Reproducing Apparatus With Time Base Corrector

1. Field of the Invention

This invention relates to a signal reproducing apparatus and more particularly to a signal reproducing apparatus which is provided with a circuit for correcting the time base of a reproduced signal.

2. Description of the Related Art

In the conventional signal reproducing apparatus of the above stated kind, such as a video tape recorder (hereinafter referred to as VTR) of the known low band converting type, a time base correction circuit (or a time base corrector, hereinafter referred to as TBC) has been arranged to give a time base corrected carrier chrominance signal by stepping up a horizontal synchronizing signal which is extracted from a reproduced video signal by means of a PLL circuit to a low-band converted carrier chrominance signal frequency; and by frequency converting a low-band converted carrier chrominance signal with a signal obtained by frequency converting a signal produced from a voltage controlled oscillator (hereinafter referred to as VCO) which is controlled on the basis of the stepped up horizontal synchronizing signal and a phase difference between the output of a reference oscillator and a reproduced color burst signal.

In addition to correcting the time base of the carrier chrominance signal, there has been contrived a method for correcting, at the same time, the time base of a luminance signal. In accordance with this method, the reproduced video signal is supplied to a variable delay line consisting of a CCD delay line; time base variations are extracted by using the above stated horizontal synchronizing signal; and the delay time obtainable by the variable delay line is controlled for correcting the time base of the luminance signal.

The above stated TBC of the conventional VTR has presented the following problem. In shifting from one to another the so-called normal reproduction mode and a special reproduction mode such as a high speed search mode or a slow reproduction mode, the synchronizing signal extracted from the reproduced video signal is apt to be disturbed by the dislocated servo lock of frequency and phase of the rotation of a drum and a capstan. The TBC malfunctions when the frequency and phase deviations come to exceed the correctable range of the TBC. The malfunction has disturbed a picture thus reproduced. To prevent such disturbance of the reproduced picture, varied methods have been developed including among others. A method of not allowing the TBC to operate in the special reproduction modes. Another method wherein a signal indicative of each special reproduction mode is produced; and after change-over to a special reproduction mode, the TBC is kept inoperative during a period of time set for the mode indicated by the signal.

The former method, however, prohibits the use of the TBC for special reproduction. Meanwhile, the latter makes the arrangement of the apparatus more complex accordingly as the number of special reproduction modes increases. Besides, it is difficult to set the periods of time during which the TBC must be kept inoperative.

Further, there are occurrences of some time base variations that are hardly pursuable by the TBC due to some reason other than the special reproduction. In such a case, the conventional time base correction circuit rather has brought about some adverse effect on reproduced signals.

In view of the above stated problems of the prior art, it is an object of this invention to provide a reproducing apparatus which is capable of adequately performing the time base correction under any conditions.

It is another object of the invention to provide a reproducing apparatus which is capable of performing the time base correction during the special reproduction.

Under these objects, a signal reproducing apparatus arranged according to this invention as an embodiment thereof comprises: reproducing means for reproducing a recorded signal by tracing a record bearing medium; time base correction means for correcting the time base of the signal reproduced by the reproducing means; transportation means for transporting the record bearing medium; and switch-over means for changing over a transportation speed of said record bearing medium transported by said transportation means and for changing over a response speed of the time base correction means according to the changeover of the transportation speed.

It is a further object of the invention to prevent a reproduced signal from being deteriorated by any faulty action of a time base correction circuit.

Under that object, a signal reproducing apparatus arranged according to the invention as another embodiment thereof comprises: reproducing means for reproducing a recorded signal by tracing a record bearing medium; time base correction means for correcting the time base of the signal reproduced by the reproducing means; moving means for moving the record bearing medium and the reproducing means relative to each other; control means arranged to act on the moving means for controlling the relative movement of the record bearing medium and the reproducing means to be in a predetermined steady state; detecting means for detecting that the relative movement of the record bearing medium and the reproducing means is brought into the steady state by the control means; and switch-over means for changing over an acting state of the time base correction means according to an output of the detecting means. The above and other objects and features of the invention will become apparent from the following detailed description of embodiments thereof taken in connection with the accompanying drawings.

FIG. 1 is a block diagram showing in outline the essential parts of a VTR arranged as an embodiment of this invention.

FIG. 2 is a block diagram showing in outline the essential parts of a VTR arranged as another embodiment of this invention.

This invention is applied to VTRs in the cases of embodiments described below.

FIG. 1 is a block diagram showing in outline the essential parts of a VTR which is arranged according to this invention as an embodiment thereof. Referring to FIG. 1, a charge coupled device (CCD) 1 is employed as a variable delay element. A recorded video signal is reproduced from a magnetic tape T by means of a rotary head H and is supplied to the CCD 1. A synchronizing signal separation circuit 2 is arranged to separate a horizontal synchronizing signal from the video signal produced from the CCD 1. A phase comparator 3 is arranged to have its output supplied via a low-pass filter (LPF) 4 to a voltage controlled oscillator (hereinafter referred to as VCO) 5. The phase comparator 3 compares the phase of the reproduced horizontal synchronizing signal separated by the synchronizing signal separation circuit 2 with the oscillation frequency of the VCO 5. The output of the phase comparator 3 is also supplied to another VCO 7 via an equalizer 6. The frequency of the VCO 7 is used as a clock signal for the above stated CCD 1. A phase locked loop (hereinafter referred to as PLL) is formed jointly by the phase comparator 3, the LPF 4 and the VCO 5. The VTR has varied operation modes including a normal reproduction mode, a still picture reproduction mode, a slow motion reproduction mode, a high speed search reproduction mode, etc. A system controller 8 is arranged to control change-over from one mode to another among these varied modes. A capstan 9 is arranged to transport the magnetic tape T at a speed determined for each of these modes designated by the system controller 8. A reproduced signal processing circuit 10 is arranged to perform a known signal processing action on the video signal which has been time base corrected by the CCD 1. An output terminal 11 is arranged to produce the video signal processed by the circuit 10.

In the normal reproduction mode, the capstan 9 is caused to transport the magnetic tape T at the same speed as a speed at which recording has been performed. The synchronizing signal separation circuit 2 extracts the horizontal synchronizing signal from the reproduced video signal after the signal has passed through the CCD 1. The extracted horizontal synchronizing signal is supplied to one of the input terminals of the phase comparator 3. The output of the phase comparator 3 causes through the LPF 4 the input voltage of the VCO 5 to vary. Then, the oscillation frequency of the VCO 5 varies accordingly. The oscillation output of the VCO 5 is phase compared with the reproduced horizontal synchronizing signal by the phase comparator 3. As a result of the phase comparison, a time base error signal is produced from the phase comparator 3. The time base error signal is supplied to the equalizer 6, which performs phase compensation. Then, the phase compensated time base error signal produced from the equalizer 6 is supplied to the VCO 7. This causes the oscillation frequency of the VCO 7. The VCO 7 then produces an output, which is applied to the CCD 1 as a clock signal. The time base of the reproduced video signal is changed as necessary by varying the delay time of the CCD 1 with the CCD 1 thus being driven by the clock signal.

In the case of high speed search reproduction mode which is one of the special reproduction modes and is performed, for example, to look up a part of the record, the system controller 8 causes the capstan 9 to transport the tape T at a high speed. The system controller 8 then also produces a signal S indicative of the search being conducted. While the search signal S is being produced, the response speed of the VCO 5 is changed by changing the time constant (or gain) of the LPF 4. By this, in the high speed search mode, a time base error signal is produced from the phase comparator 3 to change the response speed of the whole VTR. The time base correction is thus carried out, in the high speed search mode, in the same manner as in the normal reproduction mode.

Further, while the time constant (or gain) of the LPF 4 is arranged to be changed in the special reproduction mode in the case of this embodiment, this arrangement may be changed to make adjustment, for example, by using the equalizer 6, instead of the LPF 4. In that instance, the frequency of the VCO 7 is changed by changing the output voltage of the equalizer 6. Either of these different arrangements may be selected according to circumstances. While the high speed search reproduction is taken up by way of example in the above description, this invention is advantageously applicable also to other special reproduction modes such as the slow reproduction mode, the still picture reproduction mode, etc. In the case of slow reproduction or still reproduction, for example, the time constant or the LPF 4 or the characteristic of the equalizer 6 is changed to adjust the response characteristic of the time base correction circuit, so that the time base correction can be adequately accomplished at a response speed which is most apposite to any of the modes selected. In this instance, the system controller 8 produces the signal S according to the mode selected.

As described in the foregoing, the rotary head type reproducing apparatus according to the invention is capable of adequately performing the time base correction in any of the different operation modes by virtue of a slight addition to the circuit arrangement of the TBC circuit provided for normal reproduction.

FIG. 2 shows in outline the essential parts of a VTR arranged according to this invention as another embodiment thereof. In FIG. 2, the same components as those of the embodiment shown in FIG. 1 are indicated by the same reference numerals. The illustration includes a magnetic tape T; a rotary drum 20 which is wound around more than 180 degrees by the magnetic tape T; rotary magnetic heads Ha and Hb which are mounted on the rotary drum 20 at a phase difference of at least 180 degrees between them; and a switch 12 which is arranged to alternately produce signals reproduced by these heads Ha and Hb. A sample-and-hold (hereinafter referred to as S/H) circuit 33 is arranged to operate using a horizontal synchronizing signal which is extracted by the synchronizing signal separation circuit 2 as sampling pulses. The output of the S/H circuit 33 is arranged to be supplied via the LPF (low-pass filter) 4 to the VCO 5. The output of the VCO 5 is arranged to be transformed into a trapezoidal wave by a trapezoidal wave generator 36. The trapezoidal wave thus obtained is supplied to the S/H circuit 33. The S/H circuit 33, the LPF 4, the VCO 5 and the trapezoidal wave generator 36 jointly form a PLL circuit. The output of the S/H circuit 33 is also supplied via a switch 19 and the equalizer 6 to the VCO 7 to vary thereby the oscillation frequency of the VCO 7. The output of the VCO 7 is arranged to be used as a clock signal for driving the CCD 1.

The reproduced video signal which is produced from the CCD 1 is supplied to the reproduced signal processing circuit 10. The circuit 10 then performs a known signal processing action. The signal thus processed is supplied via the output terminal 11 to an applicable device such as an image receiver.

The servo circuit of the embodiment operates in the following manner: The reproduced signal from the switch 12 is supplied to a tracking control signal generating circuit 13 (hereinafter referred to as ATF circuit) which is arranged to operate in accordance with the known four-frequency method. The ATF circuit 13 then produces a tracking error signal (hereinafter referred to as ATF signal) which is obtained by performing a known process on reproduced pilot signals. In the normal reproduction mode, this ATF signal is supplied to a capstan control circuit 14 as a tracking control signal. The rotation of the capstan 15 is then controlled in such a manner that the heads Ha and Hb trace one by one recording tracks formed on the tape T in the so-called just-track state in which the middle part of each of the heads Ha and Hb coincides with the center line of each applicable track. In case that the system controller (which is not shown) produces an instruction for special reproduction, such as slow reproduction, high speed search reproduction, or some other special reproduction, the ATF circuit 13 samples and holds the ATF signal at an applicable predetermined timing before supplying it to the capstan control circuit 14 as the tracking control signal. The sample-and-holding timing is determined in such a way as to obtain the above stated just-track state. For example, in the case of the high speed search reproduction mode, the heads Ha and Hb are caused to be at a predetermined rotation phase.

A stable servo state can be considered to have been attained if the absolute value of the level of the tracking control signal is low, irrespective as to whether the VTR is in the normal reproduction mode or in a special reproduction mode. A capstan phase lock detecting circuit 16 is arranged to produce its output at a high level when the capstan control system is in a stable state (or a servo lock state) as judged from the level of the tracking control signal.

Meanwhile, a phase detector 21 is arranged to detect the rotation phase of the drum 20 and to produce pulses. The pulse output of the phase detector 21 is phase compared by a phase comparator 23 with the signal output of a reference oscillator 22 which is arranged to oscillate at a frequency corresponding to a desired rotational frequency. The signal output of the phase comparator 23 is supplied to a drum control circuit 24 as a drum rotation phase control signal. The drum 20 is controlled to rotate at a given phase in accordance with this rotation phase control signal. A servo for the phase of the drum 20 can be considered to be in a stable state if this rotation phase control signal is at a low level. This is arranged to be detected by a drum phase lock detector 25. The detector 25 is arranged to produce its output at a high level when the phase servo of the rotary drum is in a stable state (a servo lock state).

Further, the description given hereinafter is on the assumption that the rotating speed of the drum 20 and that of the capstan 15 are also in servo lock states when the rotation phase of the drum 20 and that of the capstan 15 are in their servo lock states.

In the circuit of FIG. 2, when the frequency and the phase of the drum 20 and those of the capstan 15 are both in locked states during normal reproduction, the horizontal synchronizing signal is extracted by the synchronizing signal separation circuit 2 from the reproduced video signal which has passed the CCD 1. The horizontal synchronizing signal thus extracted is produced in the form of sampling pulses. This pulse output of the circuit 2 is supplied to the S/H circuit 33. However, since the S/H circuit 33 forms the PLL circuit in conjunction with the LPF 4, the VCO 5 and the trapezoidal wave generator 36, the output of the S/H circuit 33 is used as a time base error portion of the reproduced signal. The output of the S/H circuit 33 is supplied via the switch 19 to the equalizer 6 to be phase compensated by the equalizer 6. The output of the S/H circuit 33 which is thus phase compensated is supplied to the VCO 7 to change thereby the oscillation frequency of the VCO 7. The output of the VCO 7 is used as a clock signal for driving the CCD 1. The CCD 1 is thus driven to correct the time base variations of the reproduced video signal.

In the event of special reproduction, when the phase servo of one of or those of both of the drum and capstan are not in the servo lock state, a NAND gate 30 turns on. The signal output of the NAND gate 30 causes the synchronizing signal separation circuit 2 to stop operating. As a result, the sample pulses from the S/H circuit 33 ceases. Further, the output of the S/H circuit 33 is fixed at such a given voltage that causes the VCO 5 to oscillate at the frequency of the horizontal synchronizing signal. Further, the output of the NAND gate 30 shifts the position of the switch 19 to a terminal on a fixed or constant voltage side thereof (on one side H thereof). The fixed constant voltage is supplied via the equalizer 6 to the VCO 7. This makes the input voltage of the VCO 7 unvarying. Accordingly, the frequency of the clock signal applied to the CCD 1 also becomes unvarying. The time base correcting action then comes to a stop.

With the embodiment arranged as described in the foregoing, in the event of occurrence of a large tracking error at the time of change-over between normal reproduction and special reproduction, the level of the output of the capstan phase lock detecting circuit 16 becomes high to prevent the reproduced video signal from being affected by the action of the time base correction circuit in the event of the large tracking error. Further, since the operation of the time base correction circuit is put to a pause only for a minimum necessary period of time, the reproduced video signal is obtainable with the time base correction circuit used as much as possible. The embodiment thus ensures that a video signal can be automatically produced in the best state.

The operation of the time base correction circuit can be promptly brought to a stop in the event of occurrence of an abnormality in the rotation of the drum during the process of building up of the drum rotation or due to some other reason. Therefore, the reproduced video signal can be prevented from being affected by such abnormality.

In accordance with the arrangement of the rotary head type reproducing apparatus embodying this invention as described in the foregoing, the time base correction circuit is allowed to automatically operate only when it is adequately operable. The arrangement prevents the reproduced signal from being deteriorated by any faulty action of the time base correction circuit. Besides, the embodiment is arranged to be capable of giving an adequately reproduced signal by accomplishing the time base correction to a maximum possible degree.