JPH0525075Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a tracking circuit that delays a playback control signal in a video tape recorder (VTR).

(b) Prior Art During playback in a VTR, a tracking servo is applied to make the playback head faithfully track the recorded video track. For this purpose, a reproduction control signal is supplied to a delay circuit for tracking. An example of such a servo circuit is shown in pages 136 to 141 of "Introduction to Home VTR" (published by Corona Publishing).

The servo circuit of the VTR will be explained based on the configuration shown in FIG. 3, although the configuration is slightly different from that described in the above-mentioned document. In FIG. 1, 1 is a head servo circuit, and 2 is a capstan servo circuit. Head motor 3
The speed of the head FG signal is controlled by converting the FG signal from the head 4 into a voltage by a frequency-voltage conversion circuit 5 and supplying it to the head motor 3 via an adder circuit 6.

The phase of the head motor 3 is controlled so as to be synchronized with the 1/2 frequency divided output of the vertical synchronizing signal of the video signal to be recorded during recording, and with the 30 Hz output of the reference oscillator during reproduction. That is, the signal selected by the changeover switch 7 and the head PG indicating the rotational phase of the head.
The phase comparison circuit 9 compares the phase of the signal with the 1/2 frequency output from the FF8, and the phase error signal is sent to the addition circuit 6.
is applied to. During recording, the selector switch 10 selects the R side, and the control head records a control signal related to the vertical synchronizing signal. The speed of the capstan motor 11 is controlled by applying the output of the capstan FG signal head 12 to the capstan motor 11 via a frequency-voltage conversion circuit 13 and an addition circuit 14. During recording, in order to ensure accurate rotation of the capstan motor, the output of the capstan FG signal frequency divider circuit 15 is selected by the changeover switch 16.
Vertical synchronization signal 1/2 frequency division output and phase comparison circuit 17
This is done by comparing the phases at

During reproduction, the changeover switches 7, 10, and 16 select the P side. Therefore, the rotational phase of the capstan motor 11 is determined by changing the playback control signal to monomultiple 1.
At steps 8 and 19, the phase of the signal delayed by approximately one period is compared with the reference oscillator output to perform phase control. Since the head motor 3 is also phase controlled based on the same reference oscillator output, the phase with the capstan motor is controlled to have a predetermined relationship using the reference oscillator output as a mate. The monomultis 18 and 19 are equipped with respective time constant circuits 20 and 21, and the first
The time constant of the monomulti 18 can be adjusted using a tracking volume VR that is operable from outside the VTR. Similarly, the time constant circuit 21 of the second monomulti 19 can be adjusted by a semi-fixed resistor _R1 , but this semi-fixed resistor _R1 fixes the tracking volume VR at the center click point when adjusting the servo circuit. , the delay time caused by the monomultis 18 and 19 is adjusted to a predetermined value, and thereafter is fixed.

Tracking volume VR, capacitors C ₁ , C ₂ , and semi-fixed resistors that constitute time constant circuits 20 and 21
_R1 had errors in its resistance and capacitance values, so this adjustment was essential.

(c) Problems to be Solved by the Invention As mentioned above, in the configuration generally used in the past, it was necessary to adjust the delay time of the tracking circuit, which was troublesome. The present invention has been devised in view of this point, and provides a tracking circuit that does not require adjustment of delay time.

(d) Means for Solving the Problems In the present invention, a delay circuit whose delay time is controlled by an external control signal is used as a delay circuit for the reproduction control signal. An output voltage from an externally operable tracking volume is applied to the storage means. A switch is provided in association with the tracking volume, and when this switch is operated, the output voltage of the tracking volume is stored in the storage means. The tracking volume output voltage and the storage means output are supplied to a control signal generating means for generating a voltage related to the difference between the two;
This output controls the delay time of the delay circuit.

(e) Operation A switch is operated at a predetermined position of the tracking volume, and the output voltage is memorized. If the tracking volume is not manipulated, the inputs of the control signal generation circuit are equal, the difference is zero, and the delay time of the delay circuit is a predetermined value. During compatible playback, it is necessary to operate the tracking volume, and a control signal is created based on the difference between the output voltage of the tracking volume and the stored voltage, and the delay time is changed. Therefore, the delay time does not change due to an error in the resistance value of the tracking volume or an error in the power supply voltage, and no adjustment is necessary.

(f) Examples Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an embodiment.

In the figure, 30 is an input terminal for a reproduction control signal, 31 is an output terminal for a delayed reproduction control signal, and 33 is a delay circuit whose delay time is controlled by an external control signal. This delay circuit may be configured to include a voltage controlled oscillator whose frequency changes depending on a control signal voltage of a clock signal of a delay element such as a CCD.

Reference numeral 34 is a tracking volume to which a power supply voltage +B is applied to one end and the other end is grounded, for example, and an output voltage 35 is taken out from a movable contact 34a. Tracking volume 34 output voltage 3
5 is applied to the storage means 36 and the control signal generation means 37. The storage means stores the voltage at the input terminal 36a according to the trigger input to the terminal 36b, and outputs the voltage at the output terminal 36.
c. For example, input terminal 36a
A configuration is conceivable in which the voltage is A/D converted and stored in the RAM at the timing of the trigger input, and the A/D converted output of the RAM is used as the stored output.

The trigger signal for the storage means 36 can be one generated by a switch 38 associated with the tracking volume 34. In the illustrated embodiment, the switch 38 is turned on when the tracking volume 34 is at the center click point A, and when the power supply voltage is energized, the switch 38 is turned on.
By moving the tracking volume to the center click point, the output voltage at the center click point is stored.

The control signal generation means 37 generates a control signal voltage 41 related to the difference between the output voltage 35 of the tracking volume 34 and the storage voltage 40 of the storage means 37, and has a configuration in which both voltages 35 and 40 are input. It is conceivable to have a differential amplifier having bipolar outputs and an adder for adding the differential amplifier output and a reference voltage. The delay time of the delay circuit is set so that a predetermined delay time occurs when this reference voltage is applied.

Once a voltage is stored in the storage means, that voltage is always output. When the tracking volume 34 is located at the center click point,
The two inputs to the control signal generating means 37 are equal;
A reference voltage is applied as a control signal. Therefore, the delay time of the delay circuit 33 is a predetermined value regardless of the error in the resistance value of the tracking volume. During compatible playback (when playing back a tape recorded on another VTR), the tracking volume is operated for tracking adjustment, but the stored voltage 40 and the output voltage of the tracking volume 34 A control signal is created according to the difference between the two, and the delay time is controlled to be long or short.

Other methods of triggering the storage means 36 are possible. For example, a configuration using a volume equipped with a push-on or pull-on type switch, or a configuration in which a completely separate switch is provided.
With a configuration in which the output voltage can be stored at points other than the center click point, the control range of the delay time of the reproduction control signal is expanded.

Also, with the circuit shown in Figure 1, there may be a problem with initialization when the power is turned on for the VTR, but this can be solved by configuring a configuration that also applies a signal related to power-on as a trigger signal. . For example, as shown in FIG. 2, the rise of the power supply voltage is delayed by a differentiating circuit 50 and a delay circuit 51, and the stable output voltage of the tracking volume 34 is stored in the storage means. At this time, the tracking volume 34 is not necessarily set at the center click point. Therefore, a switch 52 is provided in the same way as in FIG. 1, so that when the image quality is degraded in the self-recording/playback mode, the center click point can be set again. The switch that turns on at the center click point may be of any type as long as the member that moves with the movable part of the tracking volume (rotary shaft or sliding member) brings two contact points into contact at the center click point. .

(g) Effects of the invention As described above, according to the invention, there is no need to adjust the delay time of the delay circuit for tracking, so the number of work steps is reduced, and defects due to adjustment errors do not occur, making it practical. be.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment, FIG. 2 is a circuit block diagram of a second embodiment, and FIG. 3 is a circuit block diagram of a conventional example. 33... Delay circuit, 34... Tracking volume, 36... Storage means, 37... Control signal generation means, 38... Switch means.

Claims (1)

[Scope of utility model registration request] A delay circuit whose delay time is controlled by an external control signal receives a reproduction control signal as input, a tracking volume to which a power supply voltage is connected, and an output voltage of a movable contact of the tracking volume as input, and a delay circuit whose delay time is controlled by an external control signal. storage means for storing voltage, switch means for creating the trigger signal, and creating a control signal related to the difference between the output voltage and the storage voltage stored in the storage means;
A tracking circuit comprising a control signal generating circuit for controlling the delay circuit.