JPS5897992A - Chroma signal recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To emphasize and recording a low-level signal through a chroma emphasis circuit during recording, and to eliminate non-linearity of recording through a chroma deephasis circuit during reproduction. CONSTITUTION:Only a chroma signal in a video signal inputted from an input terminal 1 is extracted through a BPF7. Then, the chroma signal adjusted to a specific level by the AGC circuit consisting of a variable gain amplifier 8 and a detecting circuit 12 is inputted to a chroma emphasis circuit 31. The chroma signal having a low-level signal emphasized is frequency-converted to a low frequency band by a recording processing circuit 10 and outputted as a low-frequency converted color signal through an LPF11. This signal is inputted to an input terminal 33 through a regenerative amplifier and supplied to an LPF24. The chroma signal passed through the LPF24 is adjusted to a specific level through the AGC circuit consisting of a variable gain amplifier 25 and a detecting circuit 29 and then reconverted from the low-frequency converted color signal into the original chroma signal through a regeneration processing circuit 26 and a comb-shaped filter 27. Then, a chroma deemphasis circuit 34 corrects nonlinearity of recording.

Description

[Detailed description of the invention] The present invention relates to a chroma code recording and playback method.

In particular, the present invention relates to a ROMA signal recording and reproducing circuit that is suitable for reducing noise mixed in low-level chroma signals.

FIG. 1 shows the configuration of a signal processing circuit of a conventional video tape recorder (hereinafter referred to as VTR).

First, let's talk about records. The signal input from the signal input terminal 1 is divided into a luminance signal and a chroma signal by i, p, p2 and B, P, F7.

The luminance signal is recorded and processed by a luminance signal recording processing circuit 3, a frequency modulation circuit 4, H, P, F 5, and is input to a mixing circuit 6. On the other hand, the chroma signal is processed by variable gain amplifier 8.
A, C, (,', (self.

The dynamic chroma signal control circuit sets the level so that the output signal level is always constant even if the input signal level fluctuates. Thereafter, the chroma signal converted into a low frequency conversion carrier color signal by the chroma signal recording processing circuits 9, 10 and P, F, 11 is input to the mixing circuit 6 and superimposed on the one-frequency modulated luminance signal. The recording video signal outputted from the mixing circuit 6 is amplified by a recording amplifier circuit 15 and recorded on a magnetic tape 15 via a video head 14. Furthermore, what is the chroma signal recording processing circuit 9.10?

For example, it is all or part of a frequency conversion circuit, a burst emphasis circuit, and a pseudo burst addition circuit.

Next, playback will be explained. The signal is reproduced from the magnetic tape 15 via the video head 16.

The regenerative amplifier circuit 17 amplifies the signals H, P, F', 1B, and so on.

It is divided into a luminance signal and a chroma signal by p, p, 24. The frequency-modulated luminance signal is demodulated into a luminance signal by the luminance signal reproduction processing circuits 19 and 21 and the demodulation circuit 20, and is input to the mixing circuit 23 through L, P, F, and 22. - 10,000, the low frequency conversion carrier chrominance signal passes through the A C"C circuit consisting of the variable gain amplifier 25 and the detection circuit 29, and then passes through the chroma signal reproduction processing circuits 26, 28 and the comb filter 2.
7, the low-pass conversion carrier color signal is converted into a chroma signal, and the signal is input to the mixing circuit 26. The luminance signal and the chroma signal are mixed in the mixing circuit 23 and outputted from the output holder 30 as a reproduced video g11 signal.

The luminance signal reproduction processing circuit 19 is, for example, a dropout canceller circuit or a limiter circuit, and the luminance signal reproduction processing circuit 21 is a luminance signal de-emphasis circuit. Generally, the limiter circuit needs to be in the circuit 19. Further, the chroma signal reproduction processing circuit 26 is a circuit including at least a frequency conversion circuit, and the chroma signal reproduction processing circuit 26 is a circuit that includes at least a frequency conversion circuit.
8□1 is, for example, burst de-emphasis times 916. These are a pseudo burst removal circuit and an HPF.

In a conventional VTR having the circuit configuration as described above, the characteristics of the comb filter provided on the reproduction side play an important role. In other words, the comb filter has a 1H delay line (1H delay line).
(H refers to the horizontal scanning period), but in reality, spurious signals are generated from the delay line and appear as disturbances on the screen, causing problems. Also, Teru WL
The FM signal and the low-frequency conversion carrier color signal have partially overlapping bands, and crosstalk to the low-frequency conversion carrier color signal due to the lower side band of the luminance FM signal causes cross color, which poses a problem. moreover.

The number of deviations of H from the adjacent track (hereinafter abbreviated as α1) is 1o
In the case of B or α75H, set it to the same level as B (the horizontal sync signal recording positions should be set to 5 so that they are adjacent to each other between adjacent tracks)
This causes a problem of burst signals leaking from adjacent tracks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a chroma signal recording and reproducing circuit for a video tape recorder which eliminates the drawbacks of the prior art and reduces noise mixed into the chroma signal.

In order to achieve the above object, the present invention includes an input terminal into which a chroma signal is input, an amplitude limiter that limits the amplitude of the chroma signal applied to the input terminal, and an amplitude limiter that limits the amplitude of the chroma signal and the amplitude limiter. A means for adding the output signal is provided, and by adding the output signal of the #amplitude limiter during recording, the black 1 signal is strengthened, and during playback, it is complemented with the recording system at the subsequent stage of the comb filter. The chroma S/N is improved by adjusting and reproducing the characteristics based on the relationship between the two.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. FIGS. 2 and 3 show the configuration of an O-ma signal recording and reproducing circuit according to the present invention. The difference from the conventional example shown in FIG. 1 is that a chroma 1m emphasis circuit 61 and a chroma de-emphasis circuit 34 are provided. In other words, during recording, a nonlinear circuit called a chroma emphasis circuit is used to amplify low-level signals for recording, and during playback, a chroma emphasis circuit that has a complementary relationship with the human power vs. output characteristics of the nonlinear circuit in the recording system is used. By providing a de-emphasis circuit, nonlinear characteristics during recording are removed and the original signal is restored.

In FIG. 2, only the chroma signal is extracted from 5 of the Eirin signals input from the input terminal 1, B, p, p, and 7. Thereafter, the chroma signal adjusted to a constant level by the A(,'C circuit) consisting of the variable gain amplifier 8 and the detection circuit 12 passes through the chroma signal recording processing circuit 9 and becomes the chroma signal.
The signal is input to the emphasis circuit 31. The chroma signal with the low level signal emphasized in the chroma emphasis circuit 31 is converted from low frequency to frequency in the primary chroma signal recording processing circuit 10, and passes through L, P, and F 11 to become a low frequency converted carrier color signal. The signal is output from the output terminal 52 to the mixing circuit with the luminance signal. The above is the chroma signal recording circuit according to the present invention.

FIG. S shows a chroma signal regeneration circuit according to the invention. The signal amplified by the reproduction amplifier is input to the input terminal 35. The chroma signal extracted by L, P, and F 24 is sent to an ACC circuit consisting of a variable gain amplifier 25 and a detection circuit w129.
The signal is adjusted to a constant level by the circuit, and is converted from the low-pass conversion carrier color signal to the original chroma signal by the chroma signal reproduction processing circuit 26 and the comb filter 27. after that,
When recording with the chroma de-emphasis circuit 64,
The chroma signal whose nonlinear characteristics have been corrected by the emphasis is outputted from the output terminal 35 to a mixing circuit with a luminance signal, after passing through the chroma signal reproduction processing circuit 28.

According to this embodiment, spurious interference (burst and pseudo-burst interference is large in %) generated from the delay line constituting the 11+<L-type filter, which has been a problem in the past, Cross color interference (such as leakage of burst signals or pseudo burst signals from adjacent tracks when 51B is not arranged) is suppressed, resulting in an improvement in chroma S/N.

The first feature of FIGS. 2 and 5 is that the chroma de-emphasis circuit 54 is provided after the comb filter 27. The reason for this is among the conventional problems (11 and (31)
This is to solve the problem. That is, regarding (11), since burst interference occurs at the output of the comb filter, the only way to suppress this is to provide a de-emphasis circuit wI54 on the output side of the comb filter 27.

(For '51 as well, the effect of the de-emphasis circuit 54 cannot be produced unless crosstalk from adjacent tracks is sufficiently suppressed by the comb-shaped filter 27. From this, the de-emphasis circuit 54 cannot produce the effect of the comb-shaped filter 27.
It is necessary to provide it on the output side of 7.

The second characteristic of FIGS. 2 and 5 is that the level of the human input signal (or output signal) of the chroma emphasis circuit 610 and the level of the output signal (or input signal) of the chroma de-emphasis circuit 34 are approximately equal to 11.5ACC The loop is made up of gold.

Chroma emphasis circuit 31. Both the chroma de-emphasis circuits 64 are non-linear circuits, and in order for the chroma de-emphasis circuits 64 to be inverse circuits, the input signal level of the emphasis circuit 51 and the output signal level of the de-emphasis circuit 54 need to be approximately equal.

Since the ACC circuit operates so that the input signal level of the detection circuits 12 and 29 is constant, it is arranged so that the input signal of the detection circuit 120 and the input signal of the emphasis circuit 51 are almost the same.

It is necessary to arrange the detection circuit 290 so that the human input signal and the output signal of the de-emphasis circuit 64 are approximately equal.

Alternatively, it is possible to arrange the input signal of the detection circuit 120 to be approximately the same as the output signal of the emphasis circuit 51. In this case, the arrangement may be such that the input signal of the detection circuit 290 is approximately the same as the input signal of the de-emphasis circuit 54.

In addition, in Figure 2, the detection roof of the ACC circuit is shown as 1. It was taken out from in front of the Kusema En7 assist circuit,
It can also be taken out after the Chroma En7 assist circuit. Similarly, the detection loop in FIG. 6 can be taken out before the chroma de-emphasis circuit.

Examples of the chroma emphasis circuit and chroma de-emphasis circuit are shown in FIGS. 4 and s. The chroma emphasis circuit shown in FIG. 4 divides the chroma signal input from the input terminal 36 into a thread path that passes through the limiter circuit 37 and a thread path that retains the original signal, and adds and mixes them in an adder circuit 58 and outputs the chroma signal to the output terminal. This is what is output from. The IJ input circuit 57 outputs a signal with limited amplitude in response to a large amplitude signal, and the characteristics of the Chroma En7 assist circuit shown in FIG. This limits high level signals. The chroma de-emphasis circuit shown in FIG. 5 is a version of the circuit shown in FIG. 4 which has negative feedback type reverse circuit characteristics. The reproduced chroma signal inputted from the input terminal 40 is subtracted by the subtraction circuit 41 from the output terminal 42 through the subtraction circuit 41, and is outputted to the output terminal 42. That is, the reproduced chroma signal is subtracted by the subtraction circuit 41 from the output terminal 42. circuit 5
If the transfer function of 7 is 1 (aIl), then the transfer function R(Φ) of the chroma emphasis circuit is given by the following equation.

R(IIJl = 1 + Hl(sl) Also, the transfer function P of the chroma de-emphasis circuit shown in FIG. 5 is as follows.

p (*l= 1/(1+f1(a+l)) Therefore, the transfer function By of the emphasis and de-emphasis circuits (if ml is equal, the transfer characteristic of the overall emphasis and de-emphasis is R(lightI1.P(#1=( 1+B1 moari/(1+81 (
(4111=1, and the nonlinear characteristics caused by the emphasis circuit are corrected by the de-emphasis circuit, and the original signal can be almost completely restored.

Another embodiment is shown in FIGS. 6 and 7. The difference from FIG. 4 and FIG. 5 is that a chroma signal sideband extraction circuit 43 having the characteristics shown in FIG. 8 is provided in the limiter circuit thread path. In other words.

Emphasis is applied only to the sideband of the chroma signal. The sideband of the chroma signal is a high frequency band with a low level and is susceptible to noise. Therefore, by performing sideband emphasis during recording and performing sideband de-emphasis during reproduction, the S/N ratio of the black 1 signal can be improved and a reproduced image of high quality can be obtained.

FIGS. 9 and 10 show a case where the chroma processing circuit of the present invention is used for both recording and reproduction. In FIG. 9, the recording/reproduction changeover switch 47 plays an overlapping role. First, recording will be explained. input.

Only the fifth chroma signal of the video signal is input to the terminal 44. During recording, the recording/reproduction switch 47 is in the position shown, and the variable gain amplifier 8 and the detection circuit j! 12 is a record A
Operates as a CC circuit. The chroma signal whose level has been adjusted by the ACC circuit passes through the chroma signal recording processing circuit 9 and is input to the chroma emphasis circuit 'A1, where the low level signal is emphasized. The chroma signal is further frequency-converted to a lower frequency band by the chroma signal recording processing circuit 10 and outputted to the output terminal 45. Next, reproduction will be explained.

Of the reproduced video signal, only the chroma signal is input to the input terminal 44 which is common to the recording. During reproduction, the recording/reproduction changeover switch 47 is switched to the opposite position from that shown, and the gain amplifier 8 and the detection circuit 12 operate as an ACC circuit for reproduction.

The chroma signal that has passed through the ACC circuit is converted by the chroma signal reproduction processing circuit 26 and the comb filter 27 from the low-pass conversion carrier color signal to the original chroma signal. Thereafter, in the chroma de-emphasis circuit 54, the chroma signal whose characteristics have been corrected by the encoder assist circuit during recording is passed through the chroma signal reproduction processing circuit 211 to the output terminal 4.
It is output from 6. By providing the recording/reproduction changeover switch 47 as described above, ACC regression for recording and reproduction can be made common use.

Figure 10 is an example in which the loop of the ACC detection circuit is different from that in Figure 9.
After the assist circuit 61, it is returned to the detection circuit 12.
In the case of playback, the signal is returned from before the chroma de-emphasis circuit.

Note that the above chroma emphasis and chroma de-emphasis are explained in terms of carrier color signals, but of course, emphasis and de-emphasis can also be applied to low-frequency conversion color signals.

It is also possible to perform an enfu 1 sis.

Also, the en7 assist may be just the chroma sideband en7 assist.

According to the present invention, it is possible to reduce the noise mixed in the chroma signal, thereby improving the chroma S/N of the reproduced image.

%K<Spurious interference from the delay line that makes up the L-type filter, cross-color interference from the 7FM signal, nost signal leakage from adjacent tracks, and Ar1
The effect of the present invention on chroma interference in the 60-bit signal for use is extremely significant.

Furthermore, according to the present invention, the recording emphasis circuit and the reproducing de-emphasis circuit can be easily reversed, resulting in extremely good restorability.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional signal processing circuit, FIG. 2 is a block diagram of chroma signal recording processing using the present invention, FIG. 5 is a block diagram of chroma signal reproduction processing using the present invention, and FIG. , Figure 5 shows a chroma emphasis circuit and a chroma de-emphasis circuit, Figures 6 and 7 show another emphasis circuit and de-emphasis circuit, and Figure 8 shows sideband emphasis characteristics. Figures 9 and 10 are A
FIG. 2 is a configuration diagram of the present invention in which a CC circuit is used in common for recording and reproduction. 8.25...Variable gain amplifier, 12.29...Detection circuit. Sl...Chroma-sha emphasis circuit W6.5a...Chroma-sha emphasis circuit, 27...Comb filter. 57...Limiter circuit, 58...Addition circuit, 41...
・Subtraction circuit. 43...Chroma signal sideband extraction circuit. 47... Recording/reproduction switching circuit. Representative Patent Attorney Susuki 1) Kosai Ri 2 Figure 3 Figure 4 Figure 1'5 Figure 6
Off figure O δ figure color rlJm, sending reed

Claims (1)

[Claims] In a device for recording and reproducing chroma signals, an input terminal to which a chroma signal is input manually, an amplitude limiter for limiting the amplitude of the chroma signal applied to the input terminal, and an addition of the #chroma signal and the output signal of the amplitude limiter. A chroma signal recording/reproducing circuit characterized in that it is provided with an adder that performs a chroma signal recording/reproducing circuit.