JPH0444620A - Tracking control system envelope detection circuit for video device - Google Patents

Abstract

PURPOSE:To enable exact tracking control with satisfactory responsiveness while preventing the influence of noise by clamping the output of an envelope detection circuit to a prescribed reference potential lower than a detection output corresponding to the timing of generating head switching noise. CONSTITUTION:The outputs of envelope detection circuits 13 and 23 are clamped to the prescribed reference potential lower than the detection outputs corresponding to the timing of generating the head switching noise while driving a switch circuit 2 according to a head switching pulse 7 of a head switching pulse generating circuit 4 and a timing circuit 3. Therefore, during a period when the head switching noise is generated, a capacitor to hold the envelope detection outputs is not affected by charging caused by the noise. As the result, since a voltage is not shifted to a high voltage side by the head switching noise, error is hardly generated in the calculation of a controller side to calculate the tracking control corresponding to the envelope detection outputs. Thus, exact tracking control can be realized with satisfactory responsiveness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a tracking control system envelope detection circuit for a video device. The present invention relates to an improvement in an envelope detection circuit capable of preventing malfunctions in a control system due to head switching noise (or drum switching noise) when a signal is envelope-detected and used as a head tracking control signal.

[Prior art] In a high-fidelity VTR, a video head and an audio head are commonly placed on a rotating cylinder, and the video and audio signals are FM-modulated and recorded on the video track of a tape, and each is demodulated. Then, a video signal is obtained and an H audio signal is obtained. Then, envelope detection is performed on the reproduced FM video signal and FM audio signal, and head tracking control is performed using this envelope detection signal.

[Problem to be solved] A controller for tracking control in this type of tracking control circuit usually performs tracking control using a signal obtained by envelope detection of an FM audio signal and a signal obtained by envelope detection of an FM video signal. However, the noise of the head switching pulse that is performed depending on the number of heads is superimposed on the envelope detection output, and moreover, it appears on the side that charges the capacitor for holding the detection output voltage, so this causes a large difference in the detection output value. This causes a peak, which affects the tracking control calculation result on the controller side and becomes a cause of tracking errors.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the prior art, and to provide a tracking control system envelope detection circuit for a video device that can prevent malfunctions caused by head switching noise.

[Means for Solving the Problems] A feature of the envelope detection circuit of the present invention for achieving such an object is that a voltage is set between the output signal of the envelope detection circuit and a line having a reference potential lower than this output signal. In response to the inserted switch circuit and the head switching signal, this switch circuit is turned on for a predetermined period according to the head switching timing.
The predetermined period is set to a period that does not affect the detection output as a signal for tracking control.

[Function] In this way, the output of the envelope detection circuit is clamped to a predetermined reference potential lower than the detection output in accordance with the timing when head switching noise occurs, so that During this period, the capacitor holding the envelope detection output is not affected by the charging caused by the noise.

As a result, since the voltage does not shift to the higher side due to head switching noise, errors are less likely to occur in the calculations on the controller side, which performs tracking control calculations according to the envelope detection output, resulting in more responsive and accurate calculations. Tracking control can be achieved.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram mainly showing a tracking control system envelope detection circuit of a video apparatus according to the present invention, and FIG. 2 is an explanatory diagram of its output waveform.

In FIG. 1, reference numeral 10 denotes a tracking control system using an FM audio signal, and the FM audio signal read from the magnetic tape track and reproduced by the audio head 11 is transmitted to an input amplifier (or amplifier + BPF (band pass filter), Envelope detection circuit (DET) via AMP) 12
) added to 13. The detection output of the envelope detection circuit 13 is sent to the subsequent output amplifier (AM) as a tracking control signal.
P) 14, and the output of the output amplifier 14 is sent via an A/D conversion circuit (A/D) 15 to a controller such as the CPU 1B that performs tracking control.

Similarly, 20 is a tracking control system using an FM video signal, and the FM video signal is read from the track of the magnetic tape by the audio head 21 and reproduced.
MP) 22 to an envelope detection circuit (DET) 23. The detection output of the envelope detection circuit 23 is output as a tracking control signal to the subsequent output amplifier (AMP) 24, and similarly, the output of the output amplifier 24 is sent to the CPU 1B via the A/D conversion circuit (A/D) 25. is sent out.

The method of tracking control on the CPU 16 side is, for example, first, the envelope detection signal of the FM audio signal is sampled at multiple points on the video track, and tracking control is performed by comparing the average value and the reference level. Control is performed using both the FM audio signal and the FM video signal, such as similarly sampling the envelope detection signal of the FM video signal and comparing the average value and the reference level to perform tracking control. Various types of control are performed, such as sampling both of them and calculating the average value to perform tracking control.

Here, the envelope detection circuit 13 is composed of a detection circuit 1, a switch circuit 2, and a timing circuit 3, and has an input 13a for receiving a reproduction signal from the head, an input 13b1 for receiving a head switching pulse, and an output 13c. I'm doing it. The envelope detection circuit 23 is also a similar circuit composed of a detection circuit, a switch circuit, and a timing circuit. Their operations are similar, so below, F
The detection circuit 13 of the tracking control system based on the M audio signal will be explained, and the explanation of the configuration and operation of the envelope detection circuit 23 will be omitted.

The detection circuit 1 is a so-called envelope detection circuit consisting of a diode D, a capacitor C1 for holding the detection output voltage, and a resistor R, and its output 13c side is connected to a ground line (GND) 5 via a switch circuit 2. There is.

The switch circuit 2 outputs “0N1” from the timing circuit 3.
The timing circuit 3 is a drive circuit for the switch circuit 2, and is composed of a one-shot circuit that generates a no-phrase response at the rising and falling edges of the input pulse. receives a head switching pulse from the switching pulse generation circuit 4 via the input 13b;
The external device generates a pulse having a predetermined pulse width, the pulse width of which can be set by a capacitor Cs. Note that in order to output a detected signal that does not affect the control side in the subsequent stage, the width of the output pulse of the timing circuit 3 is set to several tens of microseconds here.
It is set to c.

As shown in FIG. 2(b), the head switching pulse 7 generated by the head switching pulse generation circuit 4 changes between a HIGH level (hereinafter referred to as "H") and a L level corresponding to the operating period of the head.
This is a pulse that alternately repeats the OW level (hereinafter referred to as "L") and switches the switch circuit that connects the head corresponding to each period to the recording side circuit when in the recording state and to the playback side circuit when in the playback state. .

Next, to explain the overall operation, as shown in FIG.
In response to the change in "41L", head switching noise 6a is generated at each rise and fall, and is superimposed.

Therefore, when this is detected by the detection circuit 1, the same figure (
At each of the rising and falling timings of the head switching pulse 7 in b), the timing circuit 3
An "ON" pulse 8 (see (C) in the same figure) with a width of sec is generated. During the period in which this pulse 8 is generated, the switch circuit 2 is in the "ON" state, and the output 13 of the detection circuit 1 is
Drop the potential of c to ground level (GND).

As a result, as shown in FIG. 3(d), an output waveform 9 is obtained in which the output of the detection circuit 1 is at the ground potential for about several tens of microseconds during which noise is generated.

In contrast, FIG. 9(e) shows a conventional detection output waveform 9a, and when the head switching noise 5a is superimposed, the detection output waveform 9a corresponds to the charging/discharging time constant of the capacitor C of the envelope detection circuit. The voltage decreases with a certain time constant from a high voltage. Therefore, the period during which the detection output is affected becomes longer. However, as shown in FIG. 4(d), the detected output waveform 9 of this embodiment is several tens of μsees because the charge of the capacitor C holding the detected output waveform 9 is discharged by being grounded during this period. Later, a new switch circuit 2
When it is "OFF", charging operation starts from the ground level.

For this reason, the influence of head switching noise on the envelope detection output waveform 9 is completely eliminated during this period. Moreover,
Since this period is as short as several tens of microseconds, the drop of the envelope detection output waveform 9 to the ground level in such a short period of time has almost no effect on the control operation of the subsequent CPU 1B (controller).

As a result, the influence of noise caused by head switching pulses can be eliminated, detection output errors are almost eliminated, and CPU1B
can accurately perform tracking control calculations.

Furthermore, when the difference between the signal level of the detection output and the noise level of the head switching pulse is large during head switching, the recovery of the detection signal output is faster than in the past. As a result, responsiveness to tracking control becomes faster, and followability of tracking control improves.

Incidentally, since audio FM signals have less head switching noise and signal changes more slowly than video signals, an LPF (low pass filter) with a long time constant is often inserted. However, sometimes large noise is added to the audio FM signal when switching heads, and in such cases it is difficult to eliminate the noise with the LPF. However, such noise can be removed by processing with a timing circuit as in the above embodiment.

Furthermore, the reproduced FM signal often changes significantly when the head is switched if tracking deviation occurs. In this case, when the signal changes from a small signal to a large signal, there is not much problem, but when the signal changes from a small signal to a large signal, it takes a long time to discharge, which causes a calculation error. However, if the voltage is instantly dropped to the ground potential (GND) when switching heads as in the circuit of the embodiment, the detection output can better follow the input signal.

As explained above, in the embodiment, a switch circuit is inserted between the output of the envelope detection circuit and the ground potential.
The connection destination of the switch circuit, including the ground potential, may be any general potential that serves as a reference lower than the normal detection output.

[Effects of the Invention] As can be understood from the above explanation, in the present invention, the output of the envelope detection circuit is clamped to a predetermined reference potential lower than the detection output in accordance with the timing of occurrence of head switching noise. Therefore, during the period in which head switching noise is occurring, the capacitor that holds the envelope detection output is not affected by charging due to the noise.

As a result, since the voltage does not shift to the higher side due to head switching noise, errors are less likely to occur in the calculations on the controller side, which performs tracking control calculations according to the envelope detection output, resulting in more responsive and accurate calculations. Tracking control can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram mainly showing a tracking control system envelope detection circuit of a video apparatus according to the present invention, and FIG. 2 is an explanatory diagram of its output waveform. DESCRIPTION OF SYMBOLS 1... Output side of envelope detection circuit, 2... Switch circuit, 3... Timing circuit, 4... Head switching pulse generation circuit, 5... Playback FM audio signal, 5a... Head Switching noise, 10...Tracking control system using FM audio signal, 1
1... Audio head, 12.22, 14.24... Amplifier, 13.23-.
・Envelope detection circuit, 15.25-A/D conversion circuit, IEi-CPU. 20...Tracking control system using FM video signal, 2
1... Image head.

Claims (1)

[Claims] (1) Envelope detection Equipped with an envelope detection circuit having a capacitor that holds an output voltage, an FM signal recorded on a track is reproduced by a head and detected by the envelope detection circuit, and this output signal is used for tracking control. In a video device used as a signal for head switching, a switch circuit is inserted between the output signal of the envelope detection circuit and a line with a reference potential lower than this output signal, and a switch circuit is inserted between the output signal of the envelope detection circuit and a line with a reference potential lower than this output signal, and It is characterized by comprising a switch drive circuit that turns ON for a predetermined period of time according to the switching timing, and the predetermined period of time is set to a period that does not affect the detection output as a signal for tracking control. Tracking control system envelope detection circuit for video equipment.