KR20040048250A - A servo control system using a hardwired filter in optical disc drive - Google Patents

Abstract

PURPOSE: A servo control system by using a hardwired filter on an ODD(Optical Disc Drive) is provided to offer the optimized servo control system by making a control filter of relatively lower needs for flexibility while using many parts of an operation volume of a DSP(Digital Signal Processor). CONSTITUTION: A DSP processes a signal by receiving an electric signal matched with the light reflected from an optical disc. A memory stores data and filter coefficients. The hardwired filter performs a periodic calculation and outputs a result by receiving the electric signal matched with the light reflected from the optical disc, and referring to the data and the filter coefficients stored in the memory.

Description

A servo control system using a hardwired filter in optical disc drive}

The present invention relates to a servo control system using a hardwired filter in an optical disk driver.

The servo control system in the optical disk drive has a control system for holding the beam of the optical pickup laser on the disk recording surface, moving the beam spot to the target track, and following the beam spot to the track. In addition, there are various control systems for rotating disks and controlling systems for moving tracks to other desired tracks. Such control is generally handled by a DSP (Digital Signal Processor) and sampling due to the high speed of optical disks. The increase in frequency and the addition of many high-performance algorithms add to the DSP burden.

Fig. 1 is a diagram showing the computational burden of the DSP in the optical disk driver.

As the amount of computation performed on the DSP increases, the servo's performance depends more on the DSP's capabilities, reducing the choice of processor, increasing system clocks, and increasing power consumption.

The present invention solves the above problems and optimizes hardware and software (DSP program) while hardwired a control filter that takes up a large portion of the DSP's computational amount and has a relatively low demand for flexibility. It is an object to provide a servo control system.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the computational burden of DSP in an optical disk driver

2 is a block diagram illustrating a servo control system using a hard wired filter according to the present invention;

3 is a view for explaining the structure of a focus controller and a tracking controller;

4 is a diagram for explaining the structure of a first order IIR filter;

5 is a diagram for explaining a logic implementation of a first order IIR filter;

6 is a view showing a function simulation result of the first order IIR filter;

7 is a view for explaining the structure of a focus servo compensator;

8 is a view for explaining the structure of the spindle servo compensator;

9 is a view for explaining the structure of the Track & Sled & Lens centering servo compensator;

10 is a view for explaining the structure of a general servo compensator;

11 is a view showing an operation sequence of a compensator;

12 is a view for explaining the operation between the memory and the filter contol unit shown in FIG.

13 shows a servo control system of an optical disc drive implemented according to the present invention;

14 shows a board plot of hardwired and software filters for a focusing control filter;

15 is a diagram illustrating focus control and track control using a hardwired filter;

16 is a diagram showing spindle motor control using a hardwired filter;

17 is a view for explaining an area occupied by a hardwired filter;

FIG. 18 is a view comparing a case where only a general DSP is used and a case where a hardwired filter according to the present invention is used together with a DSP.

Servo control system using a hard-wired filter in the optical disk driver according to the present invention for solving the above problems,

A DSP which receives an electrical signal corresponding to the light reflected from the optical disk and performs signal processing; A memory for storing data and filter coefficients; And a hard-wired filter that receives an electrical signal corresponding to the light reflected from the optical disk, and performs periodic calculations with reference to the data and the filter coefficients from the memory.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In order to control the servo, DSP generally uses a focusing compensator for tracking the vibration of the disk, a tracking compensator for tracking the eccentricity of the data track, a lens centering compensator for compensating for the shake of the optical pickup lens, and controlling the rotation of the disk. Periodic controls (e.g. using 176.4Khz interrupts, sampling), and other computational programs such as non-periodic auto-negotiation and focus / track pull point-in-time. This DSP computation burden takes up a lot of periodic calculations (compensation filter) as shown in FIG. And these periodic calculations are usually done by changing the coefficients of the filters without changing the filter structure. Therefore, if these control compensators are not processed by DSP but made into hardware to act as the coprocessor of DSP, DSP operation burden can be reduced.

Figure 2 is a block diagram showing a servo control system using a hard-wired filter according to the present invention. The laser beam in the optical pickup is reflected off the disk, enters the photodiode, is converted into an electrical signal, and enters the RF-amp input. Here, servo control signals such as focus error signal and tracking error signal (Track Error) are generated for servo control. These signals are converted to AD and entered into the servo block through interface logic and glue logic. Et al., 光 デ ィ ス ク 技術, ラ ジ オ 技術, 1988). Based on these digital values, the servo controller is driven. The digital filters used as the servo controller are muxed to use DSP programs and hardwired filter blocks, so that some flexibility is maintained. In the hardwired filter block, the filter control block calls a first-order IIR (Infinite Impulse Response) filter as a functional block and uses the time division. Memory is for using filter coefficients and data.

The filter structures of the focus controller and tracking controller used in the present invention are as shown in FIG. This controller is a structure that can be made by using five or several basic structures of the first-order IIR filter shown in FIG. Thus, only one first-order IIR filter is made of hardware and used several times in a predetermined order. The reason for using the first-order IIR filter as a functional block is the minimum basic structure of the filter that is easy to extend in the optical disk drive controller, and the hardware structure is simplified, so the design is easy.

The system function H (z) (a ₀ = 1, N = 1 (order)) of the first-order IIR filter is expressed by the following Equation 1.

The basic logics used in the hardware implementation of the first-order IIR filter are three 16-bit * 16-bit Q15 format multipliers, two 32-bit + 32-bit Q15 format adders, which are needed to multiply the coefficients with the input data (or delay). In addition, three rounders are required to round 32-bit inputs to 16-bit output, one shifter at the last stage, and a register (or memory) to hold the data (previous value). The logic diagram as described above is shown in FIG.

Internal operation of 1st IIR filter includes 1 clock in read operation that reads data and filter coefficients from memory and puts them in registers, 1 clock in calculation operation until passing through shifter through multiplication and addition, and the calculated data into registers. It is designed to take a total of 3 clocks with 1 clock update operation.

In addition, a total of 7 clocks are required to use the primary filter such as a write operation for writing updated data (registers) into memory, and a 1-clock flag required to indicate the start and end of the filter operation. 6 shows a function simulation result of the above logic.

The types and features of compensators used as hardwired filter are as follows.

① Focus servo compensator

This compensator, which receives the focus error and generates the focus drive signal, configures the filter to meet two sampling rates (176.4Khz and 11.025Khz) as shown in FIG. 7, and reads the filter calculation value from the DSP in the middle. I created a register to help. There is also a mux to select software and hardwired filters, and one IIR filter is inserted into the output to determine the offset (average value) of the Focus Driver signal.

② Spindle servo compensator

As compensator for driving spindle motor, it accepts input of AFC and APC and uses 11.025Khz interrupt.

③ Track & Sled & Lens centering servo compensator

The basic structure of this compensator that receives the track error and generates the track drive signal is the same as the Focus servo compensator. In addition, the tracking drive signal is used as the input of the sled filter to make the drive signal for driving the sled motor, and the lens centering filter. The filter passed through is added to the track drive signal to compensate for the lens.

④ General servo compensator

Extra filter blocks for general use include 176.4Khz sampling second-order IIR filters and 11.025Khz sampling second-order IIR filters.

In the Filter Control block, the order of the control compensators used to control the operation order of the control compensators is as follows. For every interrupt (e.g. 176.4 KHz), General 2nd, Focus 4th, Tracking 4th, Sled 2nd, Offset filter 2nd (Fod 1st, Trd 1st) operate, and every 16 interrupts (11.025 KHz) The secondary, tracking secondary, lens centering secondary, spindle secondary, and general secondary are operated in the order shown in FIG. These operations are determined in the Filter Control block of FIG.

When the clock of the filter is 67 MHz, 380 cycles (67 MHz / 176.4 KHz) are allocated per interrupt, and the filter operation takes a total of 16 orders 112 cycles (7 cycles * 16). If the interrupt (sampling frequency) is raised to a high frequency of 352.8 KHz (190 cycles), the low-speed DSP may not be able to execute all servo programs in the interrupt service routine within a given cycle. In this case, when combined with Hardwiredfilter, it can cope with the high speed optical disk and greatly reduce the burden on DSP.

A synchronous sram memory is used to store the coefficients and data values. In this paper, three bank0 memories (24 words x 16 bits) and four filter coefficients (four) are used to store the input (1) and the delay (2). Four Bank1 memories (48 words x 16 bits) are used for storage. The reason why 3 and 4 are used for each bank memory instead of one is to perform fast operation by reading and writing the memory values in parallel when calculating the filter. The memory words of Bank1 are also larger than Bank0 because they contain filter coefficients for several frequency bands.

The DSP used in the present invention was based on the Teaklite core of DSPG Inc. and used the architecture of the Teaklite-development chip. The components are as follows.

-Teaklite core

-7ns cycle time @ 2.5V @ 0.25u

16bit fixed-point DSP CORE

36-bit ALU

-Downloadable program memory of 10K words

Xram (Data memory) of 512 words

-Yram (Data memory) of 1K words

Bus interface unit (BIU)

-On Chip Emulation Module (OCEM)

-On-Chip TJAM unit-Teaklite's JTAG Activated Mailbox (for OCEM)

-On-Chip Interrupt Control Unit (ICU)

Clock Circuit

User-Defined Registers Interface

13 is an actual optical disk drive servo control system used in the present invention. From the left are Disk Drive Deck, RF Board, and DVD Multi chip. The hardwired filter block is implemented as an actual ASIC and fits inside the chip along with other blocks (DVD Muliti chip: ADC, DAC, DSP, Memory, Data Processing block, PRML, ...).

14 is a Bode plot of Software (DSP) and Hardwired filter for a Focusing Controller filter having a sixth order IIR filter structure at a sampling frequency of 176.4 KHz.

FIG. 15A illustrates a process of operating a hardwired focusing filter in a section in which a focus is made on a recording surface of a disc after finding a control start point by moving an actuator up and down to generate a focus error signal. (b) finds the small eccentricity of the track error signal after focusing control and operates the hardwired tracking filter.

In addition, most of the control compensators such as a sled filter and a spindle filter (Fig. 16) for controlling the rotation of the disk are operated as a hardwired filter. However, speed, distance control and other fault handling and emergency during seek should be controlled by DSP because it is not made by hardware.

The area occupied by the hardwired filter manufactured by the 0.18 μm process is shown in FIG. 17. The IIR1 block corresponding to the engine has three multipliers, which occupy more area than the other blocks. Together with the rest of the control blocks, it will occupy more than 25,000 gates. In addition, three memory areas of 24 words x 16 bits and four words of 48 words x 16 bits are occupied.

FIG. 18 is a diagram showing characteristics of a servo control system using only a DSP and a hardwired filter. Except for the area occupied by the flexibility and hardwired filter block, which are characteristic of hardwired, it has the advantages of low power, high performance and low cost.

In the present invention, a hardwired filter is used for the optimal sharing of hardware and software in the optical disk drive, and it can be used as a coprocessor. As the speed of optical disks and the performance of high performance algorithms increase, more and more high-end DSPs are required, resulting in cost burden and power consumption. In addition, external microcomputers are also integrating the processor into one in terms of chip area and price in an SoC environment coming into the chip. In this case, only one RISC processor functions as a system micom and a DSP, and the most demanding servo's periodic control compensators remain the greatest burden. The use of hardwired filters will reduce the processor's many constraints and provide a broader choice of processors. To solve the shortcomings of fixed filter structure, ASIP (Application Specific Instruction Processor), which includes flexibility at a lower price than general-purpose programmable processor, can be utilized as a general purpose coprocessor of optical disk drive.

Claims (1)

A DSP which receives an electrical signal corresponding to the light reflected from the optical disk and performs signal processing; A memory for storing data and filter coefficients; And And a hardwired filter receiving an electrical signal corresponding to the light reflected from the optical disk and performing periodic calculations with reference to the data and the filter coefficients from the memory. Servo control system.