JPH0453378A - Time base collector - Google Patents

Abstract

PURPOSE:To attain accurate time axis correction with respect to a reproduced video signal even at special reproduction by generating a memory write clear pulse giving a write reference based on a reproduction horizontal synchronizing signal, a head switching pulse, a capstan motor drive pulse and a tape speed discrimination signal. CONSTITUTION:A switching pulse of heads 3, 4 is delayed for a proper horizontal period in response to the tape drive mode at the special reproduction in which a magnetic tape 7 is in standstill or intermittent drive, and a write clear pulse to a memory 12 generated from a reproduced vertical synchronizing signal is generated instead in the case of the normal reproduction. Thus, a memory clear pulse giving a write reference is generated based on the switching pulse of the heads 3, 4, a drive pulse of a capstan motor 6 and a tape speed discrimination signal. Thus, stable time axis correction is attained without relying on the reproduced vertical synchronizing signal whose reproduction is unclear.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a time base corrector that can operate reliably even during special playback where there is a concern about missing vertical synchronization signals.

[Prior Art] A home video tape recorder separates a video signal into a luminance signal and a chrominance signal, then mixes the FM-modulated luminance signal and the low-frequency-converted chrominance signal, and outputs the signal through a rotating magnetic spatula. It uses a method of recording on magnetic tape, and during playback, the signal is processed using a process that is exactly the opposite of that during recording.

However, during signal reproduction, there have been problems such as color lock being lost or images being distorted or curved due to fluctuations in the time axis such as uneven rotation of the rotating magnetic head and fluctuations in tape running speed. In particular, conventional home video tape recorders output playback video signals without any time axis fluctuation correction, so the amount of fluctuation, including slow drift components, can reach about 100 μs. Consideration began to be given to introducing a time base collector, which is commonly used in video tape recorders.

A conventional time base collector 1 shown in FIG. 8 is applied to a home video tape recorder, and includes a pair of rotating magnetic heads 3 that are rotationally driven by a drum motor 2.
．． 4 is a changeover switch 8 that alternately reads video signals from a magnetic tape 7 running under the rotational power of a capstan motor 6 monitored by a servo mechanism 5, and switches the read video signals by a head switching pulse.
The signal is sent to the reproduced signal processing circuit 9 via. The reproduced signal processing circuit 9 performs FM demodulation of the luminance signal, performs high frequency conversion of the low frequency converted color signal to the original signal band, mixes the obtained luminance signal and color signal, and sends the mixed signal to the first stage of the time base collector 1. It is sent to the provided AD converter 10.

The video signal converted into digital data by the AD converter 10 is written to a predetermined location in the memory 12 according to a write address specified by an address generator 11. −
The video data once written into the memory 12 is read out according to the read address specified by the address generator 11, and first, horizontal and vertical synchronization signals are added to it in the sync processor 13, and then the video data is input to the DA converter 14. It is converted into an analog video signal and sent to the outside. In this case, each horizontal and vertical signal added to the time-axis corrected video signal must be generated based on a reference signal that is completely separate from the horizontal and vertical synchronization signals that are reproduced along with the video signal. There is.

Here, a horizontal synchronization signal is generated by dividing the read clock outputted from the read clock generation circuit 15 with N times the horizontal frequency, and on the other hand, from the reference signal sent to the read clock generation circuit 15, a synchronization separation circuit The synchronization signal separated by 16 is supplied to a clear pulse generation circuit 17, and is used to generate a vertical period memory read clear pulse and a vertical synchronization signal.

On the other hand, regarding the write clock, the reproduction horizontal synchronization signal separated by the synchronization separation circuit 18 connected to the reproduction signal processing circuit 9 is multiplied by N in the write clock generation circuit 9 incorporated in the phase-logged loop. This is used as the sampling clock of the AD converter 10 and at the same time as the write clock. In addition, the writing clog is
1 at the 1/N frequency divider 20. After being frequency-divided by /N, the phase of the write clock is compared with the reproduced horizontal synchronizing signal in the phase comparator 21, and the frequency of the write clock is controlled so that the phase comparison error obtained at that time converges to zero. On the other hand, the memory write clear pulse is generated by a clear pulse generation circuit 22 connected to the synchronization separation circuit 16 based on the reproduced vertical synchronization signal.

[Problems to be Solved by the Invention] The conventional time base collector 1 described above is good during so-called normal playback, where the tape running mode is the same during signal recording and signal playback, but for example, when the magnetic tape 7 is kept stationary while rotating. When reproducing still images by rotating only the magnetic heads 3 and 4, the rotating magnetic heads 3 and 4 scan over the width of two tracks, as shown in FIG. The vertical synchronization signal that is used is likely to be lost. For this reason, during such special playback, it may not be possible to extract the vertical synchronization signal from the reproduced video signal, and in such cases, a memory write clear pulse cannot be generated, resulting in the problem that time axis correction is often impossible. In addition, when reproducing still images, as shown in FIG. 10, it is necessary to perform alternate reproduction using the rotating magnetic heads 23 and 24 for special reproduction, which have the same azimuth as the rotating magnetic heads 3 and 4 for normal reproduction. A special reproduction rotary magnetic head 24, which is disposed close to a normal reproduction rotary magnetic head 4 which is not used for reproduction, is disposed at a position offset from the rotary magnetic head 4 by, for example, two horizontal periods (2H) in time. Therefore, there was a problem in that the memory write clear pulse could not simply be replaced with a head switching pulse.

[Means for Solving the Problems] This invention solves the above problems, and it is possible to transfer video signals alternately reproduced from a magnetic tape by a pair of rotating magnetic heads to a memory whose write operation is cleared in vertical cycles. This is a time base collector that corrects the time axis by reading according to a reference clock independent of writing and writing operations. During normal playback, it generates a memory write clear pulse from the playback vertical synchronization signal and drives the magnetic tape statically or intermittently. The present invention is characterized by comprising a memory write clear pulse generating means which delays the head switching pulse by an appropriate horizontal period according to the tape running mode and generates a memory write clear pulse as a substitute during special playback.

[Function] This invention delays the head switching pulse by an appropriate horizontal period depending on the tape running mode during special playback performed by stationary or intermittent driving of the magnetic tape, and generates it from the playback vertical synchronization signal during normal playback. By generating the memory write clear pulse as a substitute, the memory clear pulse that provides the write reference can be generated based on the horizontal synchronization signal, the head switching pulse, the capstan motor drive pulse, and the tape speed determination signal. Enables stable time axis correction without relying on the reliable playback vertical synchronization signal.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 is a circuit configuration diagram showing one embodiment of the time base collector of the present invention, FIG. 2 is a circuit diagram of the main part of FIG. 1, and FIG. 3 is a phase shift circuit shown in FIG. 2. The signal waveform diagrams of each part, Figures 4 to 7, are the shift l shown in Figure 3 in standard still image playback mode, standard intermittent slow playback mode, 3x still image playback mode, and 3x intermittent slow playback mode, respectively. FIG. 2 is a signal waveform diagram of each part of the -ffi setting circuit.

The time base corrector 31 shown in FIG. 1 is capable of performing accurate time axis correction on the reproduced video signal not only during normal playback but also during special playback.
By generating the memory write clear pulse, which is the writing reference for the playback video signal, based on the playback horizontal synchronization signal, head switching pulse, capstan motor drive pulse, and tape speed determination signal, instead of the playback vertical synchronization signal, playback This is to appropriately deal with special playback in which the vertical synchronization signal is missing.

By the way, in special playback, it is necessary to adjust the phase of the memory write clear pulse appropriately according to the rotating magnetic head 3, 4 or 23, 24 to be used for playback and the tape running state. That is, when reproducing still images by rotating only the rotary magnetic heads 3, 4, 23, 24 while the magnetic tape 7 is stopped, the normal reproduction heads 3, 4
It goes without saying that the installation of the special playback heads 23 and 24 requires a correction of 2H depending on the position.

Furthermore, during intermittent slow playback in which the magnetic tape 7 is intermittently advanced, normal playback is performed while the tape is running, and still image playback is performed while the tape is stopped, the magnetic tape 7 may be running or stopped. It is necessary to perform phase correction depending on the situation, such as whether the magnetic tape 7 is recording in the standard mode or the triple mode.

Here, we will first explain the generation process of the three types of delayed pulses that are not written to when generating the memory write clear pulse.
FIGS. 2 and 3 will be explained together.

The three types of delayed pulses are pulses that are generated with a shift of one horizontal period based on the rise or fall of the pulse obtained by phase modulating the head switching pulse, and here, the OH delay pulse, We will call them LH delayed pulse and 2H delayed pulse to distinguish them. The head switching pulse output from the servo mechanism 5 is phase-modulated by the phase modulator 32, and then sent from the 1/N frequency divider 20 in the phase-locked loop that generates a pulse phase-locked to the reproduced horizontal synchronization signal. A phase comparator 33 compares the phase with the supplied horizontal synchronizing pulse. Then, the phase comparison error at this time is integrated by an integrator 34, and is used as a modulation input of a phase modulator 32 via a subsequent amplifier circuit 35. Therefore, the head switching pulse is phase-modulated so that it rises in synchronization with the falling edge of the horizontal synchronization pulse, which is phase-locked by the phase-locked loop.

As a result, the head switching pulse and the reproduced horizontal synchronizing signal are aligned in phase, and preparations for generating the three types of delay pulses are completed.

The phase shift circuit 36 has two D flip-flop circuits 37 that latch two phase-modulated head switching pulses using the reproduced horizontal synchronization signal fh as an operation clock.
．． 38, and five D flip-flop circuits 39, 4.04, 1.4.2. which operate using the double frequency signal 2fh of the reproduced horizontal synchronization signal fh as the operating clock. 43, an exclusive OR gate circuit 44 whose inputs are the outputs of the D flip-flop circuits 37 and 38, and an output of the exclusive OR gate circuit 44 and the D flip-flop circuit 4.
It consists of an AND gate circuit 46 to which the polarity inverted output of 3 is input, two changeover switches 47 and 48, and the like. The changeover switch 47 outputs either the O H delay pulse that is the output of the AND gate circuit 40 or the output of the changeover switch 48 in the previous stage, and the changeover switch 48 outputs the output of four D Switch output between the 1H delayed pulse, which has undergone a signal delay of LH by two of the flip-flop circuits 39 to 42, or the 2H delayed pulse, which has undergone a signal delay of 2H by all four flip-flop circuits. do.

As is clear from the signal waveform diagram shown in FIG. 3, the outputs of the two D flip-flop circuits 37 and 38 subjected to exclusive OR by the exclusive OR gate circuit 44 are shown in FIG. The signal shown is sent to a D flip-flop circuit 45 and an AND gate circuit 46, and an OH delay pulse is obtained as an AND output of the AND gate circuit 46. Note that the OH delay pulse has a delay of about 015H with respect to the phase-modulated head switching pulse, but the time when the delay pulse is delayed by 0.5H is treated as zero phase.

By the way, the three types of delay pulses generated within the phase shift circuit 36 are selected through the control of the changeover switches 47 and 48 by the shift amount setting circuit 49, and are sent to the clear pulse generation circuit 22 as memory write clear pulses. The shift amount setting circuit 49 converts the capstan motor drive pulse and the tape travel discrimination signal sent from the servo mechanism 5 into two OR gate circuits 50°5.
1 and the exclusive or game 1 circuit 52 and the D flip-flop circuit 53 perform logic processing to generate two types of switching control pulses 3 for the switching switches 48 and 47.
Generate 1.82. Here, the capstan motor drive pulse, which takes a high level while the capstan motor is activated, is input to one of the two OR gate circuits 50 and 51, and is input to the D flip-flop circuit 37 in the phase shift circuit 36. The output is inverted and inputted to one OR gate circuit 50, and inputted as is to the other OR gate circuit 51. Furthermore, the tape running mode determination signal, which is at a low level when recording in the standard mode and takes a high level when recorded in the 3x mode, is connected to the output of the OR gate circuit 51 and the input of the exclusive OR gate circuit 52. The output of this exclusive-OR gate circuit 52 becomes a switching control pulse S2 for the switching switch 47. On the other hand, the OR gate circuit 5
The output of the D flip-flop circuit 53, which latches the output of 0 at the trailing edge of the memory write clear pulse, becomes the switching control pulse S1 for the switching switch 48.

First, when playing still images from the magnetic tape 7 recorded in the standard mode, the rotating magnetic head 3 (4) and the special playback rotating magnetic head 23 (24) having the same azimuth are alternately switched. Therefore, when one rotary magnetic head 3 (4) which is also used for special reproduction is used as a reference, the special reproduction rotary magnetic head 23 (2/1.)
The video signal read by the head switching pulse is delayed by exactly 2H from the head switching pulse as described above. Therefore, as shown in Fig. 4, the switching control pulse S1 is always at a high level, whereas the switching control pulse S2 switches following the head switching pulse, as shown in Fig. 4 (K). Thus, the memory write clear pulse is a pulse train in which 2H delay pulses and OH delay pulses appear alternately. Therefore, the time base corrector 31 can accurately apply time axis correction to the reproduction output of the special reproduction rotary magnetic head 23 (24).

On the other hand, when playing back the magnetic tape 7 recorded in standard mode by intermittently repeating still image playback (so-called intermittent slow playback), during the period when the tape running is stopped, the still image playback is This is the same as , but the mode is normal playback while the tape is running. For this reason, as shown in FIG. 5, a 2H delay pulse is used during the drive period of the capstan motor 6, and an IH delay pulse is used immediately after the drive is stopped. This is because during the transition period until the running magnetic tape 7 stops, it can be considered to be in an intermediate mode between normal playback and still image playback, and this is fully supported by experimental results. This is where I am. In addition, since the IH delay pulse in this case can be considered as a modified 2H delay pulse, it is appropriate to start with the OH delay pulse when transitioning to still image playback, and after the capstan motor 6 has stopped. With the OH delay pulse at the beginning, the 2H delay pulse and the OH delay pulse appear alternately.

Note that, as in the case of still image playback described above, since the tape running mode discrimination signal is at a low level indicating recording in the standard mode, the output of the OR gate circuit 5 in the shift amount setting circuit 49 is directly transmitted to the exclusive OR gate circuit. 5
Pass 2.

Next, when playing back still images from the magnetic tape 7 recorded in the 3x mode, the difference in this case from playing back still images from the magnetic tape recorded in the standard mode is that the tape running mode determination signal is only the polarity of Therefore, the only major difference is that the exclusive OR gate circuit 52 in the shift amount setting circuit 49 operates as a polarity inversion circuit, but as shown in FIG. 6(K), the O H delay pulse with respect to the head switching pulse is It should be noted that the order in which the 2H delayed pulses are generated is reversed from that shown in FIG.

Finally, in the case of intermittent slow playback of the magnetic tape 7 recorded in the 3x mode, in this case, as shown in FIG. 7, drive pulses are output to the capstan motor 6. During this period, the 2H delay pulse will not be output.
Outputs only OH delayed pulses. During the transition period when the running magnetic tape 7 comes to a stop, it is considered to be an intermediate mode between tape running and tape stopping, as in the case of intermittent slow playback of a magnetic tape recorded in the standard mode described above. Instead, it is determined that the magnetic tape 7 is stopped, and the OH delay pulse is selected.

In this way, the time base collector 31 can generate a memory write clear pulse that provides a write reference based on the reproduction horizontal synchronization signal, the head switching pulse, the capstan motor drive pulse, and the tape speed discrimination signal, For example, in order to use rotating magnetic heads 3 and 23 or 4 and 24 having the same azimuth, such as still image reproduction, a special reproduction rotating magnetic head is adopted in place of the rotating magnetic head 3 or 4 used for normal reproduction. head 2
3 or 24, even if the assembly on the head drum causes a problem of phase shift caused by positional shift, by adding phase correction to the head switching pulse, an appropriate memory write clear pulse can be generated. Also, unlike still image playback, even in intermittent slow playback where the tape runs and stops repeatedly, the transient timing shift caused by tape forwarding can be corrected by taking into account the tape running state in addition to the correction amount. By adding this, it is possible to deal with it realistically, and as a result, the time axis correction, which was conventionally taken only for normal playback where the tape running mode during recording and playback is the same, is changed to intermittent slow speed correction for still image playback. It can also be effectively applied during special playback such as playback.

[Effects of the Invention] As explained above, the present invention delays the head switching pulse by an appropriate horizontal period depending on the tape running mode during special playback performed by stationary or intermittently driving the magnetic tape, and performs normal playback. If there is a memory write clear pulse generated from the playback vertical synchronization signal, it is generated as a substitute, so the memory write clear pulse that provides the write reference is used as a substitute for the playback horizontal synchronization signal, the head switching pulse, the capstan motor drive pulse, and the tape speed. A rotating magnetic head for special reproduction that can be generated based on a discrimination signal and is adopted instead of a rotating magnetic head used for normal reproduction in order to use a rotating magnetic head with the same azimuth, for example, for still image reproduction. When the magnetic head is assembled on the head drum, phase correction is applied to the head switching pulse even when the phase shift with respect to the rotating magnetic head for both normal playback and special playback, which occurs due to misalignment, is a problem. By doing this, it is possible to generate an appropriate memory write clear pulse, and even in intermittent slow playback where the tape runs and stops repeatedly, unlike still image playback, the transient timing shift caused by tape advance can be compensated for by the amount of correction. This can be done realistically by making some modifications that take into account the tape running conditions, and this allows the time axis to be changed, which was previously only used for normal playback where the tape running mode during recording and playback is the same. The correction has excellent effects such as still image regeneration and can be effectively applied even during special playback such as intermittent slow playback.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the time base collector of the present invention, FIG. 2 is a circuit diagram of the main part of FIG. 1,
Figure 3 is a signal waveform diagram of each part of the phase shift circuit shown in Figure 2, and Figures 4 to 7 are standard still image playback mode, standard intermittent slow playback mode, 1x still image playback mode, and 3x still image playback mode, respectively. The signal waveform diagram of each part of the shift amount setting circuit shown in FIG. 3 in the 3x intermittent slow playback mode, and FIG. 8 are as follows:
A circuit diagram showing an example of a conventional time base collector,
FIG. 9 is a diagram showing a trace pattern of the rotating magnetic field during still image reproduction, and FIG. 10 is a diagram showing the head arrangement of the rotating magnetic head shown in FIG. 8. 3.4, 23, 24. ,,rotating magnetic head,506. Servo mechanism, 12. ,,Memory,18. . , synchronous separation circuit, 22. ,, Clear pulse generation circuit, 3
1. , , Time base collector, 32. . , phase modulator, 36. ,, phase shift circuit, 4900.
Shift amount setting circuit.

Claims (1)

[Claims] A time base collector that corrects the time axis by writing video signals alternately reproduced from a magnetic tape by a pair of rotating magnetic heads into a memory whose writing operations are cleared in vertical cycles, and reading them out according to a reference clock that is independent of the writing operations. During normal playback, a memory write clear pulse is generated from the playback vertical synchronization signal, and during special playback, which is performed by statically or intermittently driving the magnetic tape, a head switching pulse is generated for an appropriate horizontal period according to the tape running mode. A time base collector comprising memory write clear pulse generating means for generating a delayed memory write clear pulse instead.