|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: FEEDBACK CONTROL LOOPS
CD players employ a number of control loops which are vital to their function.
This activity will explore the design and operation of the above control loops. The study of the radial and focusing loops will form the main part of the activity. These loops will be investigated with the aid of measurements performed on a control rig.
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:
* Provided when you start doing the activity.
Spend the first period studying how the radial and focusing loops work. The following are some of the principal areas for study.
Use the second and third periods to perform experiments on the rigs to verify and extend your knowledge. You will need to plan out a range of experiments to understand the practical characteristics of the system and the reason for the various design choices.
A CD930 compact disc player has been modified to make the radial and focus tracking errors available for measurement. Also, a summing op-amp circuit has been added to each loop to allow external signals to be injected using a signal generator. The input and output signals at the summing circuits can be measured using an oscilloscope. These facilities allow the experimental identification of the loop transfer functions and various other measurements.
A block diagram representation of the radial and focusing loops is contained in the documentation available.
There is a facility for external control which will not be used in this activity.
M.C. Smith, October 1994
P.R. Palmer, October 2003