Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1994-02-14
2001-02-27
Rao, Andy (Department: 2713)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000
Reexamination Certificate
active
06195500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the phase control of a video cassette recorder (referred to hereinafter as VCR), and more particularly to a phase control apparatus for a VCR in which a control signal reproduced by a control head is amplified at a varied amplification gain and a phase of a capstan motor is accurately detected on the basis of the amplified control signal.
2. Description of the Prior Art
Referring to
FIG. 1
, there is shown a block diagram of a conventional phase control apparatus for a VCR. As shown in this drawing, the conventional phase control apparatus comprises a control head
20
for reproducing a control signal recorded on a control track under a video track of a tape
10
, and a control signal amplification circuit
30
for amplifying the reproduced control signal from the control head
20
at a predetermined amplification gain. The control signal amplification circuit
30
is provided with resistors R
1
and R
2
, condensers C
1
-C
3
and an amplifier OP
1
.
A control signal wave-shaping circuit
40
is provided in the phase control apparatus to wave-shape an output signal from the control signal amplification circuit
30
and stabilize the wave-shaped signal. The control signal wave-shaping circuit
40
includes a level limiter
41
for wave-shaping the output signal from the control signal amplification circuit
30
and a Schmidt trigger circuit
42
for stabilizing an output signal from the level limiter
41
.
A phase control circuit
50
is also provided in the phase control apparatus to detect an phase error and a rotation speed of a capstan motor CM in response to an output signal from the control signal wave-shaping circuit
40
and an output frequency from the capstan motor CM and output phase and speed detect signals in accordance with the detected results to allow a video head to accurately trace the video track of the tape
10
. The phase control circuit
50
includes a reference pulse generator
51
for generating a reference pulse signal, a phase detector
52
for comparing a phase of the output signal from the control signal wave-shaping circuit
40
and that of the reference pulse signal from the reference pulse generator
51
. detecting the phase error of the capstan motor CM in accordance with the compared result and outputting the phase detect signal in accordance with the detected result, and a speed detector
53
for detecting the rotation speed of the capstan motor CM in response to the output frequency from the capstan motor CM and outputting the speed detect signal in accordance with the detected result.
A capstan motor driving circuit
60
is also provided in the phase control apparatus to drive the capstan motor CM in response to the phase and speed detect signals from the phase control circuit
50
. The capstan motor driving circuit
60
is provided with a resistor R
3
, condensers C
4
and C
5
and an amplifier OP
2
.
The operation of the conventional phase control apparatus with the above-mentioned construction will hereinafter be described.
First, the control si-gnal recorded on the control track of the tape
10
is reproduced by the control head
20
and then applied to the control signal amplification circuit
30
. In the control signal amplification circuit
30
, the amplifier OP
1
amplifies the reproduced control signal from the control head
20
at the amplification gain determined by the resistors R
1
and R
2
and the condensers C
1
-C
3
. The output signal from the control signal amplification circuit
30
is applied to the control signal wave-shaping circuit
40
.
In the control signal wave-shaping circuit
40
, the output signal from the control signal amplification circuit
30
is wave-shaped by the level limiter
41
for removal of a noise component therefrom and then stabilized by the Schmidt trigger circuit
42
. The output signal from the Schmidt trigger circuit
42
is applied to the phase control circuit
50
.
In the phase control circuit
50
, the phase of the output signal from the Schmidt trigger circuit
42
is compared with that of the reference pulse signal from the reference pulse generator
51
by the phase detector
52
. As a result of the comparison, the phase detector
52
detects the phase error of the capstan motor CM and outputs the phase detect signal. Also, the output frequency from the capstan motor CM is applied to the speed detector
53
, thereby causing the rotation speed of the capstan motor CM to be detected by the speed detector
53
. As a result of the detection, the speed detector
53
outputs the speed detect signal.
The phase detect signal from the phase detector
52
is applied to a non-inverting input terminal (+) of the amplifier OP
2
in the capstan motor driving circuit
60
and the speed detect signal from the speed detector
53
is applied to an inverting input terminal (−) thereof. The amplifier OP
2
amplifies the phase detect signal from the phase detector
52
and the speed detect signal from the speed detector
53
at an amplification gain determined by the resistor R
3
and the condensers C
4
and C
5
. Then, an output signal from the amplifier OP
2
is applied as a drive signal to the capstan motor CM. As a result, the phase error of the capstan motor CM is corrected by the drive signal from the, capstan motor driving circuit
60
so that the video head can accurately trace the video track of the tape
10
.
The above-mentioned operation of the conventional phase control apparatus will hereinafter be described in detail with reference to
FIGS. 2
to
5
.
FIG. 2
is a waveform diagram of the output signal from the control signal amplification circuit
30
,
FIG. 3
is a waveform diagram of the output signal from the control signal wave-shaping circuit
40
,
FIG. 4
is a waveform diagram of the output signal from the reference pulse generator
51
in the phase control circuit
50
and
FIG. 5
is a waveform diagram of the output signal from the phase detector
52
in the phase control circuit
50
.
First, the control signal recorded on the control track of the tape
10
is reproduced by the control head
20
and then amplified by the control signal amplification circuit
30
, as shown in FIG.
2
. The output signal from the control signal amplification circuit
30
as shown in
FIG. 2
is wave-shaped and stabilized by the control signal wave-shaping circuit
40
, as shown in FIG.
3
. The output signal from the control signal wave-shaping circuit
40
as shown in
FIG. 3
is applied to the phase control circuit
50
.
In the phase control circuit
50
, the phase of the output signal from the control signal wave-shaping circuit
40
as shown in
FIG. 3
is compared with that of the reference pulse signal as shown in FIG.
4
. The phase detect signal as shown in
FIG. 5
is generated as a result of the comparison. When the video head traces accurately the video track, the phase detect signal as shown in
FIG. 5
is generated in the middle of a rising edge of the reference pulse signal as shown in FIG.
4
. But, in the case where the video head traces inaccurately the video track, the phase detect signal is generated before or after the middle of the rising edge of the reference pulse signal as shown in FIG.
4
. This signifies the generation of the phase error of the capstan motor CM. As a result, the capstan motor drive signal is generated to correct the phase error of the capstan motor CM.
However, in the case where the tape is bad in quality or the video head travels missing the video track of the tape, the reproduced control signal is low in level, thereby making the phase control difficult. Also, when a noise component is contained in the control head, it is reproduced and amplified together with the control signal, resulting in the difficulty in the phase control. These may result in a faulty operation of the VCR.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a phase control
Goldstar Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Rao Andy
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