KEYWORDS: Servomechanisms, Optical discs, Control systems, Digital signal processing, Optical design, Spindles, Video, Sensors, Signal processing, Actuators
Optical disk systems are still widely used in players in consumer electronics and automotive applications, although more
and more audio and video contents are played from other medias such as flash memory and hard disk drive based
devices. There are various architectures with the integrations of audio and video (A/V) decoders and optical disk servo
components to reduced product BOM cost. Some issues are addressed for designing optical disk playing modules into
an audio or video products. Servo implementation including tracking, seeking and rotating control needs to consider the
characteristics of low cost mechanisms and non-ideal disks. When optical disk systems are used in portable or moving
environments, the approaches from servo control side and electronic can be helpful for anti-shock. Special handlings to
defect disks are important to playability.
There are four kinds of semiconductor components in Optical Pickup Units (OPU), i.e. Laser Diode Driver (LDD),
Photo Detect IC (PDIC), Front PDIC (FPD) and High Frequency Modulator (HFM). Two types of LDD described are
direct-drive LDD and write strategy built-in LDD. A PDIC is a light to electrical energy converting device, which
includes photodiodes and transimpedance amplifiers. FPD is a power monitor PDIC. It has some similarity to PDIC but
the requirements differ from PDIC. HFM is used during read by impressing a high frequency current on a DC current to
drive the laser diode to let it emit a discontinue power signal. This paper gives overview of these four ICs and highlights
on key design, application and testing issues.
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