JPH04347993A - Chroma sub-nyquist sampling circuit - Google Patents

Abstract

PURPOSE:To insert a sub-Nyquist identification signal into the voice signal of a magnetic tape through the sub-Nyquist sampling recording of a chroma signal so as to expand the recording band of the chroma signal. CONSTITUTION:A recording sub-Nyquist circuit 20 sub-Nyquist sampling the chroma signal is provided in the recording system of a VTR, and an identification signal V with the same frequency as a horizontal synchronizing signal is generated by a luminance signal and recorded with an audio signal. In the reproducing system, a reproducing system re-sub-Nyquist circuit 25 sampling the reproduction chroma signal with the same clock is provided. When an identification signal is detected by an identification signal detection circuit 27, a changeover means 25 selects the sub-Nyquist sampling output and outputs the reproduction chroma signal as it is when the identification signal is not detected. Thus, even the chroma signal recorded by the conventional system can be reproduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma sub-Nyquist sampling circuit for expanding the band of chroma signals in a magnetic recording/reproducing apparatus.

0002

[Background Art] In recent years, television receivers (hereinafter referred to as TVs) have been getting larger screens and higher image quality, and magnetic recording and reproducing devices (hereinafter referred to as VTRs) have also been required to have higher image quality. ing. The band of chroma signals in conventional VTRs is, for example, approximately 350 KHz, which is not sufficient for larger screens and higher image quality of TVs. Therefore, efforts are currently being made to increase the band of chroma signals recorded and reproduced on magnetic tape and to widen the band of chroma signals input and output between TVs and VTRs, thereby improving image quality.

0003

[Problem to be Solved by the Invention] The chroma sub-Nyquist sampling circuit enables chroma signal output to be recorded and reproduced on a magnetic tape over a substantially wide band without expanding the occupied band of the chroma signal during recording and reproduction of a VTR. This is a circuit that performs band conversion processing. FIG. 6 is a block diagram showing an example of a chroma sub-Nyquist sampling circuit, in which (a) shows a recording system chroma signal sampling circuit and (b) a reproduction system chroma signal sampling circuit. Among video signals from a tuner section (not shown), a chroma signal C1 having a center frequency of 3.58 MHz is supplied to a decoding circuit 1 and converted into color difference signals RY and BY. These color difference signals are given to a low pass filter (hereinafter referred to as LPF) 2 and converted into chroma signals of low frequency components. The output terminal of the LPF 2 is connected to the vertical correlation detection circuit 3, the sub-Nyquist sampling section 4, and one terminal 5b of the changeover switch 5. The vertical correlation detection circuit 3 detects whether or not there is a correlation between chroma signals of adjacent horizontal scanning lines. The sub-Nyquist sampling section 4 is a circuit that samples the chroma signal of each horizontal scanning line using a 13.5 MHz clock, and further decimates the sampled signal to 1/16 to extract the chroma signal. Here, the chroma signals of adjacent scanning lines are sampled in a checkered pattern as described later, and applied to the terminal 5a of the changeover switch 5. When the chroma signals of adjacent horizontal scanning lines have a high correlation, the changeover switch 5 switches the common terminal 5c to the terminal 5.
If the correlation is low, the terminal is switched to terminal 5b.

FIG. 7 is a diagram showing frequency spectra of signals in each block of the chroma signal sampling circuit of the recording system and the reproduction system. As shown in FIG. 7A, the chroma signal output from the decoding circuit 1 is a signal having a band from DC to an upper limit frequency fc, and has a continuous spectrum. This chroma signal is converted to 13.5MHz/16 (approximately 843KHz) by the sub-Nyquist sampling section 4.
) is sampled at the sampling frequency fs. Therefore, as shown in FIG. 7(b), the frequency spectrum has an upper sideband and a lower sideband centered around a frequency that is an integral multiple of fs. Since the upper limit frequency fc of the chroma signal is, for example, 600 KHz, which is greater than the allowable frequency of 350 KHz, the sampling frequency fs is located on the lower side than 2fc. Therefore, the baseband chroma signal and
The chroma signal of the lower sideband centered at fs is partially superimposed, resulting in a state where so-called sub-Nyquist sampling is performed.

The sampled chroma signals shown by spectra A and B in FIG. 7(b) are 1/2 f
The band is limited so that only frequency components below s are passed. Therefore, the chroma signal of spectrum B having frequency components higher than 1/2 fs is blocked, and the sampling frequency f
Among the lower sideband components of s, a signal indicated by spectrum C is given to the encoder circuit 7 together with the signal A. Incidentally, since the frequency spectra A and C of the chroma signal are sampled signals, they are line spectra. At this time, each peak of the spectrum C in the lower sideband is located between the peaks of the spectrum A in the upper sideband of the baseband. Next, the chroma signal limited to the 1/2 fs band is turned into a 3.58 MHz chroma signal C2 again by the encoder circuit 7, and is recorded on the magnetic tape.

FIG. 6(b) is a block diagram showing the configuration of a reproduction system chroma signal sampling circuit. The chroma signal C3 reproduced from the magnetic tape is demodulated by the decoding circuit 8 and becomes color difference signals RY and BY, whose frequency spectra become A and C shown in FIG. 7(c). Next, these color difference signals are passed through an LPF9 with a passband of 1/2 fs or less.
After passing through, the signal is applied in parallel to a vertical correlation detection circuit 10, a re-sub-Nyquist sampling section 11, and a comb filter 12, respectively. The vertical correlation detection circuit 10 has the same function as the vertical correlation detection circuit 3 in FIG.
3 common terminal 13c is switched to the sub-Nyquist sampling section 11, and when there is no correlation between the two chroma signals, it is switched to the comb filter 12 side. In the re-sub-Nyquist sampling unit 11, FIG.
) The chroma signal obtained from the LPF 9 is sampled using the same sampling clock as the sub-Nyquist sampling section 4. Among the adjacent horizontal scanning lines, the chroma signal of the preceding scanning line is delayed by one horizontal scanning period (1H), and the chroma signal of the succeeding scanning line is sampled with a half period delay. These two chroma signals are superimposed, and as shown in Fig. 7(d), the lower sideband spectrum C is folded back to the higher frequency side with 1/2 fs as the axis of symmetry, and the envelope forms a spectrum D that is continuous with spectrum A. Form. In this way, a chroma signal having almost the same frequency spectrum as the original chroma signal shown in FIG. 7(a) will be obtained. On the other hand, even if there is no correlation between the chroma signals of adjacent scanning lines, the chroma signals may be erroneously sub-Nyquist sampled in the recording circuit. Therefore, when there is no correlation, the selector switch 13 is set to the comb filter 1.
2 side and converts the color difference signal from the LPF 9 into a conventional chroma signal. The reproduced chroma signal passes through the LPF 14 whose passband is equal to or less than fs, and is again turned into a 3.58 MHz chroma signal C4 by the encoder circuit 15 and output to a TV or the like.

However, when a magnetic tape having a narrowband chroma signal recorded in a conventional manner is played back by a VTR having the above-mentioned sub-Nyquist sampling circuit,
The reproduced chroma signal passes through the re-sub-Nyquist sampling section 11 shown in FIG. 6(b). Such signal processing is not necessary for magnetic tapes recorded using the conventional method, and there is a problem in that the reproduced image quality of the magnetic tape deteriorates when the signals pass through the re-sub-Nyquist sampling section 11.

The present invention has been made in view of these problems, and it is possible to prevent deterioration of the reproduced image quality even on magnetic tapes recorded using the conventional method without passing the chroma signals through the re-sub-Nyquist sampling section. The technical challenge is to

[0009]

[Means for Solving the Problems] The present invention is a chroma sub-Nyquist sampling circuit for a magnetic recording and reproducing device that expands the frequency band of a chroma signal recorded and reproduced on a video track of a magnetic tape. a recording system sub-Nyquist circuit, which is provided in , an audio signal processing circuit that records an identification signal of a constant frequency along with the audio signal on the audio track of the magnetic tape, an identification signal detection circuit that detects the presence or absence of an identification signal of a constant frequency recorded on the audio signal track, and a playback side. A reproduction system re-sub-Nyquist circuit, which is provided in the signal processing circuit, samples the chroma signal reproduced from the video track at the same speed as the recording system sub-Nyquist circuit, and expands the band of the reproduced chroma signal to the upper sideband of the permissible band. and a switching means for switching between the reproduced chroma signal and the chroma signal outputted via the reproduction system re-sub-Nyquist circuit in accordance with the output of the identification signal detection circuit.

0010

[Operation] According to the present invention having such characteristics, when a chroma signal from a tuner is input to the recording sub-Nyquist circuit, signal components exceeding the allowable recording band of the chroma signal are sampled so as to be folded back within this band. . Also, an identification signal having a constant frequency is generated and recorded on the track of the magnetic tape together with the audio signal. The sampled chroma signal is recorded on a magnetic tape via a video head. On the other hand, when the chroma signal reproduced from the magnetic tape is supplied to the reproduction system re-sub-Nyquist circuit, the chroma signal is reproduced in a band wider than the allowable band of the magnetic tape. Further, when an identification signal of a constant frequency is detected from the audio head, a wideband chroma signal can be obtained by selecting the output of the reproduction system re-sub-Nyquist sampling circuit by the switching means. When this identification signal is not detected, it is determined that the tape is a conventional magnetic tape, and the reproduced chroma signal can be directly output.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a chroma sub-Nyquist sampling circuit according to the present invention. (a) shows a chroma signal sampling circuit for the recording system, and (b) shows a chroma signal sampling circuit for the reproduction system. In FIG. 1A, a chroma signal C1 separated from the video signal and having a center frequency of 3.58 MHz is applied to a recording sub-Nyquist circuit 20. In FIG. The recording sub-Nyquist circuit 20 is a circuit that samples at a frequency lower than twice the highest frequency component of the occupied band of the chroma signal, and its configuration is the same as that in FIG. 6(a), so a detailed explanation will be given below. Omitted. On the other hand, the luminance signal Y is applied to a horizontal synchronizing signal separation circuit 21, where the horizontal synchronizing signal H is separated and applied to the LPF 22. The LPF 22 extracts the fundamental frequency component from the horizontal synchronization signal H, uses the sine wave signal V as an identification signal, and transmits it to the VT along with the 2-channel FM-modulated audio signals A1 and A2.
This circuit is provided to the R audio head 23.

In FIG. 1(b), the chroma signal C6 reproduced from the magnetic tape is transmitted to the reproduction system re-sub-Nyquist circuit 2.
4 or directly to the terminal 25 of the changeover switch 25.
a, 25b. Among the chroma signals of adjacent horizontal scanning lines, the reproducing sub-Nyquist circuit 24 delays the chroma signal of the preceding scanning line by 1H and samples it with the same clock as that of the recording sub-Nyquist circuit 20. This circuit samples the signal using a clock delayed by half a period, and superimposes these two sampled chroma signals to demodulate the original signal. Since its configuration is also the same as that in FIG. 6(b), detailed explanation will be omitted. On the other hand, the audio signal reproduced from the audio head 23 is given to the LPF 26. LPF26
is a circuit that passes components lower than the carrier frequency of the FM audio signal, and its output is given to the identification signal detection circuit 27.

FIG. 2 shows an example of a specific configuration of the identification signal detection circuit 27. As shown in FIG. In this figure, comparator 31
has an identification signal V and a reference voltage E at the inverting and non-inverting inputs.
1 is given to each. The comparator 31 compares the voltage of the input signal with the reference voltage E1, and its output is given to the transistor 32. The transistor 32 converts this identification signal V into a rectangular wave and supplies it to the charging/discharging circuit 33 . The charging/discharging circuit 33 is a circuit that applies an input rectangular wave to a charging/discharging capacitor 33a and a resistor 33b, and repeats charging/discharging every 1H period. The signal converted into DC by the charge/discharge circuit 33 is input to the inverting input section of the comparator 34 . Comparator 34
Similar to comparator 31, this input signal is compared with reference voltage E2, and its output is given to transistor 35. The transistor 35 converts the signal from the comparator 34 into L and H levels and outputs a switching signal S. This switching signal S is applied to the changeover switch 25 in FIG. 1(b), and two inputs are selected. The switching circuit 25 is LP
Together with F26 and the identification signal detection circuit 27, it constitutes a switching means that switches the chroma signal depending on the presence or absence of the identification signal.

The operation of the chroma sub-Nyquist sampling circuit of this embodiment configured as described above will be explained. When recording a chroma signal on a magnetic tape, for example, a chroma signal C1 having an occupied band of 350 KHz or more is used.
When the signal is applied to the recording sub-Nyquist circuit 20 of FIG. 1(a), it is first sampled with a 13.5 MHz clock. FIG. 3A is an explanatory diagram showing a state in which chroma signals of adjacent scanning lines are sampled. The chroma signal sampled at this frequency is further divided into 16, and the chroma signal is extracted at each first clock on odd scanning lines indicated by N-1 and N+1 lines. Also N
In the even-numbered scanning lines indicated by lines, chroma signals are extracted at each 8th clock, and chroma signals sampled at checkered positions within the same field are obtained. In FIGS. 7A and 7B described above, the sampling frequency fs is a frequency lower than twice the upper limit frequency fc in the band occupied by the chroma signal. Therefore, the frequency band of the sampled chroma signal is
Frequency (fs, 2fs, 3fs,...
The spectral components located in the lower sideband and upper sideband of .) are in a state where they overlap with each other. Spectra A and C are line spectra because they are sampled chroma signals. Even if spectrum C, which is obtained by folding spectrum B with 1/2 fs as the axis of symmetry, is superimposed on spectrum A, the sampling period of the chroma signal in each scanning line is shifted by 1/2 period, so it exists in the same sideband. The peaks of each spectrum do not overlap with each other. The chroma signal C5 band-limited at the frequency of 1/2 fs in this manner is applied to the terminal 5a of the changeover switch 5 shown in FIG. 6(a). If there is a vertical correlation, this signal is outputted as a color signal C5 for recording via the LPF 6 and the encoder circuit 7, and if there is no correlation, the color signal is outputted via the LPF 6 and the encoder circuit 7 without passing through the sub-Nyquist sampling section 4. It is output as signal C5.

On the other hand, the horizontal synchronizing signal H is separated from the luminance signal Y input to the horizontal synchronizing signal separation circuit 21, and the horizontal synchronizing signal H is
An identification signal V having the same period as the horizontal synchronizing signal H is obtained via F22. FIG. 4 shows the frequency spectrum of the signal input to the audio head 23 of the VTR, in which the identification signal V having the horizontal synchronization frequency fh is on the low frequency side, and the carrier wave frequency of the two audio signals is on the high frequency side. Audio signals A1 and A2 that are FM-modulated centering on fa1 and fa2 are shown, respectively. These signals are simultaneously applied to the audio head 23 and recorded in the deep portion of the magnetic tape.

Next, as shown in FIG. 1(b), the chroma signal C6 reproduced from the magnetic tape is given to the reproduction system re-sub-Nyquist circuit 24, and is again given a clock having the same timing as the recording system sub-Nyquist circuit 20. sampled. FIG. 3(b) is an explanatory diagram showing sampling points of chroma signals of adjacent scanning lines in this sampling circuit. The chroma signals of even lines indicated by N-2 and N lines are obtained from each one of the 16 divided sampling points.
The chroma signal of the odd line indicated by the N-1 line is extracted at the timing delayed by 8 clocks. The N-1 line chroma signal is delayed by a 1H delay circuit (not shown), and the N-1 line chroma signal is delayed by a 1H delay circuit (not shown).
One line of chroma signal is inserted. This synthesized chroma signal is applied to the terminal 25a of the changeover switch 25. This chroma signal is generated from the state shown in FIG. 7(c) by folding only the spectrum C into its upper sideband with 1/2 fs as the axis of symmetry.
, D, resulting in a chroma signal C7.

On the other hand, the audio head 2
The identification signal V is separated from the audio signal reproduced from 3,
It is input to comparator 31 in FIG. Incidentally, FIG. 5 is a diagram showing the waveform of each section when the identification signal V is input to the identification signal detection circuit 27 shown in FIG. When the identification signal V shown in FIG. 5A is detected from the magnetic tape, its level is compared with the reference voltage E1 of the comparator 31, and the transistor 32
A rectangular wave as shown in (b) is obtained. This rectangular wave is further input to the charging/discharging circuit 33 to obtain a signal waveform having a DC component as shown in (c). This signal is applied to a comparator 34 and compared with a reference voltage E2. Therefore, a switching signal S having an H level is applied to the changeover switch 25 from the output terminal of the identification signal detection circuit 27. At this time, the changeover switch 25 switches the common terminal 25c to the terminal 25a. In this way, the reproduced chroma signal C6 will be re-sub-Nyquist sampled and will be 3.58 again.
A chroma signal having a center frequency of MHz is output. Furthermore, when reproducing a magnetic tape recorded using the conventional method that does not have the identification signal V, the switching signal S is not generated from the identification signal detection circuit 27, so the common terminal 25c is switched to the terminal 25b, and the chroma signal C6 is not generated. I try to take it out directly. The chroma signal C7 output from the changeover switch 25 is then given to a video display unit such as a TV. In this embodiment, the identification signal V is shaped from the horizontal synchronization signal, but it goes without saying that a signal having a constant frequency can be used as the identification signal.

[0017]

As described above, in the chroma sub-Nyquist sampling circuit of the present invention, an identification signal indicating that a chroma signal is sub-Nyquist recorded on a magnetic tape is simultaneously recorded together with an audio signal, and this identification signal is used during playback. The detected and reproduced chroma signal is subjected to re-sub-Nyquist sampling processing. Furthermore, when reproducing a magnetic tape having a conventional chroma signal, the signal can be output without passing through the re-sub-Nyquist circuit of the reproducing system. Therefore, by recording sub-Nyquist sampling of chroma signals, it is possible to improve the image quality of a VTR, and even when playing back magnetic tape recorded using the conventional method, the circuit of the present invention can be used without deteriorating the image quality. You can get the effect that you can.

[Brief explanation of drawings]

FIG. 1 shows the configuration of a chroma sub-Nyquist sampling circuit in an embodiment of the present invention, in which (a) shows a recording system;
b) is a block diagram of a reproduction system chroma signal sampling circuit.

FIG. 2 is a circuit diagram showing the configuration of an identification signal detection circuit included in the chroma sub-Nyquist sampling circuit of the present invention.

FIG. 3 is an explanatory diagram showing a state in which chroma signals of adjacent horizontal scanning lines are sampled in a recording and reproducing system.

FIG. 4 is a spectrum diagram showing the frequency distribution of signals recorded and reproduced in the audio head in this embodiment.

FIG. 5 is a signal waveform diagram of the identification signal detection circuit in this embodiment.

FIG. 6 is a block diagram showing an example of a recording circuit and a reproduction circuit that perform sub-Nyquist sampling of a chroma signal.

FIG. 7 is a frequency spectrum diagram of signals in each block of the chroma sub-Nyquist sampling circuit.

[Explanation of symbols]

20 Recording sub-Nyquist circuit 21 Horizontal synchronization signal separation circuit 22, 26 LPF 23 Audio head 24 Reproduction system re-sub-Nyquist circuit 25 Selector switch 27 Identification signal detection circuit 31, 34 Comparator 32, 35 transistor 33 Charge/discharge circuit C1, C5, C6, C7 Chroma signal V Identification signal

Claims (1)

[Claims] 1. A chroma sub-Nyquist sampling circuit for a magnetic recording and reproducing device that expands the frequency band of a chroma signal recorded and reproduced on a video track of a magnetic tape, the circuit comprising:
Provided in the recording side signal processing circuit, the chroma signal is sampled at a frequency that is twice or less than the highest frequency of the chroma signal, and the component of the chroma signal that is above the allowable recording frequency band is sampled at a specific frequency below the allowable recording frequency band. a recording system sub-Nyquist circuit that folds back into the area, an audio signal processing circuit that records an identification signal of a constant frequency along with the audio signal on the audio track of the magnetic tape, and detects the presence or absence of an identification signal of a constant frequency recorded on the audio signal track. and an identification signal detection circuit provided in the reproduction side signal processing circuit, which samples the chroma signal reproduced from the video track at the same speed as the recording system sub-Nyquist circuit, and converts the reproduced chroma signal into an upper wave of the allowable band. a reproduction system re-sub-Nyquist circuit for widening the band to a sub-Nyquist circuit; and a switching means for switching between the reproduction chroma signal and the chroma signal outputted via the reproduction system re-sub-Nyquist circuit in accordance with the output of the identification signal detection circuit. A chroma sub-Nyquist sampling circuit comprising: