JPH0244559A - Video recording and reproducing device - Google Patents

Abstract

PURPOSE:To always obtain suitable gain by providing a frequency generator to generate a pulse, a counter circuit, a size comparing circuit and a direct current voltage converting circuit and switching the gain of an amplifier according to an outputted direct current voltage. CONSTITUTION:When a tape speed goes over a certain speed, namely, when the counted value of an output pulse from a frequency generator 12 is increased in a certain reference clock interval in a counter circuit 13, the gain of a direct current voltage control amplifying circuit 16 is lowered. Reversely, when the tape speed goes to be lower than the certain speed, namely, when the count of the output pulse from the generator 12 is lowered in the certain reference clock interval in the circuit 13, operation is executed so that the gain of the circuit 16 can be increased. In the range of the pulse counted value during the operation, the gain is changed in the shape of fine steps in correspondence to number of a compared value in a size comparing circuit 14. Thus, since the gain switching of an amplifier, which amplifies the reproducing output of a magnetic head 11, is set in correspondence to a traveling speed, the suitable gain can be always given to the amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video recording and reproducing apparatus for reproducing signals periodically recorded on a magnetic tape.

BACKGROUND OF THE INVENTION In recent years, video recording and reproducing devices, particularly video tape recorders (hereinafter abbreviated as VTR), have been widely used in the consumer field. In particular, consumer VTRs have appeared that can perform the editing work that was conventionally done when producing programs at broadcasting stations.

Editing work is generally performed based on a signal (referred to as a control signal, hereinafter abbreviated as CTL signal), which is a signal synchronized with the video signal and periodically recorded on the magnetic tape at the time of recording the video signal. Therefore, it is very important to accurately read this CTL signal in order to improve 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 C' T” I- Change the gain of head amplifier 12 to head amplifier gain switching circuit 1
It was switched by 3. This was intended to prevent CTL signal counting errors during slow playback and improve editing accuracy. FIG. 4 shows the relationship between the motor speed command and the gain of the CTL head amplifier 12 at this time.

Problems to be Solved by the Invention However, in the conventional configuration as described above, the actual magnetic tape running speed and the target slow playback speed of the motor differ during the transition period when switching the playback speed. In addition, the target slow playback speed mode of the motor is not set in detail. Therefore, each time the gain of the CTL head amplifier 12 is changed, the output of the CTL head amplifier 12 changes greatly, and this fluctuation is reflected in the actual CTL head amplifier 12.
Since the CTL pulse is misread as a pulse, the reading of the CTL pulse becomes inaccurate, resulting in poor editing accuracy.

In view of the above-mentioned problems, the present invention performs fine-grained gain switching of the CTL head amplifier depending on the magnetic tape running speed, and always obtains an appropriate gain of the CTL head amplifier. It is an object of the present invention to provide a video recording and reproducing apparatus in which output fluctuations that occur are suppressed to a minimum.

Means for Solving the Problems In order to achieve the above object, the video recording and reproducing apparatus of the present invention includes a frequency generator that generates pulses synchronized with the rotational speed of a motor that runs a magnetic tape, and a counter circuit that counts pulses to be output within a certain reference clock interval, a magnitude comparison circuit that compares the count value outputted by the counter circuit with a large number of arbitrary comparison values set in advance, and a magnitude comparison circuit that A DC voltage conversion circuit converts the obtained output into a DC voltage, and the gain of an amplifier that reproduces the signal periodically recorded on the magnetic tape is determined by the DC:aS voltage output from the DC voltage conversion circuit. It is equipped with a switching DC voltage control amplifier circuit.

Operation The present invention uses the above-described configuration to finely switch the gain of the amplifier (c = rL amplifier) based on the tape running speed, thereby eliminating the conventional CTL amplifier gain switching command given by the speed command of the motor that runs the tape. This prevents insufficient gain or excessive gain of the CTL amplifier, which would otherwise occur due to Furthermore, large fluctuations in CTL and amplifier output due to roughness of the CTL amplifier gain switching command are prevented. This eliminates miscounting of CTL pulses.

Embodiments Hereinafter, video recording and reproducing apparatuses according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a video recording and 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 pulses synchronized with the rotational speed of a motor that runs the magnetic tape, and 13 is a frequency generator that generates pulses output from the frequency generator 12 within a certain reference clock interval. This is a counter circuit that counts. 14 is a magnitude comparison circuit that compares the count value of the counter circuit 13 with a large number of arbitrary comparison values set in advance. Further, 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 conversion circuit that converts the output obtained from the magnitude comparison circuit 14 into a DC voltage.
This is a DC voltage controlled amplifier circuit that can switch the gain of the amplifier that amplifies the reproduced output of 1.

The operation of the video recording and reproducing apparatus configured as described above will be described below with reference to FIGS. 1 and 2.

First, FIG. 2 shows the DC voltage control amplifier circuit 1 in FIG.
6 shows the relationship between the gain of No. 6 and the tape speed. In FIG. 2, the horizontal axis is the tape speed (the counted value when the output pulses of the frequency generator 12 within a certain reference clock interval are counted by the counter circuit 13), and the vertical axis is
This is the gain of the DC voltage control amplifier circuit 16. St on the horizontal axis
, s2...S a&, indicate comparison values of the magnitude comparison circuit 14, and the vertical axis Gl, G2...G,...
E corresponds to the output DC voltage of the DC voltage conversion circuit 15.

As shown in FIG. 2, when the tape speed becomes faster than a certain speed, that is, when the count value of the output pulses of the frequency generator 12 exceeds Sam within a certain reference tarock interval in the counter circuit 13, the DC voltage control is started. Amplifier circuit 1
The gain of 6 is G1. Conversely, when the tape speed becomes slower than a certain speed, that is, in the counter circuit 13,
When the output pulse count of the frequency generator 12 becomes 81 or less within a certain reference clock interval, the gain of the DC voltage control amplifier circuit 16 becomes 01□. In the range of pulse count values in between, 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 below, according to this embodiment, by finely setting the gain switching of the amplifier that amplifies the reproduction output of the magnetic head 11 according to the actual running speed of the magnetic tape, it is possible to always maintain an appropriate gain in the amplifier. I can get it,
Furthermore, it is possible to suppress the output fluctuation of the amplifier that occurs when switching the gain to a minimum, and it is possible to eliminate the miscount of the C'T' L pulse.

Effects of the Invention As described above, the present invention includes a frequency generator that generates pulses synchronized with the rotational speed of a motor that runs a magnetic tape, and a system that counts the pulses generated by the frequency generator within a certain reference clock interval. a counter circuit to
a magnitude comparison circuit that compares the count value of the counter circuit with a large number of preset arbitrary comparison values; a DC voltage conversion circuit that converts the output obtained by the magnitude comparison circuit into a DC voltage; and the DC voltage conversion circuit. By providing a DC voltage control amplifier circuit that switches the gain of the amplifier according to the output DC voltage of the amplifier, it is possible to minimize the fluctuations that occur when switching the gain of the amplifier, and it is possible to always set an appropriate gain. You can get excellent results.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video recording and reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the gain of the DC voltage control amplifier circuit in FIG. 1 and the tape speed, and FIG. FIG. 4, a block diagram of the video recording and reproducing apparatus, is a diagram showing the relationship between the gain of the head amplifier and the gain switching command in FIG. 3. 11... Magnetic head, 12... Frequency generator, 13
... Counter circuit, 14 ... Size comparison circuit, 15
...DC voltage conversion circuit, 16...DC voltage control amplifier circuit. Agent Yoshihiro Morimoto Figure 5, S2 S-Saki Lδ and Figure 4 Figure U finger

Claims (1)

[Claims] 1. A frequency generator that generates pulses synchronized with the rotational speed of a motor that runs the magnetic tape, a counter circuit that counts the pulses generated by the frequency generator within a certain reference clock interval, and the counter circuit. a magnitude comparison circuit that compares the output count value with a large number of preset arbitrary comparison values; a DC voltage conversion circuit that converts the output obtained by the magnitude comparison circuit into a DC voltage; and the DC voltage conversion circuit. A video recording and reproducing apparatus comprising: a DC voltage control amplifier circuit that switches the gain of an amplifier for reproducing signals periodically recorded on the magnetic tape using a DC voltage output from the circuit.