Time-base corrector

Details Time-base corrector Time-base corrector

1985-12-20

1988-03-22

Faber, Alan

Dynamic magnetic information storage or retrieval

Record editing

358336, 358337, 358339, 360 361, 360 362, 360 381, 360 371, H04N 5783, H04N 593

Patent

active

047333120

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a time-base corrector for a video tape recorder (VTR) capable of slow-motion reproduction.


DESCRIPTION OF THE PRIOR ART

In a broadcasting station or the like where it is necessary to render the reproduction video signal from VTR coincide with a reference sync signal of the station before transmission, a time-base corrector as shown in FIG. 1 is Indispensable.
In FIG. 1, a reproduction video signal 1 from VTR or like is supplied to both an analog-digital converter (A/D) 2 and a sync separator circuit 3. The sync separator circuit 3 supplies a write clock generator circuit 6 with a reproduction sync signal 4 separated from the reproduction video signal, and a latch circuit 7 with a reproduction vertical sync signal (hereinafter referred to as the tape V signal) 5. The write clock generator circuit 6 supplies a clock locked to the horizontal sync signal to the A/D 2 and a memory circuit 8 on the one hand and a signal (f.sub.H) 10 of the horizontal sync period to a write line address counter 9 on the other hand. Also, a read clock generator circuit 11 produces a clock on the basis of a reference sync signal 12 from an external source and applies the same to the memory circuit 8 and a digital-analog converter (D/A) 13, while at the same time applying a vertical sync signal (hereinafter referred to as the VP signal) and a horizontal sync signal (F.sub.H) 15 contained in the external reference sync signal to a read line address counter 14. The write line address counter 9 and the read line address counter 14 count the f.sub.H and F.sub.H signals respectively to prepare a line address, which line address is applied to the memory 8 through a switch circuit 17. The latch circuit 7 fetches the write line address when the tape V signal is applied thereto, and loads the fetched line address on the read line address counter 14 when the VP signal 16 is applied thereto, thereby rendering the write line address with the tape V signal 5 applied thereto coincide with the read line address with the VP signal 16 applied thereto.
Nevertheless, the reproduction video signal 1 from VTR may sometimes lacks the tape V signal 5 due to a dropout or like. In such a case, the operation of the latch circuit 7 becomes unstable, with the result that the output video signal of the time-base corrector fluctuates vertically on the monitor screen.
In the case of VTR carrying a movable head for the purpose of noiseless slow motion, on the other hand, two tape V signals 5 may appear in succession in a field or may not appear at all as described later. It is also impossible to obtain a stable image in such a case, too.
Specifically, in the VTR for performing noiseless slow-motion reproduction with a movable head, the time intervals of adjacent V signals are not fixed, but two V signals may appear successively or a very irregular V signal is generated. Now, the process of generation of an irregular V signal will be explained with reference to FIGS. 2 and 3.
FIG. 2 is a schematic diagram showing the manner in which the tape and video heads of the 2-head helical scan VTR run. The two heads including A head 18 and B head 19 are mounted at positions 180.degree. opposite to each other on the circumference of a rotary cylinder 20, and rotate in the direction of arrow 21. A magnetic tape 22 is wound by more than 180.degree. on the rotary cylinder 20 and runs in the direction of arrow 23.
FIG. 3 shows a recording pattern on the tape formed by the heads. The magnetic tape 22 runs along the direction of arrow 23, while the A head 18 and B head 19 are driven in the direction of arrow 21 alternately thereby to trace the recording tacks 24, 25 and 26 in that order on the magnetic tape 22. In the drawing, parts 24', 25', 26'; 24", 25", 26" designated by dashed lines represent overlapped recording area. In order to eliminate any discontinuities of the video signal in joint portions of the reproduction video signal from A head 18 and B head 19 at the time of reproduction, the magnetic tape 22 is wo

REFERENCES:
patent: 4251830 (1981-02-01), Tatomi
patent: 4409627 (1983-10-01), Eto

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