JP2701873B2 - Video recording and playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video recording / reproducing apparatus for reproducing a signal periodically recorded on a magnetic tape.

2. Description of the Related Art In recent years, video recording / reproducing apparatuses, particularly video tape recorders (hereinafter abbreviated as VTRs), have become widespread in the consumer field. In particular, the editing work that was conventionally performed when producing programs at broadcast stations, etc., has been
Something that can be done with R has appeared.

The editing operation is generally performed based on a signal (a control signal, hereinafter abbreviated as a CTL signal) in which a signal synchronized with the video signal is periodically recorded on a magnetic tape when the video signal is recorded. Therefore, it is very important to accurately read the CTL signal in order to enhance editing accuracy. Therefore, in the conventional editing VTR, as shown in FIG. 3, in order to accurately read the CTL signal with the magnetic head 31, the CTL head amplifier 12 Are switched by the head amplifier gain switching circuit 13. As a result, CTL signal count errors during slow playback are prevented, and the editing accuracy is improved. Fig. 4 shows the motor speed command and CTL head amplifier 1 at this time.
2 shows the relationship with the gain of 2.

However, in the above-described conventional configuration, the actual magnetic tape traveling speed differs from the target slow reproduction speed of the motor in a transition period when the reproduction speed is switched. Further, the target slow reproduction speed mode of the motor is not set finely. Therefore, every time the gain of the CTL head amplifier 12 is changed, the output of the CTL head amplifier 12 greatly fluctuates. This fluctuation is erroneously read as an actual CTL pulse. There was a problem that it became worse.

In view of the above problems, the present invention performs fine CTL head amplifier gain switching according to the magnetic tape running speed, and always obtains an appropriate CTL head amplifier gain,
It is an object of the present invention to provide a video recording / reproducing apparatus in which output fluctuations caused by switching of a gain of a head amplifier are minimized.

Means for Solving the Problems In order to achieve the above object, a video recording / reproducing apparatus according to the present invention comprises a frequency generator for generating a pulse synchronized with a rotation speed of a motor for running a magnetic tape, and a frequency generator for generating a pulse. A counter circuit that counts the number of pulses within a certain reference clock interval, a magnitude comparison circuit that compares the count value output by the counter circuit with a large number of preset comparison values, and a magnitude comparison circuit. A DC voltage conversion circuit for converting an obtained output into a DC voltage, and a DC voltage for switching a gain of an amplifier for reproducing a signal periodically recorded on the magnetic tape by the DC voltage output from the DC voltage conversion circuit. And a control amplifier circuit.

According to the present invention, the gain switching of the amplifier (CTL amplifier) is finely and finely performed based on the tape running speed by the above-described configuration. As a result, insufficient CTL amplifier gain and excessive gain caused by the CTL amplifier are prevented. Further, a large change in the CTL amplifier output due to the roughness of the CTL amplifier gain switching command is prevented. This eliminates the CTL pulse miscount.

Hereinafter, a video recording and reproducing apparatus according to an embodiment of the present invention will be described.
This will be described with reference to the drawings.

FIG. 1 is a block diagram showing a video recording / reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 11 is a magnetic head, 12 is a frequency generator that generates a pulse synchronized with the rotation speed of a motor that runs a magnetic tape, and 13 is a pulse that is output from the frequency generator 12 within a certain reference clock interval. This is a counter circuit for counting. Reference numeral 14 denotes a magnitude comparison circuit for comparing the count value of the counter circuit 13 with a large number of predetermined comparison values. Also, 15
Is a DC voltage conversion circuit that converts the output obtained by the magnitude comparison circuit 14 into a DC voltage, and 16 is a DC voltage that can switch the gain of an amplifier that amplifies the reproduction output of the magnetic head 11 by the output DC voltage of the DC voltage conversion circuit 15. This is a voltage control amplifier circuit.

Regarding the video recording / reproducing device configured as described above,
Hereinafter, the operation will be described with reference to FIG. 1 and FIG.

First, FIG. 2 shows the DC voltage control amplifier circuit shown in FIG.
This shows the relationship between the gain of 16 and the tape speed. In FIG. 2, the horizontal axis represents the tape speed (the output pulse of the frequency generator 12 within a certain reference clock interval is counted by a counter circuit).
(Count value when counting at 13). The vertical axis represents the gain of the DC voltage control amplifier circuit 16. S ₁ , S ₂ … S on the horizontal axis
_max is shows a comparison value of the magnitude comparison circuit _{14, G 1, G 2 ...} G max of the vertical axis corresponds to the output DC voltage of the DC voltage conversion circuit 15.

As shown in FIG. 2, when the tape speed exceeds a certain speed, that is, when the count value of the output pulse of the frequency generator 12 becomes equal to or more than _Smax within a certain reference clock interval in the counter circuit 13, the DC voltage control amplification is performed. gain of the circuit 16 becomes G _1. Conversely, when the tape speed becomes lower than a certain speed, that is, in the counter circuit 13, the count value of the output pulse of the frequency generator 12 becomes S ₁ within a certain reference clock interval.
When equal to or less than the gain of the DC voltage control amplifier 16 G _max
It works to become. In the range of the pulse count value during that time, the gain changes in a fine stepwise manner according to the number of comparison values in the magnitude comparison circuit 14 as shown in the figure.

As described above, according to the present embodiment, by appropriately setting the gain switching of the amplifier for amplifying the reproduction output of the magnetic head 11 according to the actual traveling speed of the magnetic tape, it is possible to always provide an appropriate gain to the amplifier. In addition, it is possible to minimize the variation in the output of the amplifier that occurs when the gain is switched, and to eliminate the CTL pulse miscount.

Effects of the Invention As described above, according to the present invention, a frequency generator that generates a pulse synchronized with the rotation speed of a motor that runs a magnetic tape, and a pulse generated by the frequency generator is counted within a certain reference clock interval. Counter circuit, a magnitude comparison circuit that compares the count value of the counter circuit with a number of predetermined comparison values, a DC voltage conversion circuit that converts an output obtained by the magnitude comparison circuit into a DC voltage, By providing a DC voltage control amplifier circuit that switches the gain of the amplifier by the output DC voltage of the DC voltage conversion circuit, it is possible to minimize fluctuations that occur when the gain of the amplifier is switched,
Also, an excellent effect that an appropriate gain can always be given can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between a gain of a DC voltage control amplifier circuit in FIG. 1 and a tape speed, and FIG. FIG. 4 is a block diagram of the video recording / reproducing apparatus, and FIG. 4 is a diagram showing the relationship between the gain of the head amplifier and the gain switching command in FIG. 11: magnetic head, 12: frequency generator, 13: counter circuit, 14: size comparison circuit, 15: DC voltage conversion circuit, 16: DC voltage control amplifier circuit.

Claims (1)

(57) [Claims] 1. A frequency generator for generating a pulse synchronized with a rotation speed of a motor for running a magnetic tape, a counter circuit for counting pulses generated by the frequency generator within a certain reference clock interval, and the counter circuit. A magnitude comparison circuit that compares the count value output by the magnitude comparison circuit with a predetermined number of arbitrary comparison values; a DC voltage conversion circuit that converts an output obtained by the magnitude comparison circuit into a DC voltage; A video recording / reproducing apparatus comprising: a DC voltage control amplifier circuit that switches a gain of an amplifier that reproduces a signal periodically recorded on the magnetic tape according to a DC voltage output from a conversion circuit.