JPH02246040A - Servo circuit - Google Patents

Abstract

PURPOSE:To improve servo characteristic by detecting a tracking error by supplying the envelope of a reproducing RF signal and a signal generating cyclical change to a phase demodulation circuit, and performing tracking control. CONSTITUTION:The tracking control is performed by detecting the tracking error by supplying the envelope S11 of the reproducing RF signal and the signals S12 and S13 to generate the cyclical change to the phase demodulation circuit 3 using Hilbert transformation. Therefore, since a higher harmonic generated by synchronous detection can be cancelled at the phase demodulation circuit 3, no low-pass filter is required, which simplifies the constitution of a servo circuit. By detecting the tracking error by supplying the envelope S11 of the reproducing RF signal and the signals S12 and S13 to generate the cyclical change on the scanning position of a magnetic head or tape speed, etc., to the phase demodulation circuit 3, a capstan motor is driven so as to eliminate the tracking error. Thereby, it is possible to eliminate phase rounding by the low-pass filter and to improve the servo characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a servo circuit, and particularly to a servo circuit suitable for tracking control of a VTR.

[Summary of the invention]

In a servo circuit that detects tracking errors and controls tracking, this invention provides tracking by supplying the envelope of a reproduced RF signal and a signal that causes periodic changes to a phase demodulation circuit using Hilbert transform. By detecting errors and controlling tracking,
This is designed to improve servo characteristics.

[Conventional technology]

As a tracking control method for a helical scan type VTR, a method for changing the level of a reproduced RF signal has been proposed, one of which is a so-called dynamic tracking method as shown in FIG.

In the configuration shown in FIG. 3, a low frequency vibration signal S2 of several hundred Hz expressed as (sinω.t) is supplied to the piezoelectric bimorph 41 and the delay circuit 42 via the terminal 40.

When the vibration signal S2 is supplied to the piezoelectric bimorph 41, the magnetic head 43 attached to a rotating drum (not shown) via the piezoelectric bimorph 41 changes the width of the magnetic track by expanding and contracting the piezoelectric bimorph 41 in accordance with the vibration signal S2. It is vibrated (woppling) in the direction.

The reproduction RF signal from the magnetic head 43 is transmitted to the reproduction amplifier 44.
The signal is supplied to the detection circuit 45 via.

The reproduced RF signal is subjected to envelope detection in the detection circuit 45, and this detection output (envelope signal 31 expressed as (sin(ω) is 10(1))) is sent to the bypass filter 4.
6 and is supplied to a multiplication circuit 47.

On the other hand, the vibration signal S2 supplied to the delay circuit 42 is delayed by a predetermined time and then supplied to the multiplication circuit 47.

A multiplication circuit 47 to which the envelope signal S1 and the vibration signal S2 are supplied performs synchronous detection.

That is, sin ω. tXsin(ω. 〇(t))−(1
/2) ・(cos(-〇(t))-cos(2ω. 〇(t)) ) ・-41) The detection output expressed by the above equation (1) is supplied to the low-pass filter 48. be done. In equation (1) expressing the detection output, the second term on the right side (c
os (2ω. = 10(1)) is a harmonic generated by synchronous detection, and this harmonic is removed by the low-pass filter 48. Then, the first term ((1/2
)·cos (−θ(1))) is supplied to the phase compensation circuit 49 as a detection output.

The error component θ(1) corresponds to the tracking error, and this error component θ(1) is output from the phase compensation circuit 49 for preventing oscillation, and is supplied to the capstan motor 51 via the amplifier 50. Ru. The capstan motor 51 is driven so as to make the above-mentioned error component θ(1) zero, that is, to eliminate the tracking error.

[Problem to be solved by the invention]

By the way, in the above-mentioned conventional technology, the low-pass filter 48 is configured to filter harmonics (cos(2) generated by synchronous detection).
ω. However, when the above-mentioned harmonics are close to the servo band, the problem is that the servo characteristics deteriorate due to the phase of the low-pass filter 48. there were.

Therefore, an object of the present invention is to provide a servo circuit that can improve servo characteristics.

[Means to solve the problem]

This invention modulates the reproduced RF signal by periodically changing the scanning position of the magnetic head or the tape speed,
In a servo circuit that detects a tracking error based on this reproduced RF signal and controls tracking, the envelope of the reproduced RF signal and a signal that causes periodic changes are sent to a phase demodulation circuit using Hilbert transform. The configuration is such that tracking is controlled by detecting tracking errors.

[Effect]

A phase demodulation circuit is configured using Hilbert transform.

Since harmonics generated by synchronous detection are canceled by this phase demodulation circuit, a low-pass filter is not required, and the configuration of the servo circuit can be simplified.

A tracking error is detected by supplying the envelope of the reproduced RF signal and a signal that causes periodic changes in the scanning position of the magnetic head or the tape speed, etc. to the above-mentioned phase demodulation circuit, and the tracking error is eliminated. The capstan motor is driven. This eliminates phase distortion caused by the low-pass filter, and improves servo characteristics.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In this embodiment, the servo circuit according to the present invention is applied to a VTR.

In the configuration shown in FIG. 1, an error component θ(
1) is supplied to the detection circuit 1 via the terminal 24.

The reproduced RF signal is subjected to envelope detection in a detection circuit 1, and an envelope signal Sl as a detection output expressed as (sin(ω.t+θ(1))) is supplied to an A/Di conversion circuit 2 and digitized. and is supplied to the phase demodulation circuit 3.

On the other hand, from the signal source 4, a low frequency vibration signal S2 expressed as (sinω.t) is sent to the A/D conversion circuit 5 and the phase shift circuit 6.
, are supplied to the delay circuit 7. The vibration signal S2 is digitized by the A/D conversion circuit 5 and supplied to the phase demodulation circuit 3.

Further, the vibration signal S2 is phase-shifted by (π/2) in the phase shift circuit 6, and the vibration signal S2 is expressed as (cos (ω・1)).
It is considered to be 3. This phase-shifted vibration signal S3 is digitized by the A/D conversion circuit 8 and supplied to the phase demodulation circuit 3.

FIG. 2 shows details of the phase demodulation circuit 3.

An envelope signal 311 formed by digitizing the envelope signal S1 is sent to a multiplication circuit 10 via a terminal 9.
The signals are supplied to the Hilbert transform circuit 11, respectively.

The Hilbert transform circuit 11 changes the phase of the input signal over the entire band (π/2) without changing the gain.
It has the function of phase shifting, and its transfer function is expressed as below, and is symmetrical with respect to the coefficients.

H(Z)-(3/128)+(1/16)Z+(21
/128) Z + (79/12B) Z - (79/12B
)Z −(21/12B)Z −(1/16)Z −(
3/12B)Z On the other hand, a vibration signal 313 formed by digitizing the phase-shifted vibration signal S3 is supplied to the multiplication circuit 10 via the terminal 12.

The envelope signal Sll and the vibration signal 313 are multiplied by the multiplication circuit 10, and (1/2) · (sinθ
(t)+5in (2ω* is 10(1))), a digitized signal S14 is formed, and the adder circuit 1
3.

The vibration signal Sll is converted into (π
/2) is phase-shifted, expressed as (-cos(ω.t+θ(1))), and is converted into a digitized signal 315, which is supplied to the multiplication circuit 14. On the other hand, the vibration signal S2 is digitized and The generated vibration signal S12 is supplied via a terminal 15 to a multiplier circuit 14.

The above-mentioned signal 315 and vibration signal 312 are
4, a digitized signal S16 is formed, which is expressed as (-1/2)・(sin(2ω. 10(t))-sinθ(t)), and is sent to the adder circuit 13. Supplied.

The signal 314 supplied from the multiplication circuit 10 and the multiplication circuit 1
4 is added to the signal 316 supplied from the adder circuit 13, and as a result, it has an error component θ(t) and (sin
θ(t)), only the digitized error signal 317 is taken out from the terminal 16 and sent to the D/A conversion circuit 1.
7 and is converted into an analog signal to form an error signal S7.

In this way, the phase demodulation circuit 3 is configured using the Hilbert transform circuit 11, and the phase demodulation circuit 3 cancels harmonics and can obtain only the error signal S7 having the error component θ(1). This eliminates the need for a low-pass filter, simplifying the configuration. Therefore, it is possible to prevent deterioration of the servo characteristics due to the phase shift of the low-pass filter, and it is possible to improve the servo characteristics.

Error signal S7, vibration signal S2 supplied from delay circuit 7
, a speed error signal Set supplied from a speed error circuit to be described later is added in an addition plane path 18, and a control signal S
cl is formed. This control signal Scl is supplied to the capstan motor 20 via the amplifier 19.

This capstan motor 20 includes a frequency signal generator [
A so-called FG) 21 is installed, and the output from the FG 21 is passed through an amplifier 22 to a speed error circuit 23.
and is compared with a predetermined speed to generate its error signal S
et is supplied to the aforementioned adder circuit 18.

By supplying the above-described control signal Scl to the capstan motor 20, the capstan motor 20 is correctly controlled to a rotational speed that eliminates tracking errors.

Although this embodiment describes an example in which the rotational speed of the capstan motor 20 is changed, the invention is not limited to this. For example, the magnetic head may be moved in the width direction of the magnetic track as in the conventional example. It is also possible to perform wotspring.

〔Effect of the invention〕

According to the servo circuit of the present invention, a phase demodulation circuit is configured using Hilbert transform, and tracking errors are eliminated by supplying the envelope of a reproduced RF signal and a signal that causes periodic changes to the phase demodulation circuit. Since the detection and tracking are controlled, the conventional low-pass filter for removing harmonics is not required, and the configuration can be simplified. Therefore, it is possible to prevent deterioration of the servo characteristics due to the phase shift of the low-pass filter, and it is possible to improve the servo characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing a phase demodulation circuit in one embodiment, and FIG. 3 is a block diagram showing a conventional servo circuit. Explanation of main symbols in the drawings 3: Phase demodulation circuit, 11: Hilbert transform circuit, 20.
51: Capstan motor, 43: Magnetic head, Sl:
Envelope signal, S2, S3: vibration signal, θ(t):
error component. Agent Patent Attorney Masatoshi Sugiura

Claims (1)

[Claims] The reproduction RF signal is modulated by periodically changing the scanning position of the magnetic head or the tape speed.
In a servo circuit that detects a tracking error based on a signal and controls tracking, the above-mentioned regenerative RF
A servo circuit that detects tracking errors and controls tracking by supplying a signal envelope and a signal that causes the above-mentioned periodic changes.