JPH04115721A - Phase synchronization circuit - Google Patents

Abstract

PURPOSE:To attain quick locking to all read data frequencies by devising the circuit such that a loop gain of a PLL circuit is changed attended with a change in a frequency of a read data. CONSTITUTION:A gain switching control section 6 detects a frequency of a current read data and detects a mode by an external mode switching signal and gives a command of gain switching depending on the detected mode and frequency. A gain arithmetic section 3 receives the command to fetch a current phase detection signal and to decide a gain in response to the gain switching command from the control section 6. The phase detection signal and the gain are subject to multiple processing and adds the result of multiplication to the current phase control signal. The result of addition is a control voltage of a VCO 5 via a D/A converter 4. Then a loop gain of a PLL circuit is decided corresponding to the read frequency and quick locking corresponding to all the read frequencies is implemented.

Description

TECHNICAL FIELD The present invention relates to a phase synchronization circuit, and more particularly to a phase synchronization circuit for a magnetic disk drive for reproducing a reference clock synchronized with the frequency of read data from a magnetic disk medium.

Prior art This type of phase-locked circuit (PLL circuit) uses read data from a magnetic disk medium and a VCO (voltage controlled oscillator).
A phase detector detects the phase difference with the oscillation output from the
The VCO is controlled according to the detected output, and the output of this VCO is used as a reference clock.

Note that the detection output of the phase detector is digitized by the ^/D converter and supplied to the arithmetic circuit.

A loop gain is determined by this arithmetic circuit, this gain is multiplied by the digitized phase detection output, and an analog signal corresponding to the multiplication result is obtained by the D/A converter. Then, by this analog signal, the VCO
Digital processing is common.

In the phase synchronization circuit of such a conventional magnetic disk device,
Gain switching is possible depending on the operating mode of the device. That is, gain switching is performed in two modes: at the start of retraction and at the time of stable retraction.

Here, current magnetic disk devices use a method (zone pit record method: ZBR) in which the frequency of writing and reading is changed stepwise in the cylinder direction of the disk medium.
) is inside the shell.

This is a method adopted to improve the recording density of disk media.

In such a magnetic disk drive, it is important to be able to quickly and stably pull in synchronization over a wide frequency range using the same phase synchronization circuit.

However, in the conventional phase-locked circuit, as mentioned above, only two types of gain switching are performed, and this gain switching is performed in two ways, the pull-in start mode and the stable pull-in mode, regardless of the frequency of the read data. It only performs gain switching.

FIG. 5(a) shows the conventional mode change mode for gain switching, where gains 51 and 52 are the characteristics in the pull-in start mode, and gains 53 and 54 are the characteristics in the stable pull-in mode. be.

What should be noted here is that the read data frequency is Fl
, F2, the gain 51 in the pull-in start mode
．． 52 is the same gain (same slope), and the gains 53 and 54 in the stable pull-in mode are also the same gain (same slope).

Therefore, since the gain is the same for all frequencies in a magnetic disk drive in which the data frequency is changed stepwise in the cylinder direction, there is a drawback that the phase synchronization circuit cannot be quickly pulled in for all frequencies. be.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a phase synchronization circuit capable of performing a quick pull-in operation for all read frequencies of a recording medium.

Structure of the Invention According to the present invention, a voltage controlled oscillator, a phase detection means for detecting a phase difference between an output signal of the oscillator and read data from a magnetic disk medium, and a phase detection means for detecting a phase difference between an output signal of the oscillator and read data from a magnetic disk medium; A phase synchronization circuit for a magnetic disk device, comprising a control means for controlling, and using the output signal of the voltage controlled oscillator as a reference clock, the phase synchronization circuit detects the frequency of the read data and controls the output signal according to the frequency. A phase-locked circuit characterized in that it includes a gain control means for controlling the loop gain of the phase-locked circuit is obtained.

Example The present invention will be described in detail below using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The phase of the read data is compared with the transmission output of vC05 in the phase detector 1, and the phase difference is derived as a phase detection signal.

This phase detection signal is digitized by the A/D converter 2 and input to the gain calculation section 3.

In the gain calculation section 3, a gain is determined in response to a gain switching instruction from the gain switching control section 6, and the phase detection signal is amplified according to this gain to be sent to the D/^ converter 4.
applied to.

The phase detection signal converted into an analog signal by the D/A converter 4 becomes a control voltage for the VCO 5, and the oscillation output of the VCO 5 is controlled. This VCO 5 is led out to the outside as a reference clock, and also serves as a single source for the phase detector 1.

The gain switching control section 6 receives read data and a reference frequency signal in addition to the mode switching signal indicating the two modes described above, and issues a gain switching instruction (according to the mode).
(same as conventional), it also provides a gain switching instruction according to the read data frequency.

FIG. 2 is a diagram showing the relationship between the read data frequency and the determined gain, and shows gain changes corresponding to changes in frequency in two modes: the pull-in start mode and the stable pull-in mode.

During stable pull-in, when the frequency changes from Fl to F2, the gain changes from C to D, and at the start of pull-in, the gain changes from C'
It changes from to Do. In both modes, a linear variation and a stepwise variation are shown, and either variation mode may be used.

In order to achieve such a gain change, the gain switching control section 6 operates according to the flow shown in FIG. That is, in step 31, the frequency of the current read data is detected. As methods for detecting this frequency, there are a method of detecting the ratio between the reference frequency and the read data frequency, and a method of detecting the phase difference between the image frequencies. In particular, in the read data pull-in start mode, this is done by detecting the phase difference between the first few pieces of read data and the reference frequency.

In the next step 32, mode detection is performed using a mode switching signal given from the outside, and in the next step 33
Based on the mode and frequency detected in steps 31 and 32 above, a gain switching instruction is given.

Upon receiving this gain switching instruction, the gain calculating section 3 performs the fourth gain switching instruction.
Perform operations according to the flow shown in the figure. In step 41, the current phase detection signal (digital value) is taken in, and in step 42, a gain is determined in accordance with the gain switching instruction from the gain switching control section 6.

In step 43, the phase detection signal and gain are multiplied, and in step 44, this multiplication result is added to the current phase control signal. As shown in step 45, this addition result is used as a new control signal, and is passed through the D converter 4 to the V
This becomes the control voltage for CO5.

By doing this, the loop gain of the PLL circuit will be determined according to the read frequency at that time.
A pull-in operation that quickly responds to all read frequencies can be performed.

FIG. 5(b) shows the mode of gain switching according to the present invention (
This figure corresponds to the conventional example in a). Gain 51°, 5
2 is the characteristic of the pull-in start mode, with a gain of 53° and a gain of 5.
4 is the characteristic in stable retraction mode.

In the present invention, when the read data frequency changes from Fl to F2, the gain 51°52 in the pull-in start mode changes accordingly (the slope is different), and the gain 53" 54 in the stable pull-in mode also changes accordingly. ing.

In the above embodiment, the PL performing digital processing
Although the L circuit is shown, it can be similarly applied to a PLL circuit for analog processing, and the point is that the loop gain of the PLL circuit may be changed in accordance with the read data frequency.

Effects of the Invention As described above, according to the present invention, since the loop gain of the PLL circuit is configured to change as the frequency of read data changes, rapid pull-in operation is possible for all read data frequencies. It has the effect of becoming.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a diagram showing an example of frequency vs. gain change characteristics of the block in Fig. 1, and Fig. 3 is a diagram of the gain switching control section. A flowchart showing the operation,
FIG. 4 is a flowchart showing the operation of the gain calculating section, FIG. 5(a) is a diagram showing the gain characteristics of a conventional phase locked circuit, and FIG. 5(b) is a diagram showing the gain characteristics of the present invention. Explanation of symbols of main parts 1... Phase detector 3... Gain calculation section 5... VCO 6... Gain switching control section

Claims (1)

[Claims] (1) A voltage controlled oscillator, a phase detection means for detecting a phase difference between the output signal of this oscillator and read data from a magnetic disk medium, and a control means for controlling the voltage controlled oscillator according to this phase difference. This is a phase-locked circuit for a magnetic disk drive in which the output signal of the voltage-controlled oscillator is used as a reference clock, and the loop gain of the phase-locked circuit is determined according to the frequency of the read data. A phase synchronized circuit comprising gain control means for controlling the gain.