JPH029756B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal conversion circuit used in a VTR that enables recording and playback of three color systems.

Currently, there are various systems for cassette-type VTRs that use a pair of magnetic heads with different azimuths to scan the tape diagonally to form a recording track for each field. Standardized and widespread. In other words, for VTRs that record NTSC color signals with a frame frequency of 30Hz and a scanning line count of 525 per frame,
A standard has been established to form a recording pattern in which the heads are opposed to each other at an angular interval of exactly 180° as shown in FIG. 1, and H alignment is applied between adjacent tracks as schematically shown in FIG. The frame frequency is 25Hz and the number of scan lines per frame is 625.
Record SECAM or PAL color signals for book use
For VTRs, the heads are installed only 0.5H or 17" away from the 180° angular spacing as shown in Figure 3, and the so-called H alignment with the adjacent azimuth track is achieved as shown in Figure 4. The standards to be applied have been established.

The reason why H alignment is applied to adjacent tracks with different azimuths when recording color signals is that the horizontal periodic signal part of the FM luminance signal is reduced, so unless special processing is performed, it will be reproduced as crosstock noise. This is because there is a risk of vertical bands appearing on the screen.

Record PAL and SECAM color signals below
The configuration of a VTR that has been improved to enable recording and playback of three color systems including NTSC color signals will be explained with reference to FIGS. 5 and 6. PAL
and VTR for recording SECAM color signals
The head is about 17' off from the 180° position,
When recording and playing back an NTSC color signal, the playback output must be delayed by a predetermined amount for every other field, and the amount of delay is 0.42H of the NTSC color signal.
(26.8μsec). Therefore, as shown in FIG. 5, when recording an NTSC color signal, the conventional recording circuit inputs the NTSC color signal at the output of the flip-flop 2, which is inverted at the output of the vertical synchronization separation circuit 1, for 26.8 μsec. The delayed output and non-delayed signal of the delay circuit 3 are alternately selected by the selection switch _S1 , and the switching output is delayed by 0.42H after one field. The switching output is separated into a luminance signal and a color signal via a low-pass filter 4 and a second band-pass filter 5, and the luminance signal is derived as an FM luminance signal via an AGC circuit 6, an FM modulation circuit 7, and a bypass filter 8. and the color signal is transmitted via the changeover switch S ₂ .
It is derived as a low frequency converted color signal via the ACC circuit 9 and the second frequency conversion circuit 10. derived
The FM luminance signal and the low-frequency conversion color signal are sent to the adder circuit 11.
The signals are added together and applied to the head via the recording amplifier 12.

In such a conventional circuit, the timing pulses for the AGC circuit 6 and ACC circuit 9 that process the signal after switching are obtained from the first horizontal synchronization separation circuit 13 that synchronously separates the switching output, but the horizontal synchronization for frequency conversion is The signal uses the horizontal synchronization separated output before switching, taking into consideration the followability of the oscillation circuit. That is, the AFC circuit described above uses the output of the second horizontal synchronization separation circuit 14, which inputs the signal before switching, to the 1/2H killer circuit 15.
The output of the voltage controlled oscillation circuit 17 is divided into a frequency corresponding to the horizontal synchronization period via the frequency dividing circuit 18, and the output is used as the comparison input for the voltage controlled oscillation circuit 16. It controls 17. The AFC output and the output of the 3.58MHz second oscillation circuit 19 are connected to the first frequency conversion circuit 20.
The signal is converted into a low frequency conversion carrier and inputted to the second frequency conversion circuit 10. Therefore, despite the misalignment of the heads, the NTSC color signal forms a recording pattern that is H-aligned according to the standard, with some exceptions. In Figure 5, figure number 21 indicates PAL and
A first bandpass filter 22 separates the SECAM color signal, and 22 represents a first oscillation circuit that generates PAL and SECAM subcarriers, respectively.

On the other hand, in order to play back the recorded NTSC color signal on a VTR whose head mounting position is slightly shifted,
The regeneration circuit of FIG. 6 is used. Playback amplifier 23
The playback output derived through the is input to the next stage high-pass filter 24 and low-pass filter 25.
Separated into FM luminance signal and low frequency conversion color signal.
The FM brightness signal is transmitted through the limiter 25 and the FM demodulation circuit 2.
26, the signal is converted into a luminance signal, and is inputted to the adder circuit 28 via the amplifier circuit 27, and the low frequency converted color signal is
The ACC circuit 29 is converted to a high frequency signal through a second frequency conversion circuit 30, and is input to the adder circuit ₂₈ through a second bandpass filter 31 that passes only the NTSC color signal. The addition output is
The addition output and its delayed output are alternately selected by the selection switch _S5 , which is input to the 26.8 μsec delay circuit 32 and is switched according to the output of the flip-flop 33, which is inverted by the control signal. The output of the AFC circuit and the output of the APC circuit, which are input to the first frequency conversion circuit 34 which synthesizes the high frequency conversion carrier input to the second frequency conversion circuit 30, are combined as follows. First, the APC circuit controls the burst gate 36 using the output of the first horizontal synchronization separation circuit 35 which receives the amplified output as input, and separates the burst signal from the second bandpass output.
The phase is compared with the output of the 3.58 MHz second oscillation circuit 38, and the second crystal oscillation circuit 39 is controlled according to the comparison output to derive the APC output via the changeover switch _S6 . On the other hand, the AFC circuit inputs the output after switching to the second horizontal synchronization separation circuit 42, removes the equivalent pulse in the 1/2H killer circuit 41, and uses it as the reference input of the comparison circuit 42, and performs voltage control controlled by the comparison output. The output of the type oscillation circuit 43 is inputted as an AGF output to the first frequency conversion circuit 34, and also inputted to a frequency dividing circuit 44 which divides the frequency into a frequency corresponding to the horizontal synchronization period, and uses the divided output as a comparison input. In addition, figure number 45 in the figure is 4.43M, which is close to the subcarrier frequency of PAL or SECAM.
A first oscillation circuit that inputs the Hz oscillation output to the comparison circuit 37 via the switch _S7 , 46 a first crystal oscillation circuit that derives an oscillation output with a center frequency of 4.43MHz based on the comparison output, 47 a SECAM young
Each shows a first bandpass filter that passes the PAL color signal.

The above-mentioned reproducing circuit also horizontally synchronizes and separates the outputs before and after switching, and has two horizontal synchronization separation circuits.

Therefore, in order to use only one horizontal synchronization separation circuit, the delay circuit in the recording circuit is arranged after the adder circuit 11, and the delay circuit in the reproduction circuit is arranged after the reproduction amplifier.
There is also a method of delay processing the FM modulated luminance signal,
In such a case, the signal band is as wide as 7MHz, and inexpensive delay means such as glass delay lines cannot be used, making it difficult to put it into practical use due to cost considerations.

Therefore, the present invention aims to propose an inexpensive color signal conversion circuit with a single horizontal synchronization separation circuit by proposing an AFC circuit that can follow discontinuous horizontal synchronization signals. .

The present invention will be explained below according to an embodiment shown in FIG. First, the circuit operation for recording an NTSC color signal using the circuit of this embodiment will be explained. The NTSC color signal to be recorded is
The signal is inputted to the delay circuit 48 via SW ₁ as in the conventional example, and is inverted for each field according to the output of the first flip-flop 50 which inputs the output of the vertical synchronization separation circuit ₄₉ . are selected alternately, and the luminance signal component is extracted through a low-pass filter 51, and the color signal component is extracted through a second band-pass filter 52 centered at 3.5 MHz. The luminance signal component is input to an addition circuit 56 via an AGC circuit 53, an FM modulation circuit 54, and a high-pass filter 55.
For color signal components, use mode switch SW ₃ , recording/playback switch
SW ₄ , ACC circuit 57 , second frequency conversion circuit 58
The added output is applied to the video head via a recording amplifier 59 and a recording/reproducing switch _SW5 . So NTSC recorded
The recording pattern of the color signal substantially corresponds to the standardized pattern, although it is discontinuous at a short period at the start of scanning compared to the standardized pattern.

The feature of this embodiment is that only discontinuous video signals after switching during recording are synchronously separated. That is, a horizontal synchronization separation circuit 60 inputs a switching output via a recording/playback switch (SW ₆ ).
inputs a horizontal synchronizing signal having a discontinuous point for each field to the AGC circuit 52, the ACC circuit 57, and the burst gate circuit 66 (described later).
It is used as a reference signal for the AFC circuit via the 2H killer circuit 61. Therefore, in this embodiment, the AFC circuit is required to be configured so that it can follow the horizontal synchronization signal which is discontinuous by 0.42H for each field.
Therefore, in this embodiment, the voltage controlled oscillation circuit 62 is
The frequency dividing period of the frequency dividing circuit 63 that frequency divides the AFC output is set to 1/2H, and the frequency divided output is used as a reference signal in the first comparator circuit 64. Therefore, in this embodiment in which the amount of variation at the discontinuity point is only 0.08H, the AFC output is kept in a steady state during the vertical blanking period. The above-mentioned AFC output is used as one input of the first frequency conversion circuit 65, and serves as the other input.
The APC output is derived as follows. That is, the burst gate circuit 66, which receives the ACC output via the recording/playback switch _SW7 , applies the burst signal as a reference signal to the second comparison circuit 67, and receives the APC output via the recording/playback switch _SW8 . The second comparison circuit 67, which uses the output as a comparison input, controls a second crystal oscillation circuit 68 that generates an APC output. Therefore, the 3.58MHz APC output generated by the second crystal oscillation circuit 68 is output by the mode switch.
is input to the frequency conversion circuit 65 via SW ₉ .
The above-mentioned first one which heterodyned the APC/AFC outputs
The output of the frequency conversion circuit 65 is applied to the second frequency conversion circuit 65 as a low frequency conversion carrier.

On the other hand, when reproducing an NTSC color signal, first the head output via the recording/playback switch SW ₅ is amplified by the reproduction amplifier 69, and then input to the low-pass filter 70 and high-pass filter 71 to produce a low-frequency conversion color signal.
Divided into FM converted luminance signal. The FM modulated luminance signal is
The signal is FM demodulated via a limiter 72 and an FM demodulation circuit 73, and is input to an adder circuit 75 via an amplifier 74.

In addition, the low frequency converted color signal is inputted to the ACC circuit 57 and the second frequency conversion circuit 58 via the recording/reproduction switch _SW4 , and is converted to a high frequency signal.
A second bandpass filter 7 whose center frequency is Hz
6. The signal is passed through a second comb-type filter 77 that removes low-range luminance components, and is then input to the adder circuit ₇₄ via the mode switch SW10. Therefore, the NTSC color signal obtained by addition and having discontinuous points for each field is input to the delay circuit 48 for continuousization. The changeover switch _SW2 , which receives delayed output and non-delayed output, performs switching according to the output of the first flip-flop 50, which is inverted for each field, and derives a continuous NTSC color signal.

The high-frequency conversion carrier input to the second frequency conversion circuit 58 is generated by heterodyne of the APC output and AFC output in the first frequency conversion circuit 65. The AFC circuit during playback is derived in the same manner as during recording based on the horizontal synchronization separation output before switching, and the APC output is input to the second comparison circuit 67 for comparison with the output of the second comb filter 77. , the second with a fixed oscillation output of 3.58MHz
It is derived using the output of the oscillation circuit 78 as a reference input.

The remaining drawing number 79 in Fig. 7 is the PAL and
The first band pass filter selects the color signal of the SECAM color signal, 81 is PAL and SECAM during playback.
A first band-pass filter 81 selects a color signal of the color signal; 81 is a first comb-type filter following the filter 80 and eliminates low-range luminance components;
When recording and playing back PAL and SECAM color signals
A first oscillation circuit that emits a fixed oscillation output of 4.43MHz,
SW ₁₂ is a mode switch that switches between the first and second oscillation outputs, and SW 83 is a mode switch that switches between the first and second oscillation outputs.
Crystal oscillation circuit, 84 is the recording/playback switch during playback SW ₁₃
A second flip-flop receives as a trigger input the output of the control head inputted through the flip-flop, and 85 represents a servo circuit that controls the tape running system based on the output of the first or second flip-flop.

The specific configuration of the AFC circuit of this embodiment will be explained below with reference to FIGS. 8 and 9. Furthermore, Figure 8 shows
Only the blocks necessary for recording and reproducing NTSC color signals are illustrated, and the illustrations of blocks necessary for processing PAL and SECAM color signals are omitted. In the illustrated embodiment, the oscillation frequency of the voltage controlled oscillation circuit 62 is made eight times the AFC output frequency and is inputted to the frequency divider circuit 63, while the first frequency conversion circuit 65 is inputted via the 1/8 frequency divider circuit 86. AFC (44 1/4) f _H (f _H is the horizontal synchronization frequency). Therefore, the frequency dividing circuit 63 divides the 350f _H derived by the voltage controlled oscillation circuit 62 into 1/3.
The frequency is divided by the 50 frequency divider circuit 63a, and the frequency is divided by the 50 frequency divider circuit 63a.
3b, the reference signal is converted to a frequency equivalent to 2f _H , and the reference signal obtained by inputting it to the reference signal generation circuit 64a in the comparison circuit 64 forms a slope with a period of 1/2H, as shown in FIG. 9A. do. Sideways
Even when the synchronously separated output containing a discontinuous point of 0.42H is used as a sampling pulse, the gate circuit 64b only samples the slope of the reference signal by only 0.08H, and the hold circuit 64c in the next stage fluctuates to the hold output c. However, the voltage controlled oscillation circuit 62 controlled via the loop filter 64d becomes stable within the vertical blanking period due to tracking. Therefore, according to this embodiment, 0.42H
The frequency fluctuation of the AFC output caused by the discontinuity point does not cause any problem in frequency conversion.

As mentioned above, according to the present invention, PAL and
When recording and reproducing standard patterns of NTSC color signals using a VTR with a head arrangement for recording SECAM color signals with H alignment, the AFC circuit for color signal processing can also follow discontinuous horizontal synchronization signals. Because of this configuration, only one horizontal sync separation circuit is required, which is very effective.

[Brief explanation of drawings]

Figure 1 is a standardized head layout for recording and reproducing NTSC color signals, Figure 2 is a schematic diagram of a synchronous recording pattern, and Figure 3 is a standardized head layout for recording and reproducing PAL/SECAM color signals. , 4th
The figure is a schematic diagram of the same recording pattern, FIG. 5 is a recording circuit block diagram of a three-system VTR, FIG. 6 is a reproduction circuit block diagram of the same, FIG. 7 is a circuit block diagram of an embodiment of the present invention, and FIG. The main circuit block diagram and FIG. 9 show waveform explanatory diagrams of FIG. 8, respectively. Explanation of main figure numbers, 60...Horizontal synchronization separation circuit,
64... (first) comparison circuit, 62... Voltage controlled oscillation circuit, 63... Frequency dividing circuit.

Claims (1)

[Claims] 1 A horizontal synchronization separation circuit that separates discontinuous horizontal synchronization signals as an AFC circuit whose signal input is a horizontal synchronization signal with approximately 1/2 horizontal synchronization period discontinuity, and a horizontal synchronization separation circuit that separates the discontinuous horizontal synchronization signal, and uses the synchronization separation output as the reference input and the oscillation output. A comparison circuit that uses the frequency output as a comparison input, a voltage-controlled oscillation circuit that controls the oscillation frequency based on the comparison output,
A color signal processing circuit comprising: a frequency dividing circuit that divides the frequency of the AFC output and generates the frequency-divided output equivalent to 1/2 the horizontal synchronization period.