Note: Descriptions are shown in the official language in which they were submitted.
~3~99
1 gACKGROUND OF THE INVENTION
The present invention relates generally to systems for
reproducing recorded signals from recording mediums. More
particularly, the invention relates to a system for reproducing
1 a main information signal from a rotary recording medium. The
rotary recording medium is recorded with the main information
I signal including a video signal and an audio signal together with
reference signals, so that beat disturbance will not occur with
l respect to the video signal.
Known systems have heretofore recorded and reproduced
information signals such as video signals and/or audio signals
on and from disc-shaped recording mediums (hereinafter simply
referred to as "discs"). These known systems are broadly divided
I into systems in which reproduction is carried out optically,
¦ systems in which reproduction is carried out by means of a
reproducing stylus employing a piezoelectric element, and systems
in which reproduction is carried out by utilizing variations in
the electrostatic capacitance between an electrode on a reproducing
~ stylus and the recorded surface of the disc.
¦ We have considered the advantages and disadvantages of
i these three kinds of systems and have adopted the electrostatic
capacitance system as being the most desirable. E`urther, the
present applicant has previously proposed, as a new system for
l overcoming the problems accompanying known electrostatic
25 ; capacitance systems. Please see copending application entitled
"Information signal recording system" as disclosed in the
Canadian Patent Application Ser. No.275,672, filed April 6, 1977
which has been allowed on December 8, 1981.
l More specifically, in accordance with a known
e 1 ec tros tat ic c ap ac itarlc e sys tem, r ecord ing is sc compl ished
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499
1 by forming a spiral guide groove in the disc for guiding the
reproducing stylus. At the same time, pits are formed responsive
to and in correspondence with an information signal to be recorded
on the bottom surface of the groove. In the reproducing system,
~I the reproducing stylus, is guided by the guide groove. It traces
the track within the groove and reproduces the recorded signal
in response to variations in the electrostatic capacitance.
In this known system however, a reproducing stylus
guiding groove is provided in the disc ! The reproducing stylus
l is compulsorily guided by this groove ! It is not possible for
the reproducing stylus to do such things as riding over the
groove wall of one track, moving into another track, and then
returning to the original track. If the reproducing stylus
~ were to be forced to undergo such an operation, the goove and
1 the stylus would be damaged. For this reason, it has not been
possible in this known system to carry out quick-motion picture
reproduction, slow-motion picture reproduction, still-picture
reproduction, and the like.
~ Furthermore, since the contact area between the tip
1 of the reproducing stylus and the guide groove of the disc is
small, the stylus wears excessively. When the width of the
stylus tip reaches the groove width as a result of abrasive wear,
~ the serviceable like of this reproducing stylus ends. Thus,
i this systern is accompanied by the problem of a short life for
the reproducing stylus. Another problem is that fine chip
particles are abraded from the disc by the tracing action of the
reproducing stylus along the guide groove. These chips give rise
to difficulties which further promote wear and damage of the
stylus and the guide groove. As a result, there is an increase
of the gap between the electrode at the stylus tip and the
i~34~
I recorded surface including the pits within the disc guide groove.
The reproduced output decreases because of spacing loss.
If a low rotational disc speed (such as 450~rpm) is
used to prolong the life of the stylus tip, the recording
wavelength of the information signal recorded in the guide groove
will become short. For this reason, a low price recording
apparatus using a laser light cannot be employed in the recording
system. The disadvantageous result is that a high price recording
ll apparatus must use an electron beam.
Accordingly, to overcome the various problems of the
known systems described above, the aforecited patent application
describes a novel system for recording and reproducing information
signals. According to the recording in this system, pits are
formed in accordance with the information signal being recorded
along a spiral track on a recording medium of flat disc shape,
without forming a groove therein. In the reproducing system,
a reproducing stylus traces over and along time track to reproduce
the recorded information signal. In this system, pilot or
~ reference signals are recorded on or in the vicinity of a track
¦ of the information signal such as video signal on a rotary disc.
At the time of reproducing, the reference signals are reproduced
~together with the video signal. Tracking servo control is
carried out so that the reproducing stylus traces accurately along
the track in response to the reproduced reference signals.
By the use of this previous system, the recording
track has no groove. There is no possibility whatsoever of
the reproducing stylus or the recording medium being damaged.
The stylus can trace the same portion of the track repeatedly
~ many times. Therefore, special reproduction such as still, slow
motion, or quick motion reproduction becomes possible.
~ - 4 -
'i99
1 ~ Furthermore, other difficulties of the known system are removed.
If a video signal and an audio signal are to be
recorded as the main information signal, it is desirable to
Irecord the video signal and the audio signal on the same track
~ for effective utilization of the recording capacity of the
recording medium. Accordingly, known recording systems use a
duty-cycle modulation system. A frequency-modulated audio signal
obtained by frequency-modulating a carrier wave with an audio
signal is superimposed on a frequency-modulated video signal
obtained by frequency-modulating a carrier wave with a video
signal. The duty cycle of the carrier wave of the frequency-
modulated video signal is modulated by the carrier wave of the
frequency-modulated audio signal.
In this system, however, distortion in the signal
transmission system is great. Cross-modulation distortion arises
between the frequency-modulated video signal and the frequency-
modulated audio signal. As a result, beat disturbance occurs
jl in the demodulated video signal. For reducing this beat
l disturbance, the level of the frequency-modulated audio signal
is lowered relative to the frequency-modulated video signal.
However, this is not desirable since it gives rise to a ~owering
of the S/N ratio of the demodulated audio signal.
Furthermore, if a color video signal and an audio signal
~ are recorded on the same track, one conceivable method begins by
~separating the color video signal into a luminance signal and a
chrominance signal. The frequency-modulated audio signal and
the separated luminance signal are mixed. Then, a carrier wave
~is frequency-modulated with the resulting mixed signal. The
~system mixes and records the resulting frequency-modulated signal.
~ signal is obtained by irequency-convertinq the separated
~34~9
1 chrominance signal to a band which is lower than the frequency-
modulated luminance signal. By this method, however, the
chrominance signal which has been frequency-converted to a lower
frequency band is not frequency-modulated. This chrominance signal
cannot be passed through an amplitude limiter in the reproducing
system. There is a problem of its readily being affected by
level fluctuation.
On the other hand, if pilot signals are recorded in
correspondence with the horizontal blanking periods of the video
signal in the aforedescribed system, the pilot signals have
no disturbing effect whatsoever on the video signal. However,
the pilot signals may be used for tracking control of the reproduc-
ing transducer and also for correction control of time-axis error
(jitter) of the reproduced signal. The pilot signals may also
be used for arm-stretcher control by which the position of a
reproducing transducer is controlled in its longitudinal
direction along the track. The pilot signals are recorded in
correspondence with all periods of the video signal. In this
ll case, it is conceivable that the pilot signals may impart a beat
~ disturbance to the video signal. Therefore, there is a necessity
for preventing deleterious effects on the video signal even when
the pilot signals are recorded over all periods of the video
signal.
SUMMARY OF THE INVENTION
I . ~
Accordingly, it is a general object of the present
invention to provide a novel and useful system for reproducing
information signals from a recording medium. Here, an object is
~ to overcome the above described difficulties which are encountered
in ehe known sys eems .
1,
~34499
1 Another and specific object of the invention is to
provide a system capable of reproducing from the same track
a plurality of main information signals with little beat dis-
turbance. Then information signals may be for example, a video
signal and an audio signal. An object is to avoid such dis-
i turbance even when there is great distortion in the signal
transmission system is great.
Still another object of the invention is to provide
a system capable of reproducing pilot signals without producing
beat disturbance with respect to the above mentioned video signal.
Other objects and further features of the invention
will be apparent from the following detailed description when
read in conjunction with the accompanying drawings.
sRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG.1 is a block diagram of one example of a recording
apparatus for recording signals on a rotary recording medium
~ which is reproduced by a system of the invention;
1 FIG.2 is a block diagram of one example of a recording
system;
FIG.3 is a block diagram, in greater detail, showing
one part of the system shown in FIG.2;
FIGS.4A, 4B, and 4C are respectively graphs indicating
~ the frequency spectrum of signals at various parts of the block
diagram of the system illustrated in FIG.2;
FIGS.5A and 5B are fragmentary plan views showing
portions of a track pattern on a rotary recording medium on
¦ which signals have been recorded by the recording apparatus shown
in FIG.1;
1~34~99
1 , EIG.6 is a greatly enlarged perspective view showing
, the tracking of a reproducing stylus on a rotary recording medium;
FIG.7 is a perspective view of one example of a
I reproducing transducer;
FIG.8 is a block diagram of one embodiment of the
reproducing system of the invention; and
FIG.9 is a block diagram of one embodiment of a time-
~ axis error correction circuit.
I DETAILED DESCRIPTION
I
FIG.1 shows one example of an apparatus for recording
a signal on a rotating recording medium. A laser light beam is
¦l emitted from a laser light source 11 and is reflected by a
¦ mirror 12 through a light modulator 13 for light quantity
~ adjustment. The light beam thus adjusted is projected onto a
half mirror 14, which transmits one part of the light to a light
modulator 15 and reflects another part thereof to another light
modulator 16.
~ A main information signal is obtained from a circuit
¦ which will be described hereinafter. This signal is supplied
through an input terminal 17 to the light modulator 15 which
modulates the light beam transmitted through the half mirror 14.
The resulting output is projected as a first modulated light beam
~ onto a mirror 1~, by which it is reflected. It passes through
~ a polarizing prism 19. The light transmitted through the prism
19 is reflected by a mirror 20 through an objective lens 24.
There it is brought to a focus on a photosensitive agent coating
an original recording disc 25 made of material such as glass.
¦ On the other hand, reference signals are obtained from
30 ~ the c i rcu it wl ich wil 1 be des c r lb;d her e inaf ter . Thes e s iqna ls
1 are supplied through an input terminal 26 to the light modulator
16.
The light beam reflected by the half mirror 14 is
modulated in the light modulator 16 by the pilot signals. A
mirror 27 reflects the resulting output, as a second modulated
light beam, into the polarizing prism 19, where its polarization
I plane is angularly shifted by 90 degrees from that of the first
! modulated light beam. Leaving the polarizing prism 19, the first
I and second modulated light beams are reflected by the mirror 20
through the objective lens 24, and are focused on the original
recording disc 25.
The original disc 25 is mounted on a turntable 28,
and is rotated at a rotational speed of, for example 9OO rpm,
l by a motor 29. The original disc 25, turntable 28, and motor 29
1 are unitarily and continuously transported at a specific pitch
in the arrow direction X by a transporting mechanism (not shown).
As a result, the first and second modulated light beams record
the main information signal and the pilot signals along a spiral
l track on the original disc, the track extending from an outer
~ periphery of the disc toward its center.
Furthermore, a displacement position detector 30
(comprising a potentiometer) detects the displacement position
due to the transporting movement as the original disc 25 and the
l turntable 28 are transported in the arrow direction X. The
potentiometer produces a DC voltage responsive to the displace-
ment position. This DC voltage is passed through a DC amplifier
31 to the light modulator 13 for light quantity adjustment.
The intensity of the light beam from the laser light source 11
is controlled in response to the position, in the radial direction
of t e original disc 25, of the l ght beam spot focused on the
Il
11;.~4499
l ~ disc 25. By this arrangement and operation of the recording
apparatus, compensation eliminates the effect of the difference
in linear speed due to the position of the light beam spot in
~ the radial direction of the original disc 25.
~ The original disc 25 is exposed to light, subject to
a known developing process and to a known disc fabricating
process, whereupon a completed recorded disc is obtained. The
recorded disc comprises, for example, a disc substrate made of
polyvinyl acetate (PVAC), in which the pits are formed in the
10 ~ spiral track. A metal coating is formed over the substrate
j with a thickness of 400 A, for example, to constitute an
electrode. A dielectric coating film of a thickness of 400 A
is adhered onto the metal coating. The disc may be given an
~ electrode function by using another material instead of a metal
¦ coating film.
It is to be observed that an electron beam may be used
in place of ~ laser light beam. Furthermore, instead of the
arrangement wherein the original disc, turntable 28, and motor 29
~ are transported in the arrow direction X, an arrangement may
~ be provided wherein an optical system for projecting the light
beams onto the original disc 25 is transported in the direction
opposite to the arrow direction X.
FIG.2 shows on example of an essential part of the
~ recording system for forming signals supplied to the input
¦ terminals 17 and 26.
The stereo audio signals of two-channels are supplied
from audio signal sources 41 and 42 to frequency modulators 43
and 44. There, they frequency-modulate carrier waves respectively
ll of frequencies of 3.43 MHz and 3.73 MHz, for example. The
~ resulting frequency-modulated audio signals fA1 and fA2 have
li;34493
l frequency deviations of 3.43 MHz + 75 KHz and 3.73 MHz + 75 KHz
and are supplied to a mixer 45.
On the other hand, an NTSC color video signal, for
I example, is supplied from a color video signal source 46 to
1 each of two comb filters 47 and 48. The comb filter 47 operates
with respect to signals in a frequency band higher than 2 MHz
and separates a luminance signal, which is supplied to a low-pass
filter 49. This low-pass filter 49 band limits the upper
l frequency of the luminance signal to approximately 3 MHz. The
resulting output luminance signal has a frequency spectrum
shown in FIG.4A, and is supplied to a mixer 50 and to a synchro-
nizing signal separation circuit 51. The circuit 51 separates
a synchronizing signal from the luminance signal.
~ The comb filter 48 produces a carrier chrominance
15 1 signal having a frequency spectrum shown in a full line in FIG.4B.
A frequency band of 3.58 MHz + 500 KHz is supplied to a color
sub-carrier generating circuit 52 and to a frequency converting
circuit 53. The color sub-carrier generating circuit 52, which
~is known, generates a continuous wave of a frequency fsc
~ (3.579545 MHz in the case of a NTSC system color video signal).
~The frequency fsc is equal to the color sub-carrier frequency
of the carrier chrominance signal, and is generated from a color
burst signal in the carrier chrominance signal from the comb
filter 48. The signal uses a burst gate pulse signal formed
from the synchronizing signal from the synchronizing signal
separation circuit 51.
The frequency converting circuit 53 frequency-
~demultiplies and frequency-multiplies the signal of the frequency
fsc from the color sub-carrier generating circuit 52. This
obtains a signal of a frequency of 12/7 fsc and beat converts
~:134~99
~'
1 this signal and the input carrier chrominance signal. As a
result, the frequency converting circuit 53 produces a carrier
chrominance signal which results from the frequency conversion
lof the color sub-carrier frequency to low band cf 5/7 fsc
(approximately 2.56 MHz) and a frequency spectrum shown in an
intermittent line in FIG.4B.
This low-band converted carrier chrominance signal is
supplied to the mixer 50. There it is multiplexed and inserted,
I in a common band frequency band near the upper limit frequency
~ of the luminance signal, with the luminance signal shown in
FIG.4A. The luminance signal is obtained from the comb filter
47 and band limited by the low-pass filter 49. This multiplexed
l~ signal passes through a pre-emphasis circuit 54 to the mixer 45.
There it is mixed at a suitable level ratio with the frequency-
~ modulated audio signals fA1 and fA2.
~ In this connection, the carrier frequencies of these
¦ frequency-modulated audio signals fA1 and fA2 have values higher
than the upper-limit frequency (3 MHz) of the luminance signal
band. There will be no overlapping of bands with the luminance
1 signal which has been separated and band limited. Here, it is
desirable that these carrier frequencies be of values which are
not very high. For example, they may be in the order of 3 to
4 MHz, because of considerations such as relationships with the
I other recorded and reproduced signals and the facility of
recording and reproducing.
The output mixed signal of the mixer 45 is supplied
to a frequency modulator 55, where it frequency-modulates a
I carrier. Here, this frequency modulation is carried out so
that, for example, the synchronizing signal tip (sync. tip) of
the video signal will be 6.0 MHz, the pedestal will be 6.7 MHz,
- 12 -
113'-499
I and the white peak will be 8.3 MHz. The output frequency-
modulated signal of this frequency modulator 55 is led out as
a main information signal through an output terminal 56. It
I is supplied to the input terminal 17 of the system shown in
I FIG.1 and then recorded on a main information signal track of
the disc 25.
Thus, in the above recording system, the known duty-
cycle modulation system is not used. A single carrier is
l frequency-modulated by signals such as a luminance signal,
a carrier chrominance signal, and a frequency-modulated audio
signal. For this reason, cross modulation distortion does not
occur in the reproduced demodulated video signal, even when there
is great distortion in the recorded and reproduced signal
~I transmission system. Therefore, beat disturbance does not arise.
1 A color video signal and an audio signal can be recorded on the
same single track.
On the other hand, a pilot signal generating circuit
57 is supplied with a synchronizing signal from the synchronizing
signal separation circuit 51 and the color sub-carrier signal
of the frequency fsc from the color sub-carrier generating
circuit 52. The circuit 57 produces first, second, and third
pilot signals fp1, fp2, and fp3, as described hereinafter.
These pilot signals are led out through an output terminal 58
and supplied to the input terminal 26 of the system shown in FIG.1.
The third pilot signal fp3 may be led out through
another output terminal 59, and supplied to the input terminal
17 (FIG.1) together with the main information signal from the
output terminal 56. The third pilot signal fp3 is thus recorded
l on the main information signal track, as described hereinafter.
A detailed block system of one example of the pilot
113~99
1 signal generating circuit 57 will now be described in conjunction
with FIG.3. The synchronizing signal from the synchronizing
signal separation circuit 51 is applied through an input terminal
71 to a horizontal synchronizing signal separation circuit 72,
I to a vertical synchronizing signal separation circuit 77, and to
a J-K flip-flop circuit 81. The horizontal synchronizing
signal separated by the separation circuit 72 is applied as a
trigger pulse to a monostable multivibrator 73. The output of
the monostable multivibrator 73 is applied as a trigger pulse
1 to another monostable multivibrator 74. As a result, the
monostable multivibrator 73 adjusts a pulse signal to a suitable
position and the monostable multivibrator 74 gives the pulse
a suitable width. The resulting pulse is supplied from the
monostable multivibrator 74 to J-K flip-flop circuits 75 and 76.
The vertical synchronizing signal which has been
separated by the circuit 77 is passed through a counter 78,
where its frequency is counted down to 1/4 and thus frequency
divided. The pulse is then supplied as a trigger pulse to a
monostable multivibrator 79. This monostable multivibrator 79
thereupon produces an output which triggers another monostable
multivibrator 80. This produces an output pulse signal which
has been adjusted to a suitable position and a suitable width,
respectively, by the monostable multivibrators 79 and 80. The
Q and Q output pulses of the monostable multivibrator 80 are
supplied to input terminals J and K of the J-K flip-flop circuit
81. The position of this output pulse is adjusted to be within
the vertical blanking period such as the equalizing pulse position
immediately after the vertical synchronizing signal. The output
pulse width has a value in the order of lH (where H is the
1 horizontal scanning period) to a multiple of H.
11;34499
1 The J-K flip-flop circuit 30 is operated by a synchro-
nizing signal applied as a clock pulse through the input terminal
71 to re-synchronize the output signal of the monostable
multivibrator 80. The resulting output of the J-K flip-flop
circuit 81 is supplied to a flip-flop circuit 82, to gate
circuits 83 and 84, and to a J-K flip-flop circuit 95. The
flip-flop circuit 82 counts down its input signal and produces
a rectangular output wave which repeats a logical "O" and "1",
l~ with a period or a duration corresponding to four fields of the
video signal. This rectangular output wave is applied as gate
pulses of mutually opposite phase respectively to the gate
circuits 83 and 84. The pulse part of the output from the J-K
flip-flop circuit 81 is a gate output.
ll A continuous wave signal, of the frequency fsc, is
¦ produced by the color sub-carrier generating circuit 52 and is
~ supplied through an input terminal 87 to a waveform shaping
¦ circuit 88. There it is formed into a rectangular wave. The
resulting rectangular output wave is counted down respectively
l to 1/13, 1/5, and 1/7, and thus frequency-divided by counters
1 89, 90, and 91. In this case, the output signals of the
counters 89, 90, and 91 have a frequency-interleaving relation-
ship to the frequency fH of the horizontal synchronizing signal.
The frequencies 511.36357 KHz (=3.579545 MHz x 1/7) and
715.909 KHz (=3.579545 MHz x 1/5) are obtained respectively
from the counters 90 and 91 and are applied as clock pulses
respectively to the J-K flip-flop circuits 75 and 76. The
Q and Q output signals of the monostable multivibrator 74 are
applied to the J and K input terminals of the flip-flop circuits
75 and 76. As a result, the output of the monostable multivib-
rator 74 is re-synchronized by the outputs of the counters 90
1 5
1134'199
1 and 91 and is supplied to gate circuits 85 and 86. In this case,
the output signals of the counters 90 and 91 have a frequency-
interleaving relationship to the horizontal synchronizing signal.
They also have varying phases relative to the output of the
monostable multivibrator 74. For this reason, the J-K flip flop
circuits 75 and 76 are used for re-synchronization.
The outputs of the gate circuits 83 and 84 and the
outputs of the counters 90 and 91 are further supplied to
the gate circuits 85 and 86. As a result, pulses are obtained
with a 4-field period from these gate circuits 85 and 86, during
the horizontal blan]cing intervals, exclusive of the output width
intervals of the J-K flip-flop circuit 81. The outputs of the
gate circuits 85 and 86 are applied as trigger pulses to
! monostable multivibrators 92 and 93 t From them, first and second
pilot signals are obtained at the frequencies 715.909 KHz and
511.36357 KHz, with a duty cycle of 50 percent. They are respec-
tively supplied to a mixer 94.
The Q and Q outputs of the J-K flip-flop circuit 81
are applied to the J and K input terminals of the J-K flip-flop
circuit 95. The counter 89 produces a signal at a frequency
; of 275.3496 KHZ (=3.579545 MHz x 1/313) which is applied as a
clock pulse. A gate circuit 96 receives the output pulse of the
J-K flip-flop circuit 95 as a gate pulse and thereby gates the
~ signal from the counter 89. The resulting output of the gate
I circuit 96 triggers a monostable multivibrator 96, which there-
upon produces the third pilot signal fp3 at a frequency of
275.3496 KHz and with a duty cycle of 50 percent. This third
pilot signal fp3 passes through a switch 98, whose moving
l contract is connected to the side of its fixed contact a, and
is supplied to the mixer 94.
- 16 -
I
499
1 ~I The first, second, and th rd pilot signals fp1, fp2,
and fp3 are mixed in the mixer 94. The resulting output is
led out through the output terminal 58 to the input terminal 26
of the system in FIG.1. Since the first, second, and third pilot
signals are obtained by counting down the color sub-carrier in
; this manner, the frequency and the phase are stable.
Since the third pilot signal fp3 exists in only the
vertical blanking interval, it may be recorded on the track of
the main information signals. Therefore, if it is thus recorded,
¦ the moving contact of the switch 98 is connected to the fixed
contact b! The third pilot signal is led out through the terminal
59 to the input terminal 17 of the system shown in FIG.1.
In the above described example, the first and second
pilot signals exist only during intervals corresponding to the
horizontal blanking intervals. However, these pilot signals
are respectively set by the counters 89, 90, ana 91 at the
frequencies which are odd-number multiples of 1/2 of the
horizontal scanning frequency fH. They have a frequency-
interleaving relationship to the horizontal synchronizing signal.
Their frequency bands differ from that of the carrier chrominance
signal which has been converted to a low band. For this reason,
it is possible to continuously record the pilot signals fp1 and
fp2, at a high level so as to obtain a satisfactory S/N ratio.
~ The high level is taken in correspondence with the entire
duration of the video signal. The accuracy and stability of the
tracking control of the reproducing transducer can be improved
continuously by using the reproduced pilot signals. Furthermore,
these reproduced pilot signals can be used continuously to control
l the time-axis error (jitter).
1 One example of a frequency spectrum of main information
11 34~99
1 ~ signals and pilot signals which are recorded in the manner
described above is indicated in FIG.4. In this frequency
spectrum, the zone I indicates a carrier frequency deviation
band having a band width of 2.3 MHz of the frequency-modulated
luminance signal. The frequencies fa~ fb~ and fc respectively
indicate the frequencies of a 6 MHz corresponding to the tip
of the synchronizing signal, 6.7 MHz corresponding to the
pedestal, and 8.3 MHz corresponding to the white peak of the
l video signal. The zones III and IIU respectively indicate the
lower side band and the upper side band of the frequency-modulated
luminance signal. The zones IIIL and IIIU respectively indicate
the lower side band and the upper side band of signals obtained
I when the frequency-modulated audio signals fA1 and fA2 are further
~ frequency modulated. As described hereinbefore, the frequency
modulated audio signals fA1 and fA2 are obtained by frequency-
modulating carriers of frequencies of 3.43 MHz and 3.73 MHz
with an audio signal. These signals are indicated by the zone IV
which has a band that is higher than the luminance signal having
the upper limit frequency of 3 MHz. The zone V indicates the
band of the carrier chrominance signal converted to a low frequency
i band and is a band of 2.5568 MHz (=(5/7)fsc) i 500 KHz. First
side bandsand second side bands are produced by the frequency
~modulation of this carrier chrominance signal converted to a
low band. These side bands are indicated respectively by the zones
~ VIL and VIU and the zones VIIL and VIIU. The pilot signals
fp1, fp2, and fp3 are in a band lower than the bands of these
main information signals. The frequency spectrum indicated by
full lines in FIG.4 is the spectrum of signals which are actually
recorded.
FIGS.5A and 5s show an example of a disc produced by
1134~99
1 the recording apparatus illustrated in FIG.1. In FIG. 5A, the
recorded disc 110 has a spiral track formed thereon. One portion
of the circular disc shape is shown enlarged in FIG. 5B . In
FIG. 5B, the successive track turns, of the single continuous
I spiral shape, are respectively designated as t1~ t2, t3
Each track turn is constituted by the formation of pits 111
responsive to the main information signal along the track path.
With respect to one track turn t1~ every period H is shown at
a position (H.BLK), corresponding to the horizontal blanking
period. Pits 112 of the first pilot signal fpl are formed on
one lateral side of the track as viewed in the track path direc-
tion (for example, on the right hand side in the direction of
rotation). Pits 113 of the second pilot signal fp2 are formed
~ on the other side (left hand side) of the track. With respect
to the adjacent track t2, the pits 113 of the second pilot signal
fp2 are formed on one side (right hand side), as viewed in the
track path direction. The pilot signal is recorded at a position
corresponding to the horizontal blanking period in every period
H . On the other side (left hand side), the pits 112 are formed
responsive to the first pilot signal fp1. Thus, the positions
at which the pits 112 and the pits 113 of the first and second
pilot signals fp1 and fp2 are formed are alternately reversed
in the disc radial direction.
In addition, pits 114 of the third pilot signal fp3
~ are formed in the position (V.BLK) corresponding to the vertical
¦ blanking period, coinciding with the parts where the track turn
designation numbers change.
In the above example, the pilot signal pits 112 and
113 are formed at only the position H.BLK within one H period.
They re nOt formed at other parts 1 5, but the pit~ 112 and 113
113~499
1 may also be formed in these parts 115. The surface is planar
on those parts of the disc 110 in which pits are not formed and
they do not have a guide qroove.
~Moreover, in the above example, the pits 111 are so
I formed that one of the edge lines of each track is substantially
coincident with the nearest edge line of the adjacent track.
That is, the adjacent tracks t1r t2, t3,.... are so formed that
they are successively contiguous. Accordingly, the track pitch
TP is substantially equal to the track width TW. At central
¦ positions approximately intermediate between the centerlines
of the mutually adjacent tracks, pilot signal pits 112 and 113
are formed and overlapped on two tracks adjacent each other.
FIG.6 shows a reproducing stylus 120 tracing a track
recorded on the disc 110, having the above described pit
~ arrangement. Only the bottom face 121 of the stylus 120 and the
bottom face of an electrode 122 are shown. The bottom face 121
i of the stylus has a part with maximum width SW, which is greater
than the track pitch TP of the dise 110. An electrode 122 has
a thickness of 500 - 3000 ~ and is fixed to the rear faee of the
stylus at the rear edge of the bottom faee 121. As the dise 110
rotates in the arrow direction Y, the reproducing stylus 120
traces along the surface of the disc 110. The electrostatic
capacitance between the electrode 122 and an electroconductive
layer covering the entire surface of the disc varies in response
to the pits 111. The main information signal recorded by the
l pits 111 is thus reprodueed.
! At the same time, the eleetrode 122 also reproduces
the pilot signais of frequencies fp1 and fp2 recorded by the
~ pits 112 and 113. If the center of the electrode 122 deviates
~ from the centerline of the track, a level difference occurs in
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~134~9
l ~ the reproduced pilot signals. The tracking servo operation is
carried out by a circuit to be described hereinafter.
The reproducing transducer 130 has an arrangement as
shown in FIG.7, for example. A cantilever 131 has a reproducing
! stylus 120 mounted at its free end. At its opposite end the
cantilever 131 is connected via a damper 132 to a bracket 133.
The electrode of the reproducing stylus 120 is connected through
l a very thin lead wire 134 which is flexible and slackened to a
i terminal 136 on the support plate 135. A very thin gold wire
1 137 is bonded, except at its ends, to the cantilever 131 over
a specific distance along the longitudinal direction. Lead
wire parts 137a and 137b at the ends of this gold wire 137 are
respectively connected in a slackened state to terminals 138a
and 138b on the support plate 135. A permanent magnet 139 is
secured by way of a bracket 140 to the lower surface of the
support plate 135. The wire 137 is thus disposed in this strong
magnetic field formed by the magnet 139.
The tracking control signal is supplied between the
~ terminals 138a and 138b. When the control signal current flows
¦ through the terminals 138a and 138b and through the wire 137,
a displacement force acts on the wire 137 in the transverse
direction perpendicular to the longitudinal direction of the
¦ cantilever 131. This signal is in response to the current,
¦ according to the Fleming's left-hand rule, since the wire 137
~ is disposed within the field of the magnet 139. The cantilever
131 is displaced by the force acting on the wire 137 bonded
thereto. As a result, the reproducing stylus 120 is displaced
in a direction perpendicular to the longitudinal direction of
the track. Tracking control is so accomplished that the
~ reproducing stylus 120 traces accurately along the track.
1134499
~ ext, the block diagram of one embodiment of the
reproducing s~stem of the invention will be described in conjunc-
tion with FIG.8. The stylus 120 reproduces a signal from the
disc 110 responsive to a variation of electrostatic capacitance.
5 , The signal from the reproducing stylus 120 is passed through a
pre-amplifier having a resonance circuit whose resonance frequency
varies in response to the variation of electrostatic capacitance.
Then the signal is applied to an input terminal 151 of this
reproducing system. The reproduced signal thus introduced through
the input terminal 151 is fed to a low-pass filter 152 and to
a band-pass filter 161.
The first, second, and third pilot signals fp1, fp2,
and fp3 are obtained from the low-pass filter 152 are supplied
to an automatic gain controI (AGC) circuit 153. There their
levels are adjusted to specific values, and are then supplied
to amplifiers 154, 155, and 156. These amplifiers 154, 155,
and 156 are a kind of band-pass amplifiers having steep tuning
frequency characteristics at only the frequencies of the pilot
signals fp1, fp2, and fp3, respectively. The first and
second pilot signals fp1 and fp2 are obtained from the amplifiers
154 and 155 and are supplied to a tracking servo circuit 159.
The third pilot signal fp3 is obtained from the
¦ amplifier 156 and is passed through a detection circuit 157 to
~ trigger a flip-flop circuit 158. The output of flip-flop
1 circuit 158 is a rectangular wave which repeats a logical "0"
and "1" with a phase such that the pilot signal fp3 exists every
revolution of the disc 110. The output signal of the flip-
flop circuit 158 is supplied to the tracking servo ci~cuit 159
and switches the polarities of the first and second pilot
signals fp1 and fp2. The output of the tracking servo circuit 159
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1134~99
1 produces a tracking control signal responsive to the difference
between the levels of the first and second pilot signals thus
switched. This control signal is led out through a terminal 160
and applied to the terminals 133a and 138b of the system shown
in FIG.7.
On the other hand, the main information signal
component from the band-pass filter 161, where the pilot signals
have been removed, is demodulated by a frequency-demodulation
circuit 162. The resulting demodulated signal has frequency-
modulated audio signals fAl and fA2. The low-band converted
carrier chrominance signal, and the band-limited luminance
signal are mutually superimposed. This demodulated signal is
supplied to a separation circuit 163, where the low-band converted
carrier chrominance signal and the luminance signal are separated
out.
The separated low-band converted carrier chrominance
signal is supplied to a frequency converting circuit 164. There,
a component of a beat signal is removed. The beat difference
~ is relative to a signal of a frequency 12/7 fsc produced from
~ a signal of a frequency f 5/7 fsc from a variable-frequency
oscillator (VFO) 166. The carrier chrominance signal is
frequency-converted into the original carrier chrominance signal
whose color sub-carrier frequency is fsc. The output signal of
the frequency 5~7 fsc of the VFO 166 is supplied to a counter
167. There its fre~uency is counted down by 1/5 and made into
a frequency of 1/7 fsc, and is then supplied to a phase
comparator 165. The second pilot signal of the frequency of
I 1/7 fsc from the amplifier 155 is supplied to this phase
comparator 165 and is phase compared with the signal from the
~ counter 167. The output phase-compared error signal is applied
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113449~
I to the VFO l66 to control the oscillation frequency thereof.
As a result, the jitter component is removed from the carrier
chrominance signal during the frequency conversion.
The luminance signal separated at the separation
circuit 163 is supplied, through a low-pass filter 168 having
an upper cut-off frequency of approximately 3 MHz, to a mixer
169. There, it is mixed with the carrier chrominance signal
obtained from the frequency converting circuit 164. The
i reproduced color video signal obtained from the mixer 169 is
1 derived from an output terminal 169.
The output signal of the demodulator 162 is supplied
to band-pass filters 170 and 171 in which the frequency-
modulated audio signals fA1 and fA2 are filtered out. The
~ frequency modulated audio signals are demodulated at frequency
demodulators 172 and 173, whereby the demodulated audio signals
are derived from output terminals 174 and 175.
If the pilot signals fp1 and fp2 are continuously
recorded not only in the horizontal blanking period but also in
other periods of the video signal, it is possible to perform
jitter correction with the reproduced reference signal. In
this case, the system shown by the block diagram of FIG.9 may
be added to the block system of FIG.8.
The first and second pilot signals fp1 and fp2 are
obtained from the amplifiers 154 and 155, respectively, and are
~ supplied through input terminals 180a and 180b to ringing
oscillators 181 and 182 which form them into continuous wave
signals. The resulting output signals are supplied through
amplitude limiters 183 and 184 to frequency discriminators
l 185 and 186 and frequency-discriminated thereat. The
~ discriminated signals are mixed at a mixer 187 having an output
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113~4!99
1 terminal 188. The output signal is supplied as a control signal
; to a known jitter correction mechanism (not shown) called an
arm-stretcher. The jitter correction mechanism slightly moves
the reproducing stylus 120 in a longitudinal direction along
I the length of the track in response to the control signal.
This movement prevents the time-axis error from occurring in the
reproduced signal.
In the above described embodiment, the NTSC system
color video signal is employed as the color video signal which
is recorded~ The frequencies of the pilot signals are selected
in accordance with the carrier chrominance signal of the NTSC
system color video signal. However, the PAL system or SECAM
system color video signal may be employed. In this case,
frequencies of the pilot signals may be selected in accordance
with these color video signal systems.
The system according to the present invention may
be adopted in a magnetic reproducing system.
Further, this invention is not limited to these
embodiments but various variations and modiflcations may be
made ithout departing from the scope oi the invention.
~0
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