An Interactive Multiple Servo System for an Optical/Digital Drive

Analysis showed that the servo system should have less than 0.4 um dynamic focus error. This accuracy could be guaranteed with a standard high bandwidth second order loop with lead lag compensation and a low frequency integrator. In the electronic design attention has been paid to avoid signal saturation during seeks due to optical crosstalk between the focus and the tracking channel. This crosstalk is discussed in a companion paper.(2) A measurement of the focus loop transfer function can be found in figure 1.