JPS6132876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides at least PAL video signals and NTSC video signals.
The present invention relates to a video signal reproducing device capable of reproducing video signals.

In a helical scan VTR that can record and play back PAL (or CCIR) video signals,
In order to reduce crosstalk between adjacent tracks, the chroma signal on the A track is
1/8) f _H , and (44 + 1/8) on B track.
8) There is a known method in which frequency reduction conversion is performed to _fH ( _fH : horizontal frequency), recording chroma signals between adjacent tracks are frequency interleaved with each other, and the spectra are recorded in a separated state. During playback, a comb-tooth filter with passbands at 1/ _2fH intervals is used to remove crosstalk components from adjacent tracks with a 1/ _4fH frequency difference to obtain a high-quality playback image. .
Such a comb-tooth filter consists of a delay line with a delay amount of two horizontal intervals (2H) and an adder circuit that adds the input and output of this delay line. VTRs that record and play back SECAM video signals also use a comb-tooth filter that uses a 2H delay line to eliminate crosstalk.

On the other hand, in a VTR that records and plays back NTSC video signals, the A track records the chroma signal by inverting its phase every 1H, and the B track records the chroma signal as it is in continuous phase. The frequencies are interleaved with each other to separate the spectrum. And when playing,
A comb-tooth filter using a 1H delay line also eliminates crosstalk.

By the way, among television receivers for receiving PAL video signals, so-called dual TVs that can also receive NTSC signals are known. This receiver uses 4.43MHz for PAL as the color subcarrier frequency. Also
Also known is a so-called Trident TV that operates with color video signals of any of the PAL, NTSC, and SECAM systems.

A VTR that can use these dual TVs or Trident TVs as a monitoring device
When configuring a PAL or SECAM VTR as a basic component and a VTR that can at least play back NTSC signals as an additional function, a PAL or SECAM VTR is included in the playback system.
In addition to the comb-tooth filter using a 2H delay line for
It is necessary to provide a comb-tooth filter using a 1H delay line for NTSC, and a circuit system for switching these comb-tooth filters according to each playback mode is required, resulting in high cost.

The present invention was made in view of the above-mentioned problems, and uses a part of the 2H delay line of a comb tooth filter for PAL (or SECAM) to
It is designed to be used as a comb-tooth filter.

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

FIG. 1 is a block diagram of a chroma signal recording and reproducing system of a VTR to which the present invention is applied. This VTR is
It is configured to be able to record and reproduce PAL signals, NTSC signals, and SECAM signals, respectively. The symbol REC attached to the fixed contact terminal of each switch in Figure 1
indicates recording and PB indicates playback. Also
The switch, which has fixed contact terminals marked PAL, SECAM, and NTSC, can be switched according to the recording/playback mode of each video signal.

When recording a PAL signal, the PAL signal is supplied from terminal T1 to bandpass filter 1, where it is
The 4.43MHz band chroma signal is separated. The separated chroma signal is sent to the REC contact of switch 2,
It is supplied to the ACC circuit 3. The output of the ACC circuit 3 is supplied to the burst gate 8 through the REC contact of the switch 7, where the color burst signal is extracted. The burst signal is peak-detected by the burst detector 9, and depending on the detection output,
An ACC voltage is generated in an ACC voltage generator 10 . This ACC voltage is supplied to the ACC circuit 3,
Automatic correction of chroma level is performed.

The output of the burst gate 8 is connected to the switch 12
and 1H delay lines 14 and 15 (1H=1/f _HPAL : f _HPAL is PAL
a comb-tooth filter 16 (horizontal frequency of the signal);
supplied to Since the input and output of the 1H delay line 14 are added in the adder 17, a signal having a phase approximately in the middle of the PAL color burst signal whose phase varies by 90 degrees from line to line is obtained from the adder 17. The output of the adder 17 is supplied through a switch 18 to an injection oscillator 20 having a 4.43 MHz crystal oscillator 19, from which a 4.43 MHz color subcarrier f _SCPAL is obtained. Color subcarrier uses horizontal synchronization signal H
- Pseudo burst gate 2 that turns on every SYNC
2 is transformed into a pseudo burst signal and supplied to the adder 4 through the switch 23. accordingly
A pseudo burst signal is inserted into the horizontal synchronization signal section of the PAL chroma signal. The output of adder 4 is supplied to frequency converter 5.

In the frequency converter 5, the 4.43MHz band chroma signal is converted to a low frequency. Conversion carrier is AFC with variable frequency oscillator VCO24
formed by loops. That is, the output of the VCO 24 is divided into a horizontal frequency by a 4/175 frequency divider 25, and compared with the horizontal frequency f _HPAL =15.625 KHz of the recording PAL signal in a phase comparator 26. Since the comparison output is supplied to the VCO 24 through the low-pass filter 27 and the REC contact of the switch 28, the output frequency of the VCO 24 is fixed at (44-1/4)f _HPAL =683.59KHz. The output of the VCO 24 is supplied to a frequency converter 29, where the subcarrier f _SCPA of the output of the injection oscillator 20 is
_L (4.43MHz), so the output of the converter 29 becomes f _SCPAL + (44-1/4) f _HPAL .

The output of the frequency converter 29 is supplied to a phase shift circuit 32 through a phase inverter 30 which operates in NTSC mode. A shift signal is supplied to this phase shift circuit 32 from a control circuit 33 through a switch 34. This shift signal is formed based on the horizontal synchronization signal H-SYNC and the PG pulse indicating the rotational phase of the rotary head drum, and is a 1H cycle triangular wave as shown in FIG. The phase is shifted alternately by 1/8f _{H PAL} and 3/8f _HPAL for each field. As a result, from the output of the phase shift circuit 32, a converted carrier with a frequency represented by N tracks: f _SCPAL + (44-1/8) f _HPAL and N+1 track: f _SCPAL + (44 + 1/8) f _HPAL is obtained. .
Therefore, in frequency converter 5, 4.43MHz
The PAL chroma signal of the band is divided by field (44
-1/8) f _HPAL (=685.54KHz) and (44+1/8)
It is converted to the low frequency band of f _{HP AL} (=689.45KHz). The reduced chroma signal passes through a low pass filter 6, is added to the FM luminance signal, and is then recorded on a magnetic tape by a rotating video head. Therefore, between adjacent tracks, the chroma signals are mutually frequency interleaved and band separated.

Next, when reproducing a PAL signal, the reproduced signal is transferred from terminal T2 to low pass filter 36 and then to switch 2.
It is supplied to the ACC circuit 3 through the PB contact. ACC
The output of circuit 3 passes through adder 4 to frequency converter 5.
It is converted back to the 4.43MHz band at . The chroma signal returned to its original frequency is supplied to the comb filter 16 through the band pass filter 37 and the PB contact of the switch 13. Comb tooth filter 1
6, the signal delayed by 2H through the 1H delay lines 14 and 15 and the original signal are added in the adder 38, so that the filter 16 has a delay of 1/2f _HPAL as shown in FIG. 2A. It has a pass band. Therefore, (44+1/8)f _HPAL - (44-1/8)f _HPAL =1/4
The crosstalk component S from adjacent tracks having a frequency difference of _fHPAL is located in the valley of the comb characteristic and is therefore removed by the comb filter 16.

The output of the adder 38 (output of the comb filter 16) is led out to the terminal T3, mixed with the reproduced luminance signal as a reproduced PAL chroma signal PB-PAL, and then supplied to the reproduced monitor receiver. Note that the pseudo burst signal inserted during recording is extracted before being mixed with the luminance signal. The output of the comb tooth filter 16 is the PAL contact of switch 39 and the PB of switch 7.
It is also supplied to the burst gate 8 through the contact, where a pseudo burst signal is taken out. The pseudo burst signal is supplied to a phase comparator 40 forming an APC circuit. The output of the injection oscillator 20, which operates as a 4.43 MHz reference oscillator during reproduction, is applied to another input of the phase comparator 40. Therefore, an error output including jitter of the reproduced signal is obtained from the output of the phase comparator 40, and this output is supplied to an adder 43 through a low-pass filter 42.

In the adder 43, the output of the AFCID circuit 44, which operates when the VCO 24 mislocks, is added to the error output, and the added output is supplied to the VCO 24 as a control signal through the PB contact of the switch 28. Therefore, from the output of the VCO 24, an output having a frequency of approximately (44-1/4) f _HPAL, which follows the jitter of the reproduced chroma signal, is obtained. This output is added to the output (4.43 MHz) of the reference oscillator 20 in the frequency converter 29, and is further supplied to the phase shift circuit 32 to form the same converted carrier as during recording. Based on this conversion carrier, the reduced chroma signal is converted into the original PAL chroma signal with jitter suppressed in the frequency converter 5.

During playback, 4.43MHz reference oscillator 2 is used.
The zero output is supplied through the PAL contact of switch 45 to counter 46, where it is divided to an appropriate frequency and then supplied to the capstan servo circuit as a tape speed reference signal.

Next, a case will be described in which the VTR of this embodiment is used to reproduce a magnetic tape on which NTSC signals are recorded. However, as a playback monitor, PAL or
As an additional function of the SECAM system receiver, a so-called dual TV or Trident TV is used in which the subcarrier can receive PAL system NTSC signals. Therefore, the chroma center frequency of the reproduced NTSC signal is 4.43MHz, which is the same as that of PAL. In addition, so that the 1H delay line 14 or 15 of the comb-tooth filter 16 of the reproduction system can be used to configure a comb-tooth filter for the NTSC signal, the horizontal period or vertical period of the reproduced NTSC signal is not that of the original NTSC.
It is set to PAL (CCIR). For this reason
The capstan servo system used when reproducing NTSC signals is not the same as the servo system used when reproducing normal NTSC signals.The PAL horizontal frequency f _HPAL = 15.625KHz can now be obtained by changing the tape speed. There is.

Note that on a tape on which an NTSC signal is recorded, spectrum separation recording is performed so that the reduced converted chroma signals are interleaved between adjacent tracks with a frequency difference of 1/2f _HNTSC . That is, N
In the track, the chroma signal is recorded in continuous phase,
Furthermore, on the N+1 track, the chroma signal is recorded with its phase inverted every 1H.

In FIG. 1, the reproduced NTSC signal is supplied to the frequency converter 5 through the low-pass filter 36, the PB contact of the switch 2, the ACC circuit 3, and the adder 4. This converter 5 converts the input low-frequency chroma signal into a chroma signal in the f _SCPAL (4.43 MHz) band. The output of the frequency converter 5 is supplied to the 1H delay line 14 through the bandpass filter 37 and the PB contact of the switch 13. Since the input and output of this delay line 14 are added by an adder 17, the delay line 14
and adder 17, f _HP as shown in FIG. 2B.
An NTSC comb filter 47 having a pass band for each _AL is configured.

In the comb filter 47, crosstalk components from adjacent tracks having a frequency difference of 1/2 f _{H PAL} from the main signal are removed. The output of the adder 17 (the output of the comb filter 47) is led out from the terminal T5 as a reproduced NTSC signal PB-NTSC, and is also sent to the burst gate 8 through the NTSC contact of the switch 39 and the PB contact of the switch 7. The burst signal is extracted here. The output of gate 8 is fed to a phase comparator 40 of the APC circuit. In this comparator 40, the phases of the 4.43MHz reference signal from the reference oscillator 20 and the burst signal are compared, and the comparison output is output from the low-pass filter 42, adder 43, and switch 28.
It is supplied to VCO24 through the PB contact. As a result, the output frequency of the VCO 24 is controlled to be (44-1/4)f _HPAL in accordance with the reproduction frequency.

The output of the VCO 24 is frequency-converted by a frequency converter 29 to f _SCPAL + (44-1/4) f _HPAL and then supplied to a phase inverter 30 . This phase inverter 30 is connected via switches 48 and 49, respectively.
A PG pulse and a horizontal synchronizing signal H-SYNC are supplied, and based on these signals, a frequency interleaved conversion carrier is formed for each field, similar to that used during recording. That is, from the output of the phase inverter 30, N tracks: f _SCPAL + (44-1/4) f _HPAL N+1 tracks: [f _SCPAL + (44-1/4) f _{HPA L} ] ^-1 Carrier is obtained. however,
[ ] ^-1 indicates that the carrier is reversed every 1H. This conversion carrier is supplied to the frequency converter 5, so that the reproduced reduced chroma signal is correctly f
_SCPAL = Converted to a 4.43MHz band chroma signal.

In the system shown in Figure 1, if the tape speed is the same during playback of an NTSC tape as during recording,
The horizontal frequency is f _HNTSC = 15.734KHz, so 1H period is 1/f _HNTSC . However, since the delay amount of the 1H delay line of the comb filter 16 is set to 1/f _HPAL when the subcarrier is set to 4.43MHz, the horizontal period of the reproduced signal is 1/f _HNTS.
C is not equal to the 1H delay amount in the delay line 14. For this reason, as shown in FIG. 2B, the sideband J of the chroma signal whose spectrum is separated by f _SCPAL +nf _HNTSC is out of the pass band of the comb filter 47, making it impossible to perform good separation. Further, since the position of the crosstalk component is also outside the valley of the filter characteristic, the crosstalk component may remain in the filter output without being removed.

Therefore, in this embodiment, the tape speed is changed so that the horizontal frequency of the NTSC reproduction signal becomes f _HPAL =15.625 KHz. That is, in order for f _HPAL to be played correctly, the tape speed should be f _HPAL / f _HNTSC ≒ 15.625/15.73.
All you need to do is change it by 4≒0.993=99.3%. For this reason, the output of the reference oscillator 50 is switched by the switch 45 and used as the reference signal for the capstan servo system. The frequency division ratio of the counter 46 is 3.58NHz of a known NTSC VTR.
If the division ratio is the same as that of a capstan servo system using a reference oscillator (subcarrier), the crystal oscillator 51 of the reference oscillator 50 should be 3.579545×15.625/15.734≒3.5547 (MH
z), the tape speed is changed so that the playback horizontal frequency becomes _fHPAL . Note that without using the reference oscillator 50,
The frequency division ratio of the counter 46 that divides the output of the 4.43 MHz reference oscillator 20 may be changed during NTSC reproduction.

In FIG. 1, when recording and reproducing the SECAM signal, the voltage of the fixed bias source 52 is applied to the SECAM signal of the switch 28 as a control input of the VCO 24.
Supplied via contacts. Furthermore, the reproduced chroma signal is directly led out to the terminal T4 without passing through the comb filter 16.

Next, FIG. 3 is a partial block diagram of a chroma reproduction system showing another embodiment of the present invention. In this embodiment, a normal NTSC receiver can be used as a monitor receiver when playing back an NTSC tape. Therefore, the subcarrier frequency of the reproduced signal is f _SC =3.58MHz, and the tape speed is also
It is that of NTSC, and the horizontal frequency is also f _HNTSC =
It is 15.734KHz.

In Figure 3, when reproducing a PAL signal, the low frequency chroma signal is transmitted to terminal T2, similar to Figure 1.
The signal passes through the ACC circuit 3, is converted into the original chroma signal by the frequency converter 5, and then is supplied to the 2H comb-tooth filter 16 through the bandpass filter 37. The comb filter 16 has delay amounts of τ1 and τ1, respectively.
The chroma signal is composed of delay lines 14 and 15 of τ2 and an adder 38, and the chroma signal from which the crosstalk component of the output of the adder 38 has been removed is led out from the terminal T6 via the PAL contact of the switch 53.

The delay times of the delay lines 14 and 15 are set to τ1+τ2=2/f _HPAL , and so that the delay line 14 can be used as a comb filter during NTSC playback, τ1=
1/f _HNTSC . Therefore, τ2 is τ2=2/f _HPAL -1/f _HNTSC .

The output of the comb filter 16 is also supplied to a burst gate, and the pseudo burst signal separated here is supplied to a phase comparator 40. Phase comparator 4
0, the output of the reference oscillator 55 equipped with a 4.43MHz crystal oscillator 54 is output to the PAL of the switch 60.
It is supplied as a reference signal through a contact. Since the VCO 56 is also controlled by the output of the phase comparator 40, a 4.43 MHz subcarrier with APC applied is obtained from the VCO 56 as a reproduced pseudo burst signal. This subcarrier is added to the adder 57
The output of the AFC circuit (not shown) is added to the output (44±1/8) f _HPAL at , and then supplied to the frequency converter 5 as a conversion carrier.

When reproducing NTSC signals, delay line 14
(τ1=1/f _HNTSC ) and the adder 17 constitute a comb-tooth filter, in which crosstalk is removed. Further, the phase comparator 40 of the APC circuit receives the output of a reference oscillator 59 equipped with a 3.58 MHz crystal oscillator 58 as a reference signal via a switch 60.
NTSC contacts. Note that the reference signal for the capstan servo system during NTSC reproduction may be a frequency-divided output of the reference oscillator 59.

Next, FIG. 4 shows yet another embodiment. In this embodiment, as in the second embodiment, an NTSC receiver can be used as a monitor.
The same comb filter 16 as shown in FIG. 1 is used, and the delay amounts of the delay lines 14 and 15 are each 1/f.
_HPAL . Therefore, the capstan servo system uses the 3.5547 MHz reference oscillator 50 shown in Figure 1 as the speed reference signal, and the reproduction horizontal frequency is f _HPAL =
It is 15.625KHz. Also, the delay line 14 and the adder 17
is supplied to a comb-tooth filter 47 consisting of
The center frequency of the NTSC reproduced chroma signal is f _SCPAL =
It is set to 4.43MHz. The output of the comb tooth filter 47 is supplied to a frequency converter 61 which uses the frequency f _SCPAL + f _SCNTSC as a conversion carrier, from which an NTSC chroma signal with a center frequency of f _SCNTSC = 3.58 MHz is obtained. The output of the converter 61 is passed through a bandpass filter 62 and output from terminal T7 to NTSC.
Supplied to the receiver.

As described above, the present invention includes a comb-tooth filter for crosstalk removal that includes two delay lines whose total delay amount is twice the horizontal scanning period of a PAL video signal.
When reproducing an NTSC signal, one of the delay lines was used to form a comb-tooth filter for removing crosstalk. Therefore, since a part of the comb-tooth filter for PAL is shared without using a separate delay line as the comb-tooth filter for NTSC, the configuration is simpler and the cost is lower.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a chroma signal recording and reproducing system of a VTR to which the present invention is applied, Fig. 2 is a spectrum diagram showing the passage characteristics of the comb filter shown in Fig. 1, and Fig. 3 is another embodiment of the present invention. FIG. 4 is a partial block diagram of a chroma regeneration system showing still another embodiment. In addition, in the symbols used in the drawings, 14, 15...delay line, 16, 47...comb tooth filter.

Claims (1)

[Claims] 1 Chroma signals are frequency interleaved between adjacent parallel tracks to generate an NTSC video signal or
In a video signal reproducing device that is configured to obtain a playback signal from any recording medium on which a PAL video signal is recorded, serial connections are made so that the total delay amount is twice the horizontal scanning period of the PAL video signal. When reproducing the NTSC video signal, the NTSC video signal is
The input and output of the first delay line constitute the comb filter, and when reproducing the PAL video signal, the input and output of the first delay line constitute the comb filter. A video signal reproducing device configured to include a comb-tooth filter to remove crosstalk from adjacent tracks. 2 Both the delay amounts of the first and second delay lines are
equal to the horizontal scanning period of the PAL video signal, and
2. The video signal reproducing device according to claim 1, wherein when reproducing an NTSC video signal, the running speed of the recording medium is changed so that the horizontal scanning period of the reproducing signal is approximately equal to the horizontal scanning period of the PAL video signal. 3. Claim 1 in which the delay amount of the first delay line is equal to the horizontal scanning period of the NTSC video signal.
2. Video signal reproducing device.