Controlling the phase of a frequency-modulated wave so as to be in a predetermined phase relationship with a video signal

A video tape recorder wherein when a video signal is frequency-modulated, the phase of a frequency-modulated wave is in a predetermined phase relationship with respect to the video signal. The frequency modulator is driven so that the video signal is time-base compressed to form a space of time. Then, a non-video signal is inserted into the space of time, and the frequency-modulated wave is brought into a predetermined phase having a synchronous relationship with the video signal. Furthermore, in another arrangement, during the reproducing operation, a regenerative demodulated signal is time-base expanded in order to avoid outputting noise due to the discontinuity in phase of the frequency-modulated wave which has arisen within the non-video signal contained space of the regenerated demodulated signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a video tape recorder arranged such that 
when a video signal is frequency-modulated, the phase of a 
frequency-modulated wave is in predetermined phase relationship with 
respect to the video signal. 
2. Description of the Prior Art 
Prior Art Japanese Patent Publication No. 53-9507 discloses that the 
interleaving of crosstalk from adjacent tracks is achieved by maintaining 
a predetermined relationship between the phase of the frequency-modulated 
wave and the input video signal. However, if a frequency modulator is 
forced into being reset when the frequency-modulated wave is put in a 
predetermined phase, the frequency-modulated wave will become 
discontinuous, so that a noise spike may be produced at the time when the 
frequency-demodulation takes place. 
Conventionally, such resultant spike noise would be subjected to a muting 
process. But this may cause a partial dropout of the spike noise at the 
time of the subsequent muting operation. 
That is, there lies a problem in that control of the frequency modulated 
wave to place it in any desired phase will lead to the partial dropout of 
demodulated video signals. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided an arrangement that 
when the video signal is frequency-modulated, the frequency modulator is 
driven so that the video signal is time-base compressed to form a space of 
time; then, a non-video signal is inserted into said space of time and the 
frequency-modulated signal is placed into a predetermined phase having a 
synchronous relationship with the video signal. Furthermore, another 
arrangement in accordance with the present invention is that by time-base 
expanding a frequency-demodulated signal, noise due to a discontinuity in 
phase of a frequency-modulated wave which has been generated by the 
frequency-demodulated signal within the non-video signal contained space 
can be eliminated. 
The described arrangement makes it possible to effectively control the 
frequency-demodulated wave so as to place it in any desired phase without 
consequential dropout of the video signals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1(a)-1(b) are a block diagram of a video tape recorder of the present 
invention, in which FIG. 1(a) shows a recording system, and FIG. 1(b) 
shows a reproducing system. The waveforms of the respective parts shown in 
FIGS. 1(a)-1(b) are illustrated in FIGS. 2(A)-2(G). An input video signal 
a from a terminal 1 is time-base compressed at a time-base compression 
circuit 2 to change it into a signal b. At this time, for example, a 
non-video signal c of a certain pattern is inserted into an area t of a 
space of time. 
In a control signal generating circuit 14, a horizontal synchronizing 
signal d is separated from the input video signal a by a synchronizing 
separation circuit 4, and in a control circuit 5, a control signal e is 
formed with reference to a signal d. This control signal e will be an 
input signal from the control signal generating circuit 14. 
Since the phase of a frequency modulator 3 is forcibly reset to a certain 
phase by means of the control signal e, a frequency-modulated wave will be 
in the form of a signal f. This signal f is recorded on a recording tape 8 
by a head 7 via a recording amplifier 6. 
During reproduction, a signal reproduced by a head 9 is passed through a 
head amplifier 10 to reach a frequency demodulator 11, where said signal 
will be frequency-demodulated to obtain a regenerated demodulated signal 
g. The signal g here tends to produce a big spike noise at the FM 
discontinuity as shown in FIG. 2 (F). The signal g is time-base expanded 
only t its video signal part in a time-base expansion circuit 12, and then 
outputted to a terminal 13 as a signal h. That is, the noise spike is 
prevented from being transmitted to the terminal 13. 
One embodiment of the frequency modulator 3 is shown in FIG. 3. This 
modulator has an additional transistor Tr1 disposed in the circuit 
thereof, so that when the transistor Tr1 allows the entry of the control 
signal e into its base, the collector of a transistor Tr2 will be forced 
to be grounded for phase resetting. 
The input video signal a may be a luminance signal or a color difference 
signal, or a time-base multiplex signal resulting from the multiplexing of 
the luminance signal with the color difference signal in the described 
embodiment. 
In the drawing, the area t is shown provided right behind the synchronizing 
signal of the input video signal, but the area t may be placed right 
before the synchronizing signal. 
Though the description was made to indicate that the area t is to receive 
the signal c of a certain level, the insertion of any signal other than 
the video signal into said area will never deviate from the scope of the 
present invention; for example, it does not matter if it is, for example, 
a signal produced within the video tape recording, such as a synchronizing 
signal or burst signal for use in the reproduction operation of the VCR. 
Additionally, for bringing the frequency-modulated wave into 
synchronization with a horizontal synchronizing signal to keep a constant 
phase at all times, for example, a single monostablemultivibrator can 
serve within the control circuit 5. 
If the frequency-modulated wave needs to change in phase depending on 1 H 
(H: horizontal sync interval) or each track, the control signal e must be 
slightly changed for some period of time in response to the change of the 
phase, and the control circuit 5 will necessarily have added structures 
accordingly, which, however, will be within the scope of the present 
invention.