Functional Decriptions

DS588PP1 - rev 0.4 April 11, 2002

Copyright

© 2002 Cirrus Logic Inc.

www.cirrus.com

6

The channel is controlled by a state machine that automatically starts timing recovery and

deals with defects. This ensures quick recovery from defects and fast data acquisition

after seeks.

The CL-CS3712 contains a versatile digital block that can be used to monitor the ongoing

‘health’ or ‘quality’ of the channel, and that enables accurate equalization calibration to

compensate for wide variations in disc resolution.

Servo Channel

The CL-CS3712 contains an integrated servo system that can control either a CDROM or

a DVD mechanism, with the following features:

• Servo Control Processor (SCP), implementing algorithms designed specifically

for optical disc drives

• Supports dual pick up for CD and DVD applications

• Integrated RF amplifier with Laser Diode Automatic Power Control (LD APC)

• Track counter with velocity estimation

• Multi-function register banks

• External microcontroller interface circuitry

• Programmable Sample Rate Subsystem

Figure 2 shows the CL-CS3712 in a complete servo system. Four control loops can be

processed by this chip: focus, track, sled, spindle. Since the CL-CS3712 contains a

processor, control algorithms and interface circuitry, little external hardware and little

microcontroller intervention is required to implement the servo system.

Pickup/Sensor Interface

The Pickup Interface is the input to the servo control processor (SCP). This circuitry

provides the analog and digital processing needed before the SCP can process the

control signals from the sensors. Since laser diode automatic power control and

reference voltage generation are also provided, the CL-CS3712 can be connected

directly to the pick up electronics without the need for an external RF amplifier.

Servo Control Processor

The SCP does all the processing necessary to control all four servo loops with little

loading of the external microcontroller. The microcontroller sends setup information and

commands to the control system through the microcontroller interface. It can also monitor

key metrics and change control variables to optimize system performance.

All parameter variables and SCP instructions are stored in internal RAM. Since the CL-

CS3712 is a RAM based device, the microcontroller must first initialize these RAMs

before servo operations can begin.

Servo DACs

Control outputs for the sled, focus, and track loops are converted to analog through an

array of three 11-bit DACs. The spindle loop has a pulse width modulated (PWM) output.