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: DIGITAL TO ANALOG CONVERTER

1. INTRODUCTION

The biggest difference between compact discs and earlier systems such as magnetic tapes and vinyl records is the density of information stored, and the fact that this is digital. The Philips CD930 compact disc player contains a low cost 16-bit digital to analogue converter circuit.

Two digital bit streams are recovered from the disc by the optical reading head and these are converted into the Left and Right analogue signals ready for amplification. An important part of the D/A conversion process is the filtering necessary. In the CD930, the D/A is contained in the SAA7350 integrated circuit and it creates an analogue output by allowing accurately timed pulses to be integrated by a capacitor. In this case the filtering circuit based on the LM833 op-amp eliminates the noise associated with the modulated pulses.

The aim of your investigation should be to understand how the D/A conversion works and to be able to describe the important features of the filter circuit.

The main sources of useful information are likely to be: