JPS59219089A - Color process circuit of magnetic recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To prevent flicker from being produced on the upper part of a screen by quickening the response speed of a filter means controlling a voltage controlled oscillator through the utilization of a head output switching signal. CONSTITUTION:A switch circuit 19, an input terminal 20 and a commandsignal generating circuit 21 are added to a detection filter 8. When a head output switching signal is supplied to the input terminal 20, the command signal generating circuit 21 generates a command signal having a prescribed pulse width after a pescribed period is elapsed from each edge of a switching signal, and supplies the signal to the switch circuit 19. Then a pulse width period moving contact 19a of the switch circuit 19 is connected to the contact A to open the filter 8. Thus, the correcting output of a frequency fluctuating component from a phase detector is transmitted directly to a VOC9. Then the response speed of the APC loop is quickened and the production of flicker on the upper part of the screen is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color process circuit for a magnetic recording/reproducing circuit such as a video tape recorder.

[Background of the invention]

Hereinafter, a color process circuit of a conventional video recorder (hereinafter abbreviated as VTR) will be explained with reference to the drawings. FIG. 1 is a block diagram showing an example of a conventional VT)L color process circuit.

In the figure, 1 is an input terminal for a reproduced color signal (reproduced low-pass color signal) that has been low-pass converted, and 2 is a first frequency converter (hereinafter referred to as
3 is the first band pass filter (hereinafter abbreviated as 10BPF), 4 is the output end of the reproduced color signal converted back to the original carrier frequency (3.58MHz), 5 is the burst A signal extraction circuit, 6 is a phase detector, 7 is an X-tal oscillator that oscillates at the color image carrier frequency fcc, 8 is a detection filter, and 9 is a voltage controlled oscillator using X-tal (hereinafter referred to as X-talVco). ), 10 is the second converter, 11 is the 20th BPF 112 is the input terminal of the reproduction horizontal synchronizing pulse, and 13 is the AF C (Automa
tic Frequency Control) /
14 is a phase shift circuit.

In FIG. 1, if the reproduced low-range color signal applied to the input end 1 does not contain a frequency fluctuation component or a time axis fluctuation component, the signal is frequency-converted by a first converter 2 and converted into a first converter. As a result of extracting the original color signal components by the BPF 3, a reproduced color signal converted to a predetermined frequency is outputted from the output terminal 4.

However, the reproduced low-range color signal contains frequency fluctuation components caused by tape stretching, instability of the running system, and the like.

For this purpose, in FIG. 1, blocks 5 to 14 are provided, and a correction component of the frequency fluctuation component is added to the frequency conversion carrier wave input to the first converter 2, and the frequency fluctuation component is added to the frequency conversion carrier wave input to the first converter 2. We are trying to remove the ingredients.

The burst extraction circuit 5 extracts a color burst signal from the reproduced color signal which is the output of the first BPF 3, and supplies it to the phase transverse transducer 6. Phase detector 6
Then, the color burst signal and the output of the X-ta1 oscillator 7 are compared in phase, and a phase error correction signal is output.

This phase error correction signal of the phase detector 60 is smoothed by the detection filter 8 and supplied to the X-tal Vco 9 as a control signal. As a result, X-talVc09 oscillates near fsc in response to the control signal.

Next; the output signal of the -X-tal VCO 9 is output to the second converter 10. For this reason, in this second converter 10, if the blocks 12 to 14 are not considered, the carrier wave for frequency conversion, which reduces the correction component of the frequency f dynamic component, is passed through the second BPFll. , output to the first converter 2. That is, in the blocks 5 to 9 constituting the APC loop, as mentioned above, the output signal of the X-tal VCO 9 is adjusted to
llJ is in control. For this reason, the second converter 1O can be moved to correct the frequency variation component referred to in the color burst signal when it is present.

However, the correction ability of the A)'C loop is only 2/2fH (fH is the horizontal synchronizing signal frequency) with respect to the color law carrier frequency fsc, and furthermore, the stable point of the reproduced color signal is:
fF4c r, exists every 2nfH (n is an integer) with 32 centers. For this reason, the APC loop alone may not be able to keep up with the frequency order 1 encirclement, or may be locked incorrectly.

Therefore, in FIG. 1, the reproduced horizontal synchronizing pulse is
The AFC loop 1 section 13, which operates the VCO 7d', multiplies the reproduced low-range color signal or a frequency close to += of the reproduced low-range color signal. Thereafter, the phase shift circuit 14 carries out a phase shift to restore the phase shift made to the color signal during recording, and the color signal is supplied to the converter 10 of the culvert 2. Therefore, the phase shift circuit 14 outputs a signal containing the frequency fluctuation component included in the reproduced horizontal synchronization signal.

Next, in this second converter 10, the above-mentioned X-t
The output signal of the alVco 9 and the output signal of the phase shift circuit 14 are multiplied and this (W) is supplied to the 20th BPF II. As a result, the first converter 2 receives the frequency fluctuation component of the two output signals. A carrier wave for frequency conversion to which a correction component of As a result, a reproduced color signal whose center band is fsc from which the frequency fluctuation component has been removed is obtained at the output end 4. That is, it is possible to reproduce a correct color signal.

However, in the correction of the frequency fluctuation component using the above method, if the frequency of the reproduced low gamut color Ig changes suddenly, the AFC including A, the PC loop and the phase shift circuit 14
The loop response could not be followed, which caused flicker (colored unevenness) at the top of the screen, which was unsightly. In addition, in the case where the frequency of the reproduced low-range color signal changes suddenly, especially at the point in time (switching point) when the signal read out from the track pattern recorded on the tape using, for example, two heads, is switched. There is a timing difference, etc.

FIG. 2 is a block diagram showing another example of a conventional VTR color processing circuit. In the figure, the same as in Figure 1 -
Parts and equivalent parts are indicated by the same reference numerals.

15 is a VCo that oscillates at a frequency that is 160 times the horizontal synchronizing signal frequency fy or close to that value; 16 is a frequency discriminator; 17 is an adder; and 18 is a detection filter.

In FIG. 2, the frequency discriminator 16 divides the output of C015 - Ei by 160, and compares this frequency-divided signal with the reproduced horizontal synchronization signal from the input terminal 12 to obtain a frequency fluctuation component. A signal for correcting (error control signal) is supplied to the adder 17.

On the other hand, the APC loop consisting of blocks 5 to 7, especially the phase detector 6, also supplies a signal for correcting the phase error of the reproduced color signal to the adder 17.

The adder 17 outputs a signal obtained by adding the phase error correction signal and the error control signal to the detection filter 18. The inertia filter 18 smoothes the added signal and supplies it to the VCO 15 as a tBIJ control signal. Therefore, the VCO 15 oscillates near 16 (lfH) in response to the control signal, but this signal is divided by Δ (not shown) immediately before being input to the phase shift circuit 14.
and is supplied to the phase shift circuit 14.

This signal processing in the phase shift circuit 14 and the second converter 10. 20th BPF II, 1st converter 2, 1st
Since the signal processing in the BPF 3 is the same as that described in FIG. 1, it will be omitted here. Note that, unlike the case in FIG. 1, the output of the X-ta1 oscillator 7 is supplied as one input of the second converter 10.

That is, in the conventional example shown in FIG. 2, the correction components of the two frequency fluctuation components are added together, so that only one vc015 is used to correct the entire frequency f dynamic component.

For this reason, in the circuit shown in Figure 2, compared to the circuit shown in Figure 1, there is no difference in response speed to fluctuations, and since it is a one-way correction, the response speed of the thread is faster, and paternal ringing etc. It has the advantage of being less likely to occur.

However, as explained in Fig. 1, the circuit shown in Fig. 2 also has the disadvantage that it is not possible to completely eliminate flicker at the top of the screen at the time of switching the signal g+ read out by the two heads, making it unsightly. Ta.

In addition, in order to eliminate the drawbacks of the conventional circuits shown in Figures 1 and 2 mentioned above, by increasing the response speed of the system so that it can respond to sudden frequency fluctuation components, it is possible to respond even to small fluctuation components. As a result, a problem arose in that the screen became unstable and the S/N ratio deteriorated.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color process circuit for a magnetic recording/reproducing circuit which eliminates the above-mentioned drawbacks of the prior art and does not cause flickering at the top of the screen and does not cause deterioration of S/N.

[Summary of the invention]

A feature of the present invention is that in a color process circuit of a magnetic recording/reproducing circuit that converts a reproduced color signal subjected to low frequency conversion into a reproduced color signal of a predetermined frequency based on at least an output signal of a voltage controlled oscillator, the voltage controlled oscillator The response speed of the filter means for supplying a component for correcting the frequency fluctuation component of the reproduced color signal subjected to the low frequency conversion is accelerated to a predetermined value by using the head output direction switching signal.

[Embodiments of the invention]

Hereinafter, the present invention will be explained using the drawings.

FIG. 3 shows a switch circuit 1 in addition to the detection filter 8 in FIG.
9 is a circuit diagram showing an embodiment of the present invention in which an input terminal 20 and a command signal generator 21 are added.

In this figure, the same reference numerals as in FIG. 1 indicate the same parts nr and υ.

When a head output switching signal as shown in FIG. As a result, as shown in FIG. 5(b), from the HPF 31
H' synchronized with the etching of the switching signal (a) as shown in 4C.
Rus occurs.

The conopulse (b) is rectified by the double-wave rectifier 32, as shown in FIG. 5(C), and then supplied to the monomulti 33. In this monomulti 33, a pulse signal having a width corresponding to the 11H period is generated as shown in FIG. and supplies it to HPF34. HPF
34, a pulse signal (d) is applied to the strain shown in FIG. 5(e).
A pulse synchronized with the etching is generated and supplied to the monomulti 35 which is triggered by a negative pulse. This mono multi 35
In this embodiment, as shown in FIG. 5(f), a pulse signal having a width corresponding to a period of 8 to 12H is generated by a signal from a time constant circuit (not shown) inputted to the terminal 35a. , this pulse signal (f) is supplied to the switch circuit 19 (FIG. 3) as a command signal to the command signal generator 210.

In this switch circuit 19, A4 is in the ON state, and the B terminal is connected to the base rs potential 0, and the command signal if)
During the pulse width period, the movable contact 19a connects to the A terminal, and the detection filter 8 is brought into a zone state.

Therefore, in this state, the corrected output of the frequency fluctuation component from the phase detector 6 passes through the charge/discharge loop of the charge in the detection filter 8 and is directly transmitted to the X-tffilVcO9. As a result, the response speed of the APC loop is increased, and there is no delay with respect to the frequency fluctuation component at the switching point of the video signal, and 11! ] The flicker phenomenon at the top of the first page S no longer occurs.

In addition, in this embodiment, the pulse of the command signal (R) is not input to the switch (B) path 19 other than the pulse width period of the command signal "t(f), especially during the period of the first stray signal Jvj,
For this reason, the movable contact 19a is connected to the B terminal of the reference voltage VOg. As a result, since the output of the phase detector 6 passes through the charging/discharging loop of the detection filter 8 and is input to X-talVc (J9), no S/N deterioration occurs during the video signal period.

In addition, in the above-mentioned view, the generation of the command signal (f) is delayed by the width of the pulse signal (d), that is, the period of 11) (period) from the edge of the switching signal (a), due to the NTSC television signal. Then, in the vertical blanking period, no color burst signal, which is the reference of the color subcarrier, is inserted in the vertical synchronization pulse 3H period and the equalization pulse 3H period before and after it, which is a total of 9H periods. Therefore, the phase error correction component is not included in the output of the phase detector 6 during this 9H period, and in normal cases, the switching point of the two heads is the beginning of the vertical blanking period. More 2H
This is because it is on the upper side.

That is, the command signal (f) starts after the IIH period (2H plus 9H) from the switching point to the period during which the color burst signal exists during the vertical blanking period (8 to 12
The signal has a pulse width of a period corresponding to the H period).

Further, in this embodiment, the reference potential connected to BJ6 of the switch circuit 19 is set to a certain potential VO, or it goes without saying that it may be the ground potential (Ov).

Next, the switch circuit 1 is added to the detection filter 18 in FIG.
9. Another implementation pH/2 of the present invention with addition of an input terminal 20 and a command signal generator 21 is shown in FIG. 6 and will be described. In addition, in this figure, the same reference numerals as in FIG. 2 indicate the same parts and equivalent parts. Further, the specific circuit of the command signal generator 21 and its input/output signals are the same as those shown in FIGS. 4 and 5. 6, when the head output switching signal Yu3 as shown in section 51 (a) is applied to the input terminal 20, the command signal generator 21 outputs the same signal as described in the embodiment of FIG. Then, the command signal shown in FIG. 5(f) is output.

Therefore, the switch circuit 19 that receives the command signal (jl or human power) switches its movable contact 19a from the grounded B end to the A end during the command signal pulse period. 8 is in the oven state only during the pulse period of the command signal (f), so that the same effect as in FIG. 3 can be obtained.

That is, in this embodiment as well, the flicker phenomenon at the top of the playback screen can be significantly reduced.

In the embodiment of FIG. 3 of the present invention, the detection filter 8 is composed of capacitors CI, C2 and a resistance ratio of 1, and in the embodiment of FIG. 4, the detection filter 18 is composed of capacitors C3 to C5 and A resistor composed of resistor R3 was used. However, the detection filter used in the present invention is not limited to the above-mentioned filter, and any lag-lead type filter, for example, may be used.

Furthermore, even if the detection filter of the present invention is configured in multiple stages, and a predetermined filter group is connected to the switch circuit, and the remaining filter groups are connected only to the reference potential, the same effect as shown in FIGS. 3 and 6 can be obtained. It is easy to understand that the same effect as explained above can be obtained.

In the above explanation, the output f of the phase detector 6 or adder 17
Whether the X-tal is supplied to VCO9 or VCO15 via a detection filter or not, the detection filter is composed of, for example, a pair of filters with different time constants, and the time constant is changed according to the command signal (f). It is clear that the same effect as described above can be obtained even by switching from a filter with a large constant to a filter with a small time constant.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the command signal is supplied to the switch circuit that switches the time constant of the detection filter based on the head output switching signal. As a result of being able to speed up the response speed of the system that corrects frequency fluctuation components during the pulse period, flicker #4 at the top of the playback screen. In addition to preventing the occurrence of
It also has the effect of preventing deterioration of

Therefore, according to the present invention, it is possible to obtain a screen that is extremely easy to view and stable.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a color process circuit of a conventional VTI (Fig. 2 is a block diagram showing another example), Fig. 3 is a detection filter shown in Fig. 1, a switch l!l! circuit, and an input. FIG. 4 is a block diagram showing a specific example of the command signal generator, and FIG. 5 shows the input/output shown in the valley of FIG. 4. Waveform diagram (time chart) showing an example of the signal, Figure 6 is the second
FIG. 7 is a circuit diagram showing another embodiment of the present invention in which a switch circuit, an input terminal, and a command signal generator are added to the detection filter shown in the figure. 6... Phase detector 8, 18... Detection filter 9-X -tal VCO15/V C016... Frequency discriminator 17... Adder 19... Switch circuit 2o... Input end 21...・Command signal generator

Claims (1)

[Scope of claims] an input terminal for inputting a switching signal; a command signal generator for generating a command signal having a predetermined pulse width after a predetermined period has elapsed from the valley edge of the head output switching signal; and a command signal generator for generating a command signal having a predetermined pulse width; and a switching means for accelerating the response speed of the filtering means to a predetermined value by a pulse width period of the command signal. (2) A color process circuit of a magnetic recording/reproducing circuit characterized by: (2) A response speed of the filter means is accelerated to the predetermined value by controlling a charging/discharging time constant of the filter means. A color process circuit for a magnetic recording/reproducing circuit according to scope 1.