JPH0775110B2 - Threaded servo circuit - Google Patents

Description

The present invention relates to a sled servo circuit used in an optical disk device.

[Conventional technology]

FIG. 5 is a block diagram showing a conventional sled servo circuit.

The subtracter 2 subtracts the optical system tracking amount X ₂ from the tracking error amount X ₁ which is an error with respect to the tracking of the light beam, which is input via the input terminal 1, to obtain the optical system / track relative distance variation ΔX (optical system・ The track variation ΔX) is output. The error signal detection circuit 3 detects the optical system / track variation amount ΔX with the detection sensitivity Sd and outputs an error output Sd · ΔX. The analog filter 14 has a gain Gf, receives the error output Sd · ΔX, and outputs the filter output Gf · Sd · ΔX. The control circuit 16 has a sensitivity Sa and has a filter output Gf
Input Sd · ΔX and output optical tracking amount X ₂ .

Here, the optical system tracking amount X ₂ is represented by the equation (1).

X ₂ = SaGfSdΔX (1) Further, the subtracter 2 holds the equation (2).

X ₁ −X ₂ = ΔX (2) Equation (3) is established from Equations (1) and (2).

Since Sa · Gf · Sd >> 1 in the equation (3), the equation (4) is established.

Thus, the optical system / track fluctuation amount ΔX becomes 1 / Sa / Gf / Sd of the tracking error amount X ₁ , but the sensitivity Sa, Sd
Is drastically reduced (-12dB / _DCt ) for input fluctuations above the cutoff frequency determined by the mechanical part, and the phase is delayed. Loop gain S at the frequency where the phase is rotated 180 °
If a ・ Gf ・ Sd is 1 or more, stable operation cannot be expected.
Therefore, the analog filter 14 performs phase compensation.

FIG. 6 is a circuit diagram showing the analog filter 4 of FIG. 5 in detail, and FIGS. 7 (a) and 7 (b) are characteristic diagrams showing the frequency characteristics of the front and rear stages of the analog filter 14, respectively.

Operational amplifier 4 ₃ has a non-inverting input terminal receives a reference voltage through an input terminal 4 _2, an output terminal connected to the output terminal 4 _3. Input terminal 4 ₁ is a resistor 4 ₄ and a capacitor connected in series.
4 ₇ and via are connected to the inverting input of the operational amplifier 4, also via a resistor 4 ₅ is connected to the inverting input terminal. The resistor 4 ₆ and the capacitor 4 ₈ connect the output terminal and the inverting input terminal of the operational amplifier 4, respectively. The output terminal of the operational amplifier 4 ₃ is connected to the output terminal 5 ₆ via the resistor 5 ₁ . resistance
5 ₂ and capacitor 5 ₄ are input terminal 4 ₂ and output terminal 5 _{6 respectively.}
Are connected. The resistor 5 ₃ and the capacitor 5 ₅ are connected in series, and the input terminal 4 ₂ and the output terminal 5 ₆ are connected.

In Fig. ₆ , the resistance values of the resistors 4 ₄ , 4 ₅ , 4, ₆ 5, 5 ₁ , 5 ₂ , 5 ₃ are 4.7KΩ, 22KΩ, 100KΩ, 82KΩ, 47KΩ, 10KΩ, respectively.
Capacitors 4 ₇ , 4 ₈ , 5 ₄ and 5 ₅ have capacitance of 0.0082pF and 100p, respectively.
The frequency characteristics when F, 0.22μF and 3.3μF are shown in Fig. 7 (a) and (b), and are divided into the front stage and the rear stage, but the overall characteristic is the product of the front stage and the rear stage. Is natural.

[Problems to be solved by the invention]

The conventional sled servo circuit described above requires a capacitor with a large capacitance (0.0 several μF to several μF) because the analog filter 14 performs phase compensation, which is unsuitable for integration into a circuit and is low in cost, small in size, and non-integrated. It has the drawback of making coordination difficult.

[Means for solving problems]

The sled servo circuit of the present invention is an optical system / track variation amount that is a difference between a tracking error amount that is a signal indicating a deviation of the optical pickup from the track and an optical system following amount that is a control signal for moving the optical pickup. Error signal detection section that outputs an error output corresponding to the detected optical system / track-to-track variation amount, an A / D converter that A / D converts the error output, and an output of the A / D converter. It has a digital filter for filtering and a control circuit for outputting an optical system tracking amount based on the output of the digital filter.

[Action]

As described above, since the digital filter is used instead of the conventional analog filter, a capacitor having a large capacity is not required, and the integrated circuit can be easily formed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the thread servo circuit of the present invention, FIG. 2 is a block diagram more specifically showing the control circuit 6 portion of FIG. 1, and FIG. 3 is FIG. 1 and FIG. FIG. 4 is a block diagram showing details of the digital filter 5 shown in the figure, and FIG. 4 is a characteristic diagram showing frequency characteristics of the digital filter 5.

The subtracter 2 subtracts the optical system tracking amount X ₂ from the tracking error amount X ₁ input from the input terminal 1 and outputs the optical system / track variation amount ΔX. The error signal detection circuit 3 inputs the optical system / track-to-track variation ΔX, amplifies it, and outputs an error output. Analog / digital converter 4 (hereinafter A /
A D converter 4) inputs the error output and performs A / D conversion.
The digital filter 5 inputs the output of the A / D converter 4 and performs a predetermined position compensation. The control circuit 6 receives the output of the digital filter 5 which is phase-compensated, the PWM converter ₆₁ for performing a pulse width modulation, a driver 6 ₂ for amplifying an output of the PWM converter _61, driven by a driver 6 _{and second} output It is to control the optical system so as to focus the light beam onto a predetermined track on the recording material thin film, which is from the optical pickup control circuit 6 ₃ for outputting an optical system following amount X _2.

The digital filter 5 of this embodiment is a digitalized version of the analog filter 14 shown in FIG. 5, and a calculation formula for setting the circuit of the digital filter 5 will be described.

The S function in the previous stage of the analog filter 14 is given by the equation (1).

Here, a ₁ , a ₂ , b ₁ , b ₂ are constants determined by the resistance and the capacitance element.

Z While frequency the frequency characteristics of the sensitivity of the optical pickup control circuit 6 ₃ controlled becomes 0dB is several KHz, the sampling frequency, the difference method equation (1) because use of 44.1KHz and sufficiently high frequency Can be converted. Also, the formula (1)
Is replaced by a first-order S-function as shown in equation (2) because the frequency used is low.

When this is Z-converted, the equation (3) is obtained.

Where A, B, and G are constants.

The latter stage of the analog filter 14 is a low-pass filter, and when this is approximated by a first-order low-pass filter, the Z function is expressed by the equation (4).

D is a constant.

Therefore, the overall Z function H (Z) of the analog filter 14 is expressed by the equations (3), (4) to (5).

Digital filter 5 based on equation (5)
This will be described with reference to FIGS.

The unit delay element 32 inputs the output of the A / D converter 4 via the input terminal 31 and performs a unit delay Z ^-1 . The multiplier 33 multiplies the output of the unit delay element 32 by a constant A. The adder 34 is A /
The output of the D converter 4 and the output of the multiplier 33 are added. The multiplier 35 multiplies the output of the adder 34 by a constant G. The subtractor 36 subtracts the output of the multiplier 38 from the output of the multiplier 35. The unit delay element 37 inputs the output of the subtractor 36 and performs a unit delay Z ^-1 . The multiplier 38 multiplies the output of the unit delay element 37 by a constant B. The subtractor 39 subtracts the output of the multiplier 42 from the output of the subtractor 36. The overflow detector 40 detects whether the output of the subtractor 39 is overflowing, and outputs the output to the output terminal 43. The unit delay element 41 inputs the output of the overflow detector 40 and performs a unit delay Z ^-1 . Multiplier 42
Multiplies the output of the unit delay element 41 by a constant D.

In this embodiment, the multiplier 35 is arranged in the subsequent stage so that the overflow does not occur when the multiplier 35 multiplies by G, and the overflow detector 40 takes measures against overflow.

In the conventional analog filter 14 having the frequency characteristics shown in FIGS. 7 (a) and 7 (b), the constant of the equation (2) is used.
a ₁ and b ₁ are −5.32 × 10 ³ and −2.59 × 10 ⁴ , respectively. When the Z function is obtained by the difference method with S = (1-Z ^-1 ) / T (T is the sampling period), the coefficients A, B, D and G are -0.8923, -0.6296, -0.997,0.04 respectively. Becomes FIG. 4 shows the frequency characteristic of the digital filter 5 at this time.

〔The invention's effect〕

As described above, the present invention does not require a capacitor having a large capacitance value by processing a signal that was conventionally processed by an analog filter in a sled servo circuit by a digital filter, so that the integrated sled servo circuit is integrated. In addition to facilitating circuitization, it is easy to handle optical discs of different formats, to deal with variations in the finishing precision of the optical discs, etc., and adjustment-free and high quality can be achieved. Further, if the focus servo and the tracking servo are time-divisionally performed by the output of the digital filter of the sled servo circuit of the present invention, the optical disc device can be simplified and downsized, and as a result, the cost of the optical disc device can be reduced. Become.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the thread servo circuit of the present invention, FIG. 2 is a block diagram more specifically showing the control circuit 6 portion of FIG. 1, and FIG. 3 is a digital filter of FIG. 5 in detail, FIG. 4 is a characteristic diagram showing frequency characteristics of the digital filter 5, FIG. 5 is a block diagram showing a conventional example, and FIG. 6 is a conventional example analog filter 14 in FIG. The circuit diagram and FIGS. 7A and 7B are characteristic diagrams showing the frequency characteristics of the front stage and the rear stage of the analog filter 14, respectively. 1 ... Input terminal, 2 ... Subtractor, 3 ... Error signal detection circuit, 4 ... A / D converter, 5 ... Digital filter, 6 ... Control circuit, 6 ₁ ... PWM converter, 6 ₂ ...... Driver, 6 ₃ …… Pickup control circuit.

Claims (1)

[Claims] 1. A sled servo circuit for moving an optical pickup of an optical disc device in a radial direction of the optical disc to access the optical pickup to a predetermined track, which indicates a tracking error amount of a positional deviation from the track of the optical pickup. A subtracter for detecting a difference between the first information and second information indicating an optical system tracking amount for moving the optical pickup to a predetermined track position; and the tracking error extracted as an output of the subtractor. The error signal detection unit that detects the optical system / track variation that is the difference between the optical system tracking amount and the optical system tracking amount, and outputs an error output corresponding to the detected optical system / track variation, and the error output is A A converter for D / D conversion, a digital filter for filtering the output of the A / D converter, and an optical system tracking amount based on the output of the digital filter. Sled servo circuit having a power control circuit.