JPS6122391Y2 - - Google Patents

Description

[Detailed description of the invention] The invention relates to a SECAM signal magnetic recording device,
In particular, when performing high-density H alignment recording of SECAM signals field by field using an azimuth recording method, etc., after converting the chroma signal into low frequency subcarriers having different 1/4 fH phases for each adjacent field, for example, Mix with FM luminance signal and record
In a SECAM signal magnetic recording device, by aligning the phases of the low-range color subcarrier signals in advance and keeping the low-range color subcarrier signals recorded on adjacent tracks in an interleaved relationship with each other, crosstalk during playback can be avoided. The object of the present invention is to obtain a SECAM signal magnetic recording device which performs recording while eliminating the influence of color and has good color reproducibility.

It is called the so-called β method or VHS method.
The azimuth recording method used in VTRs uses magnetic heads with different inclinations of magnetic gaps to record signals in one field, for example, without providing a guard band between adjacent recording tracks, or by partially overlapping them. This is a method in which recording is performed sequentially in units of tracks, and in the high frequency range, the azimuth loss of the magnetic head is effectively utilized, and crosstalk between adjacent tracks can be practically eliminated.

However, in the region of low-range color subcarrier signals, the influence of crosstalk cannot be avoided because the azimuth loss with respect to the reproduced signals of adjacent recording tracks is insufficient. For this reason, a so-called H alignment recording method is adopted in which the horizontal synchronization signals of signals recorded on adjacent recording tracks are aligned, and the phases of the subcarriers of the chroma signals to be low-frequency converted are mutually adjusted to 1/4fH (however, fH is horizontal By shifting the subcarrier phase of the restored chroma signal during playback by the frequency of the synchronization signal, the phase of the subcarrier of the restored chroma signal is in the same phase relationship for the signal that should originally be played in the playback signal, but is reversed every 1H for the crosstalk signal. A method is adopted in which only the Frostoff component is removed by selecting the frequency of the idling signal so that it has a phase relationship, and passing it through a comb-type filter equipped with a 2H delay line (where H is the horizontal scanning time). It is possible that

By the way, in the SECAM signal, as is well known, the color signal is line sequential. For example, in the n-th scanning line, the (B-Y) signal is generated using 272fH as the FM subcarrier, and in the (n+1)th scanning line, the (B-Y) signal is (RY) signals are alternately transmitted using 282fH as a subcarrier.
The FM modulator on the transmitting side is start-stop driven for each line, and each FM signal is
Since it has a phase correlation with the signal 1H before, its frequency distribution is discrete, and basically the above-mentioned interleaved recording method can be used.

However, in the SECAM signal, the phase of one color subcarrier of a set of three scanning lines is set to 0, 0, π (π , π, 0). Therefore, the long-term average
The frequency spectrum of the SECAM signal is distributed at fH/3 intervals, but in addition to the fact that the color difference signals transmitted alternately on the scanning lines are distributed at fH/2 intervals, the frequency spectrum is eventually distributed at 11/6 fH intervals. It turns out.

Record and play back such signals, and remove the crosstalk.
It is theoretically conceivable to use a comb-type filter with a 6H delay line to remove the light, but this would result in poor color reproduction and fidelity and would be impractical.

In view of this, the present invention has been developed based on the above-mentioned recording method, and has an improved circuit configuration for aligning the phases of subcarriers during recording in the process of low-frequency conversion of the chroma signal of the SECAM signal. This is a proposal.

Below, the details of this invention are explained on the implementation circuit side (recording system).
This will be explained with reference to FIG. 1, which shows the system, and FIG. 2, which shows the same (reproduction system).

In the embodiment shown in Fig. 1 (recording system), only the main part of the low-frequency conversion part of the chroma signal is processed, and in the embodiment shown in Fig. 2 (reproduction system), only the main part of the inverse conversion part of the reproduced chroma signal is processed. Each is characteristically represented by a block diagram.

In FIG. 1, figure number 1 indicates the input terminal of the SECAM (composite) signal. The chroma signal separation circuit indicated by 1 is equipped with a bell filter, a limiter, etc., and supplies the separated FM subcarrier component to the first frequency conversion circuit 2 for low frequency conversion. 3 is a non-modulated carrier separation circuit, which is a type of gate that extracts the non-modulated carrier that is inserted for 4.5 μsec from the back porch of the horizontal synchronization signal of the SECAM signal to the beginning of the image signal in order to use it as a reference for the non-coloring level. It is made up of circuits.

The first oscillator 4 and the second oscillator 5 can each be of the injection type, clamp type or injection type, with the former being a 272fH unmodulated carrier only, and the latter being a 282fH unmodulated carrier.
It resonates only with the unmodulated carrier of , and starts and stops driving alternately every section 1H in which the unmodulated carrier that should resonate exists. Start and stop control can be performed using a switching circuit controlled by a 1H width rectangular pulse.

Reference numeral 6 indicates a switching control circuit that enables a bistable circuit, and controls an electronic switch 7 synchronously to control the output of the oscillator in operation among the first and second oscillators 4 and 5 to the second oscillator. It is added as one input to the two-frequency conversion circuit 8. The bistable circuit is basically triggered by the horizontal synchronization separation signal separated and extracted by the synchronization separation circuit 9, and is configured to use the 1/2 frequency-divided output as a control signal. To prevent malfunction (reversal) due to other causes,
Separately, the output of the non-modulated carrier separation circuit 3 is input, and the circuit is connected so as to be reset by the output of an FM detection circuit 10 that detects the difference in carrier frequency.

Reference numeral 11 denotes a PLL oscillation circuit constituting another input signal source of the second frequency conversion circuit 8, which alternately generates (44+1/8) fH for each field using the output horizontal synchronization signal of the synchronization separation circuit 9 as a reference signal. , (44−1/8)
It is configured to generate a phase-locked oscillation output of fH. The chroma signal applied to the first frequency conversion circuit 2 is a line-sequential FM color difference signal, and the phase of the carrier is 00π (or ππ) every three lines.
0), the transmission is switched.

Since the phase of the unmodulated carrier in the SECAM signal is also switched and transmitted as 00π (or ππ0), the outputs of the first and second oscillation circuits 4 and 5 also reproduce the same phase change. becomes. Furthermore, since the bistable circuit 6 is configured to be triggered by the horizontal synchronizing signal and reset by the output of the FM detection circuit 10 as described above, the first , the color order and switching phase of the outputs of the second oscillators 4 and 5 are determined by the color order of the chroma signal (for example, D _B ', D _R ', D _B ', D
_R '...) and the switching phase (00π...) exactly match.

Therefore, the output of the electronic switch 7 and the PLL
The output of the second frequency conversion circuit 8 whose multiplication input is the output of the oscillation circuit 11 is Vi=βcos(W _I +(44±1/8)W _H・t} (1) or Vi=βcos (W _I + (44±1/8) W _H・t+π} (2) Here, W _I is W _B =272fH (≒4.25MHz) W _R =282fH (≒4.40625MHz) (1) is the same phase, (2) represents the signal waveform when the phase is reversed. Now considering the case where the input chroma signal is monochromatic, the output V _C of the chroma signal separation circuit 1 is as follows: V _C = AsinWct (1)' V _C = Asin ( Wct+π) (2)′.

Since the contents of equations (1) and (1)' and (2) and (2)' correspond in time, the output of the first frequency conversion circuit 2 (which functions as a multiplier) is filtered by a low-pass filter. If _only the difference _output component _{is taken} out through
As shown in (3), the switching phases of the (low-band converted) subcarrier signals in the low-band converted chroma signal are all in phase in any period. The low-frequency conversion signal V _SL expressed by the above equation (3) is applied to the magnetic head (H) in a frequency-multiplexed form with a luminance signal component that is separately FM-modulated, and is recorded on the magnetic tape (T). .

Next, the block diagram of the reproduction system shown in FIG. 2 will be explained.

The figure shows a chroma signal separation circuit 21 that extracts a low-frequency converted chroma signal from a reproduced signal, and a separated low-frequency converted chroma signal V _SL and the output of an idling signal generation circuit 30 as two inputs. First frequency conversion circuit 2 that beats up the chroma signal
2 and 2H comb filters 23 are the basic constituent elements.

The idling signal generation circuit 30 individually
First and second crystal oscillators 31 and 32 that oscillate at frequencies of 272fH and 282fH, an electronic switch 34 that switches the output of both oscillators and applies it as one input to the second frequency conversion circuit 33, and an FM brightness signal demodulation circuit 35. It is triggered by the output (horizontal synchronization signal) of the synchronization separation circuit 36 that separates the horizontal synchronization signal from the output, and during the output of the 2H comb filter 23, the field ID
FM detection circuit 35 that detects changes in the frequency of the trapezoidal wave ID (discrimination) signal inserted over 9 lines (7 to 15H and 320 to 328H) during the vertical retrace period extracted by the separation circuit 37; The bistable circuit 37 is configured to be reset by the output of the electronic switch 34, and the output horizontal synchronization signal of the synchronization separation circuit 36 is used as a reference signal, and (44+1/8)fH is set for each field. Or (44
-1/8) fH, and its output is applied to the second frequency conversion circuit 33 as another input.

With this configuration, the low frequency converted chroma signal contained in the output of the reproducing magnetic head (Hp) is separated by the chroma signal separation circuit 21 and upcompressed in the first frequency conversion circuit 22.
As mentioned above, the switching phases of the subcarriers of the low-frequency converted chroma signal are aligned as (000), so the frequency spectrum has the relationship as shown in Figure 3 A (however, A and B are adjacent (represents the frequency spectrum of the reproduced signal of tracks A and B). Then, the output after the upcompartment is the third
The result is as shown in Figure 3B, so the high-frequency converted signal containing crosstalk is converted into a 2H signal with characteristics as shown in Figure 3C.
By passing the signal through a comb filter 23 based on a delay line, crosstalk can be completely removed and only the chroma signal (line-sequential color difference FM signal) of the track to be reproduced can be applied to the subsequent demodulation circuit. I can do it.

Since the bistable circuit 37 is configured to be reset in synchronization with changes in the field ID signal,
Color order for each field (D _R ′, D _B ′, D _R ′…)
The accuracy of is confirmed. By the way, field ID
If the bistable circuit is reset using only the signal identification output, if the bistable circuit 37 is reset due to noise or the like during one subsequent field, the color order will be disrupted, making it impossible to produce a correct color image. can't get it.

In order to prevent such a drawback, a configuration may be adopted in which the non-modulated carrier in a specific horizontal synchronization section is extracted and the bistable circuit 6 is also reset by its identification output (FM detection output).

Since the present invention has the above-described configuration, a comb-type filter based on a 6H delay line as in the conventional example, or a multiplication circuit and a low-pass filter that converts the chroma signal (color difference line sequential FM signal) separated from the SECAM signal in advance. This combination eliminates the need for a complicated circuit for in-phase conversion, and improves color reproducibility.

[Brief explanation of the drawing]

The drawings all relate to the SECAM signal recording device of the present invention; Figure 1 is a block diagram of the main parts of the recording system, and Figure 2 is a block diagram of the main parts of the recording system.
The figure is a block diagram of the main part of the reproduction system, and FIG. 3 is a diagram showing the spectral distribution of the main part output signal. 1... Chroma signal separation circuit, 2... First frequency conversion circuit, 8... Second frequency conversion circuit, 11...
PLL circuit, 4...first oscillator, 5...second oscillator, 6...bistable circuit.

Claims (1)

[Scope of utility model registration request] The different frequency output of the oscillator which is start-stop driven every horizontal scanning period by the unmodulated carrier separated from the SECAM signal to be recorded is
The frequency conversion circuit is switched by the output of a bistable multivibrator connected to be continuously triggered by the horizontal synchronization signal in the SECAM signal and set by the output of the FM detection circuit that identifies the unmodulated carrier. The chroma signal separated from the SECAM signal is converted to a low frequency by using the up-converted beat output as an idling signal. A SECAM signal magnetic recording device configured to mix this signal with an FM luminance signal and record it in units of one field.