Timing signal dropout compensation circuit

• US 4,680,651 A
• Filed: 08/19/1986
• Issued: 07/14/1987
• Est. Priority Date: 08/19/1986
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Blessinger, Kurt V.
• Primary Examiner(s): Cardillo, Raymond F.
• Assistant Examiner(s): Young, Wayne R.
• Application Number:
  US06/897,890
• Time in Patent Office: 329 Days
• Field of Search: 360/9.1, 360/11.1, 360/38.1, 360/51, 360/36.1, 358/310, 358/314, 358/327, 358/335, 358/336, 358/906, 358/213, 358/337, 358/320, 377/60, 331/25
• US Class Current: 386/271
• CPC Class Codes: H04N 5/7822 with stationary magnetic heads
• CPC Class Codes: H04N 5/919 by dividing samples or signal segments, e.g. television lines, among a plurality of recording channels
• CPC Class Codes: H04N 5/94 Signal drop-out compensation

Abstract

In video reproduction apparatus in which video information representing a scene is recorded in a plurality of longitudinal tracks on magnetic tape, a timing signal is also recorded in a timing track parallel to the video information tracks. A dropout in the timing signal reproduced from the timing track causes degradation in the reproduced scene. There is disclosed a circuit for compensating for dropouts in the timing signal track to reduce such reproduced image degradation. A phase lock loop circuit produces a video sampling signal which is phase locked to the reproduced timing signal, and which has a frequency that is a multiple of said timing signal. The phase lock loop circuit has a loop bandwidth which tracks variations in frequency produced by flutter. A timing signal dropout detector detects an out of lock condition of the reproduced timing signal and produces a control signal which causes the phase lock loop circuit to continue to produce a video sampling signal during the dropout period of the timing signal.

Claims

1. In video reproduction apparatus in which video information is recorded in a plurality of longitudinal video tracks on recording media, and in which a timing signal is recorded in a timing track parallel to the video information tracks, timing signal dropout compensation circuit comprising:

means for reproducing a timing track signal from said timing track on said recording media at it is moved past said reproducing means, wherein said timing signal is susceptible to changes in frequency caused by variations in speed of said recording media as it is moved past said reproducing means;

first phase lock loop (PLL) circuit means for producing a first phase locked timing signal which is phase locked to and has the same frequency as said timing track signal reproduced from said media, said first PLL circuit means including means for producing a dropout control signal which is a function of a loss of lock of said reproduced timing track signal caused by a dropout in said timing track signal;

second phase lock loop circuit means for producing a video sampling signal which is used in the reproduction of said video information from said media and which is phase locked to said first phase locked timing signal and which has a frequency which is a multiple of said first phase locked timing signal, said second PLL circuit means being responsive to said dropout control signal produced by said first PLL circuit means to continue to produce said video sampling signal during the period of said timing track signal dropout;

wherein said first and second PLL circuit means have loop bandwidths which are sufficient to follow frequency variations in the timing track signal reproduced from the recording media without loss of lock of the timing track signal.

2. The compensation circuit of claim 1 wherein said second phase lock loop circuit means includes a voltage controlled oscillator for producing a sampling signal having a frequency Mf and a sample and hold circuit which supplies a voltage control signal to said voltage controlled oscillator and wherein said sample and hold circuit is responsive to said dropout control signal to hold the last voltage control signal during the duration of the dropout of said reproduced timing track signal so that an uninterrupted sampling signal is produced by said voltage controlled oscillator during said dropout period.

3. In magnetic tape reproduction apparatus in which video information is recorded in a plurality of longitudinal video tracks on magnetic tape and in which a timing signal is recorded in a timing track parallel to the video information tracks, a timing signal dropout compensation circuit comprising:

means for simultaneously reproducing from said magnetic tape (1) a timing track signal from said timing track and (2) a plurality of video information signals from said video information tracks, wherein said timing track signal and said plurality of video information signals are susceptible to comparable changes in frequency caused by variations in speed (flutter) of said magnetic tape as it is moved past said reproducing means;

phase lock loop (PLL) circuit means for producing a video sampling signal which is used in sampling said video information signals, which has a frequency that is a multiple of the frequency of said timing track signal and which is phase locked to said timing track signal, wherein said PLL circuit means has a loop bandwidth which is sufficient to follow flutter induced frequency variations in said timing track signal without loss of lock thereof; and

means for detecting a dropout in said reproduced timing track signal and for producing a dropout control signal which causes said PLL circuit means to continue to produce said video sampling signal during the period of said timing track signal dropout.

4. The timing signal dropout compensation circuit of claim 3 wherein said dropout detecting means includes timing signal phase lock loop means for producing a first phase locked timing signal which is phase locked to and has the same frequency as said reproduced timing track signal and further includes means for detecting a loss of lock of said reproduced timing track signal and for producing said dropout control signal during detection of said loss of lock.