ENGINEERING TRIPOS PART II A and EIST I

EIET LABORATORY ENGINEERING AREA ACTIVITY

Areas 5,6,7 and 8

INVESTIGATION OF THE DESIGN OF CD PLAYERS

SUBTOPIC: MOTOR AND DRIVES

1. INTRODUCTION

The CD player and CD-ROM require several electromechanical motors and actuators to provide some of the primary functions of the unit. The most important functions are controlling the rotation of the disc, the radial tracking of the optical head and the focusing of the laser. The precision required is astounding and these systems must accomodate various problems with the discs, such as the error in the location of the disc in the central clamping mechanism and warpage of the disc.

There is a wide choice of devices suitable for the three main electromechanical actuators. Each requires an interface to the microprocessor and a drive circuit. Feedback control is also essential. For example, in the Philips CD player, the signal is read from the disk by an electro-optical front end, and then after amplification and filtering by front-end electronics, the resulting analogue electronic signal is fed into the SAA7310 decoder IC. This powerful IC demodulates the signal for audio use, in the process extracting bit-timing information used to control the disc rotation speed.

The main aim of this exercise is to understand the operation of the drive circuits, investigate the performance of the actuators and to attempt to understand and explain the factors that influenced the design.

To do this, you will need to draw on a number of sources of information. However, the majority of the work is electronics. You will also have to communicate with the other groups in your session to identify the control signal paths and to understand their importance. You will be able to access some relevant signals inside the CD player.

The main sources of useful information are likely to be: