JPS5816797B2 - NTSC line sequential magnetic recording and reproducing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an NTSC line-sequential magnetic recording and reproducing system for magnetically recording and reproducing NTSC color television signals line-sequentially.

Conventionally, in the case of a video tape recorder (VTR) in which a color television signal according to the NTSC system is magnetically recorded and reproduced, the (R-Y) axis and (
Since it was configured to perform modulation and demodulation on two mutually orthogonal axes (B-Y), when reproducing it, the '141g1J signal was extracted to identify the phase of the two axes mentioned above, and this signal was used as the base. Determine the demodulation axis and perform demodulation to generate simultaneous signals and original line sequential NTSC
I was trying to revert to a color television signal.

With the above configuration, the discrimination signal detection circuit may malfunction due to dropouts or other noise components during playback, resulting in incorrect identification of the (R, -Y) and (B-y) axes, and color errors. There were drawbacks such as an inversion phenomenon.

The above-mentioned color reversal phenomenon has a great influence especially in the slow motion and steady modes of simple VTRs that are becoming widely used in general households.

The present invention has been made to eliminate the above-mentioned drawbacks, and is capable of magnetically recording and reproducing carrier color signals of a color television signal according to the NTSC system in a line-sequential manner. Four carrier waves shifted by 90 degrees in a fixed direction (counterclockwise on the coordinates) are switched and inserted for each horizontal scanning line, and this carrier color signal is detected and sequentially converted into a signal to generate the required signal. To provide an NTSC line sequential magnetic recording and reproducing system in which the inserted carrier waves whose phase differs by 90 degrees are balanced-modulated by this signal after passing through a transmission line, and are converted into simultaneous signals via a comb filter. With the goal.

An embodiment of the present invention will be described below with reference to the drawings.

This method performs detection using four axes that are shifted in a fixed direction (counterclockwise on the coordinates) by 90 degrees for each horizontal scanning line, and modulates this detection signal to return it to the original NTSC signal. The principle will be explained with reference to FIG.

In FIG. 1, U and V are two arbitrary axes that are orthogonal to each other, but for convenience of explanation, the U axis is the real axis and the V axis is the imaginary axis.

Color television signal C on orthogonal coordinates in Figure 1
is expressed as C-α+jβ.

Next, change the detection axis to U, V, -U, -V,
When detection is performed by sequentially switching U, . . . , the detection output changes as follows.

α (IH), β (2H), -α (3H), -β (4H)
,α,・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・(1) At this time, the detection axes that change by 90 degrees are ■, j, -1, -j, 1, etc. ...
Since it is expressed as (2), if the signal on this axis is subjected to AM modulation using the above signal, the following will be obtained.

α, jβ, α, jβ, α, ・・・・・・・・・・・・
(3) Here, when the signal in equation (a) 3) is delayed by the IH period, the following is obtained.

jβ, α, jβ, α, jβ, ・・・・・・・・・・・・
・・・・・・・・・・・・・・・(4) Adding the signal in equation (3) and the signal in equation (4) obtained by delaying this by the IH period, the following is obtained. (It becomes.

α + j β, α + j β, α + j β, α + j β, ...
・・・・・・・・・・・・(5) Equation (5) shown above is
This is nothing but a simultaneous signal expressing the color television signal C mentioned above.

In the above explanation, equation (2) represents the detection axis starting from the U axis on the coordinates in Figure 1, but it may also start from any axis X; in this case, (2)
The formula is Xl jX, -Xl-jX, Xl...

Therefore, equation (5) in this case is X(α+jβ), X(α
10jβ), X(α10jβ), ..., and the first
The only difference is the overall angle on the coordinates shown in the figure, and this only means that the phase with the original signal changes, and does not cause any problems.

Next, the implementation of this method will be described with reference to the block diagram shown in FIG.

FIG. 2 schematically shows a recording and reproducing system for magnetically recording and reproducing NTSC color television signals using this method.

During recording, the input NTSC color television signal is separated into two systems, a luminance signal and a chromaticity signal, as is well known (the luminance signal is passed through a low-pass filter,
The chromaticity signals are each extracted by a bandpass filter or the like, but are omitted from illustration.

), the luminance signal and chromaticity signal are mixed again after passing through the respective required transmission paths and are recorded on a magnetic tape as a recording medium.

The luminance signal component in the input NTSC color signal is level-controlled by the AGC circuit 1, passes through the above-mentioned transmission path, and then is converted to a high frequency signal by the frequency modulation circuit 2 and mixed. This leads to circuit 6.

On the other hand, the chromaticity signal component is also level-controlled by the ACC circuit 3 in the same way, passes through the above-mentioned transmission path, is converted to a low frequency signal by the phase detection circuit 4 and the frequency modulation circuit 5, and is guided to the mixing circuit 6. After being mixed with the luminance signal component described above, it is supplied to the magnetic head 8 via the recording amplifier 7 and recorded on the magnetic tape.

The signal that has passed through the ACC circuit 3 includes a burst signal as color information, and as explained below, four inserted carrier waves whose phase is shifted in a fixed direction by 90 degrees for each In are inserted into each In. The burst signal is applied to the oscillator 20 in such a manner that the burst signal is switched to the oscillator 20.

Although not shown, an AC extracts a burst signal from the chromaticity signal supplied through a bandpass filter using a burst pulse supplied from a synchronization separation circuit.
There is a C detection circuit, which extracts a control voltage corresponding to the level of the burst signal and supplies it to the ACC circuit 3, so that the output of the ACC circuit 3 is controlled to be constant.

During this recording, the output from the above-mentioned mixing circuit 6 is on line 26 (this is the EE mode signal line).

) is supplied to the synchronization signal separation circuit 25, where the horizontal synchronization signals for the entire scanning period are separated.

The horizontal synchronization signal is supplied to the AFC circuit 24 to stabilize the horizontal synchronization signal including the vertical synchronization signal period (this period also includes an equalization pulse).

The signal from the AFC circuit 24 is sent to the pulse generator 2
3, which forms a gate pulse every %fh for extracting the burst signal inserted into the back porch of the synchronizing signal through means such as counting and frequency division, and supplies it to the switch circuit 22.

In the oscillator 20, 3 and 5 included in the output of the ACC circuit 3
It performs oscillation in synchronization with a burst signal of 8 MHz component, and transfers it to four phases (0°, 90°, 180°) in the transfer circuit 21.
, corresponding to 270°) and the switch circuit 22
The detection axis of the phase detection circuit 4 is switched by 90 degrees for each IH in synchronization with the gate pulse from the pulse generator 23.

The oscillator 20 described above is configured to oscillate at a stable frequency of 3.58 MHz in synchronization with a stable burst signal during reproduction.

Further, the oscillator 20 can achieve more stable synchronization by forming a continuous control loop using an APC loop or the like.

During playback, the recorded signal on the magnetic tape is taken out by the magnetic head 8, amplified by the playback amplifier 9, and then the luminance signal and chromaticity signal are separated into two systems, and the respective transmission paths are connected. After passing through, add the above two signals again to get the original N
This is a TSC color signal.

The luminance signal is taken out via a bypass filter 10, noise components and other unnecessary components are removed by a limiter circuit 11, and then demodulated by a demodulation circuit 12 to restore the original signal and guided to an addition circuit 19.

On the other hand, the chromaticity signal is extracted via a low-pass filter 13, passed through a limiter circuit 14, and then demodulated by a demodulation circuit 15.

Using the demodulated signal from the demodulation circuit 15, the next-stage balanced modulation circuit 16 performs balanced modulation on the carrier signal from the switch circuit 22 described above.

In this case as well, the formation of the carrier wave signal from the switch circuit 22 is the same as that during recording, so a description thereof will be omitted.

The signal from the balanced modulation circuit 16 is directly led to the subtraction circuit 18, and at the same time, it is also led to the subtraction circuit 18 via the IH delay circuit 17.

From the above balanced modulated signal, the balanced modulated signal is
A simultaneous signal is obtained by subtracting the signal delayed by H.

The luminance signal and chromaticity signal obtained as described above are added together by an adder circuit 19 and extracted as an original NTSC color signal.

As described above, according to the method of the present invention, not only can the color reversal phenomenon be prevented, but also the 90°
Since the modulation and demodulation are performed by an axis that changes in degrees, there is no need to detect a discrimination signal.When the detection signal is averaged over 4H, the DC component becomes zero, so a DC component regeneration circuit is not required. NTS is simple and has great effects.
A C-line sequential magnetic recording and reproducing system can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the method of the present invention, and FIG. 2 is a block diagram showing a magnetic recording/reproducing system for implementing the method of the present invention. 20...3.58MHz oscillator, 21...
...Phase shift circuit, 22...Switch circuit, 23.
...Pulse generator, 24...AF
C circuit, 25...Synchronization signal separation circuit.

Claims (1)

[Claims] I NTSC color television 1. In a device that records and reproduces a color television signal on a recording medium, four color subcarriers whose phases are shifted by 90 degrees in a fixed direction obtained from the input color television signal are switched for each IH period to generate a carrier color signal. The detected signals are recorded as sequential signals on the recording medium, and the recorded sequential signals are used to balance-modulate the color subcarriers having a phase difference of 90 degrees, and the output signals are passed through a comb filter to reproduce simultaneous signals. An NTSC line sequential magnetic recording and reproducing system characterized by: