.

Therefore, it is necessary to control VColl within a range that allows the wave number to be controlled.

This frequency discriminator is usually constituted by a digimole circuit, and is specifically realized, for example, in the form shown in FIG. 17 is a fourth input terminal to which the output of VCOll is input; 18 is a fifth input terminal to which horizontal synchronization pulses are input;
19-23 are ant gates, 24 is a counting circuit, 25.
26.27 is a T-F, F, , 2B, .29 constant current source circuit. 25-27 T -F, F, ・Q
When the output is high, that is, 4V in Figure 3) from In to (
During the second instar, AND gate 19 is VCOll.

It operates so as to input the output to the counting circuit 2d.

In the counting circuit 24, the Q outputs of T-F, F, and 27 are high.

During the 1H period immediately before the change (period shown in Figure 3 (1v)), a.

A reset is applied by the output of the second gate 23. The 1° counting circuit 24 counts the output of VC011 during the 7fH period.

Works like a number. If the count value of the counting circuit 27I is 160 X A + 4 or more (that is, the frequency of VColl is 161fH or more), the AND gate 20
The output input to becomes high, and the output is 16o x 4-4 or less (
That is, if the frequency of ■C011 is below 159°fH), it is input to the AND gate 21.

output goes high. As is clear from Figure 3, this state remains until the next reset (xtl).
In other words, the period (lx), (x)·(x1)) continues.

The other input of each of the AND gates 20 and 21 is controlled by the AND gate 22, and becomes high for 1H period (X) of this output state.
If the frequency 10 of the VCOll is 161 fH or more during the period of , then the output of the AND gate 20 is ・159 fH or less, the output of the AND gate 21 is .

Each gets high.

The constant current source 28 is a VCO only when the input is high.

A current is output with a polarity that changes the voltage in the direction in which the frequency of 11 decreases, and the constant current source 29 is at high input.

Configured to output a current of opposite polarity.

It will be done.

In the following manner, every 8H, 1H period.

-17 when the 760110 frequency is higher than the predetermined frequency
It outputs an output so as to change the frequency of vColl when it is low or low.

The frequency of VCOll is between 159fH and 161fH.

Sometimes, the correct frequency is determined by the operation of the phase comparator circuit 7.

Since vColl is controlled to match the wave number, there is no need for the frequency discriminator to output an output.

This frequency discriminator 9 is a digital one as described above.

It is essentially a very positive circuit.

Although accurate frequency discrimination is possible, in reality, 1'□ has two drawbacks as explained below.

There is a strong desire to improve the performance of

The first is at the top of the screen, where the hue sometimes becomes large.

One of the causes of so-called color flicker.

The second reason is that it is one of the factors that increases the hue change at the time of dropout.

These two causes are the same. If the period of the horizontal synchronizing signal input to this frequency discrimination circuit is disturbed, the counting time of the counting circuit 24 changes. It is created in order to operate in a stable manner.

At home v'ra, two heads are used and one frame is used.

The head is switched and used for each yield.

Therefore, the signal becomes discontinuous at the switching section of the head.

In this part, the period of the horizontal synchronizing pulse does not become IH correctly and changes by about ±0.2H at most. Therefore, this discontinuous part falls within the interval from (V) to (vllll)' in Figure 6. Then, the period during which the AND gate 19 is open is not correctly 71H. Therefore, even if the frequency of 1 VCOll is correctly 16[1fH], the counting period is not 71H, so the number of counting pulses is 16[fH].
The number differs from ×a by the error of that period. For example, if the period of the horizontal synchronizing pulse becomes 1.2H at the discontinuous part,
The counting period is 4.2 hours.

Become. Therefore, the number of counting pulses is 160 x 4.2
””.

The number becomes 672, which is an increase of 32 pieces. Therefore, Zhou.

It is determined that the wave number is too high, and the constant current source 28 is operated.

■ Operate in the direction of lowering the frequency of C011.

Ru. ,,1
This discontinuity occurs about 6H before the vertical synchronization pulse, so if it takes time to absorb the frequency disturbance caused by this, it will affect the upper part of the screen.

At the time of dropout, a false horizontal synchronization pulse is generated due to noise, so that the total number of ticks may not be 4H, which also causes frequency and wave number disturbances.

An object of the present invention is to provide a (1) one-frequency discrimination device that does not cause color flicker and reduces hue inconsistencies during dropouts.

In other words, signal discontinuity due to head switching.

Frequency discriminator caused by dropouts.

The malfunction of is a one-off occurrence, and the output of the frequency discriminator due to the frequency deviation of vCOo is 1-.

It must be output continuously for a period longer than that specified.

The output from the counting circuit is repeated two or more times in a row.

Operate the constant current source only when a signal is generated.

Frequency discrimination by discontinuities and dropouts.

This prevents the device from malfunctioning. '2. .

An embodiment of the present invention will be explained below with reference to FIG.

do. In FIG. 4, 31 is an OR gate, and 32 is an OR gate.

NAND game), 53.38*A5 is AND gate,
.

35+3S, 37,39*'0,41.112 is inverter, 3/1 is D゛-F, Fl, At is RS F'
,F. At 5 in FIG. 3, VCOll is correctly oscillating at 16ofH.

In this case, after the counting circuit is reset, ・637
The output on the side input to the AND gate 21 is in a high state until counting 4 input pulses, then 4 pulses are counted, and when exactly 640 pulses have been counted, the 10 count stops. Therefore, the output of OR gate 31 is as shown in Fig. 5 (
i). When the outputs of the OR gate 31 and the AND gate 22 are NANDed, the output remains low as shown in FIG. 5U). Therefore, D−F, F,
Since the output of 1) remains low, the AND gate output also remains low.

Ku. Therefore, the Q output of R8F, F, is also p-like.

The state continues, and the output of the AND gate 53 also becomes low.

Next, the period from (v) to (will) is AH tena
l),.

Consider a case where the count value becomes 636 or less. AN2. .

, 11° The counting operation of the counting circuit 24 of the D gate 19 is completed.

When the output goes wide, the output input to the AND gate 21 remains high, so the output of the OR gate 31.

As shown in FIG. 5 (i/), the high state continues from the interval (1v). Therefore, the output of the NAND gate 32 is A5N
Only during the period when the output of the D gate 22 is high, it becomes low as shown by (j/). This pulse is D −F, ・F,
After being delayed by 1H, the rising part of the pulse passes through a circuit (consisting of inverters 55, 36, 37, and an AND gate) that differentiates and divides the pulse.
pulse between (XI) and <xl) as shown in k').

is input. Therefore, after (Xl+) RSF,
F.

Output goes high. However, the AND gate 22.

The output is high only in the father's room, so AN.

The output of the D gate 33 still remains in the 4-state.

Therefore, AND gate 21 is still high.

There's nothing to do. Similarly, the interval from (V) to (vl) is aH.

In this case, the count becomes longer than 6t4 and counting stops.

think. At this time, the output of the OR gate 31 is as shown in FIG.

, 12° output is like (j″), and again, RS lli
A pulse of (k') is applied to the human power of ', F, -34, and (xii)・After that, the output of RS F, F, 34 is (e'
) to get high. However, at this time as well, it becomes high only when the output of AND game 22 is held, so the AND
The output of gate 355 remains low.

In this way, until then, the counting time is normal and the VCO is
The frequency of ll is also set correctly to 160fH, but if the count suddenly changes and goes out of the specified range, check the VCO.
The constant current source that controls ll does not operate at all. next,
In the previous state, the count value was 636 or less.

Or it is 6AA or higher and continues to be counted.

Consider the case where the value is 636 or 664 or more.In this case, the AND gate 22 becomes high.

Section R8F, F is in a high state, so A.

The output of ND Agate 3 is shown in the section (m''').

Get high on sea urchins. Therefore, this (2) interval total.

The constant current source operates on the high side of the output of several circuits 2t.

You will be forced to do so. After this, the output of 22 is set. .

Circuit for differentiating the downstream (inverters 59.10, 41.(
RS F, F',
A reset pulse is manually applied between (X) and (XD) as shown in (h).
FJ', mouth.

-, but from the AND gate 38, (XI) and (x
ll).

During this period, the set pulse is manually applied again, so R8S F
, F, aa's output is (1') and C as shown in .

Returning to step A, calculate the current due to the next output of the counting circuit 2t.

The state is such that source control operation is performed.

In this way, the frequency is outside the predetermined range.

However, the count value of the counting circuit 24 is outside the predetermined range.

If things happen one after another, it is the same every time from the second time onwards.

This will operate the current source.

As explained above, the counting circuit 2d only - times.

Since the constant current source does not operate when the count value is outside a predetermined value, this frequency discriminator does not malfunction due to signal discontinuity or dropout.

For purposes of explanation, this frequency discriminator is used in a VH8 system VTR that handles NTSC system television signals. ! Although explained in case 9.-, it is clear that the present invention can be used to handle television signals of other systems or to VTRs of other recording systems by simply changing the value of the counting circuit as appropriate. It is also clear that regardless of the color signal processing circuit, the present invention can be similarly used when controlling a VCO, motor, etc. so as to have a predetermined relationship with the horizontal synchronizing pulse. Also, video
It goes without saying that it can also be used for video signal reproducing devices other than VTRs, such as discs. - As explained above, according to the present invention, the C frequency discrimination operation malfunctions due to the counting period and set membrane error due to discontinuity of the signal 10, dropout error, etc.

This prevents color flickering and deterioration.

Hue disturbance when drop-out occurs can be reduced, and performance and performance can be significantly improved. 1)

[Brief explanation of drawings]

Figure 1 shows the color signal processing circuit of a home VTR. A block diagram showing an example, FIG. 2 is the frequency of FIG. 1. FIG. 3 is a block diagram showing a conventional example of a discriminator. A diagram showing the timing chart of each part in Figure 2, 2°, 1
5. FIG. 6 is a block diagram showing an example of a frequency discriminator according to the present invention, and FIG. 5 shows the timing of each part of FIG. 4. FIG. 2t...Counting circuit, 28.29...Current source,
25.26.27...'I'-F', F',,34
...D -F,F,, -44...R8F,F
,. Representative Patent Attorney Susuki +J3 i,! :ge', 4.1
6.

Claims (1)

[Claims] The horizontal synchronizing signal separated from the video signal is divided by 1° (m
is a positive integer), the -frequency divider circuit and the -divider εm
Controlled by the output of the m-circuit circuit,
A pulse input during a period of nH (n is a positive integer, H is one period of the horizontal synchronization signal). A counting circuit that measures the number of steps, and a counting circuit that measures the number of steps. When the number of pulses in the nH period is -1 or less for a number of consecutive times (a is an integer of 2 or more) or less, and +1 for a number of consecutive pulses for a number of times or more. of opposite polarity when: output current until the next counting operation is performed. A current source circuit that is controlled to output for a certain period of time. A frequency discrimination device comprising: .