Description Of Circuit - LG GCC-4480B Service Manual

Cd-rw/dvd-rom drive

Hide thumbs Also See for GCC-4480B:

Owner's manual (18 pages)

Table Of Contents

Table of Contents

1. ALPC (Automatic Laser Power Control) Circuit

1-1. Block Diagram

CN 101

VRDC

Optical

Pick-up

HOP-7041T

FVREF

FPDO

VWDC1

Drive

VWDC2

1-2. APC (Automatic Power Control) Block

APC (Automatic Power Control) function in CD-R/RW analog front-end is used for constant power level control

purpose. Based on the accurate power sensor (FMD) in PUH, APC feedback loop maintains constant power level against

laser diode's temperature variation.

There are three power control loops in MT1616, two for CD and one for DVD, which are used with different combination

for different applications. Generally, the first APC loop is used for read-power control. The second APC loop is used for write

(erase) power control for CD-R (CD-RW) disc. And the third APC loop is used for DVD read power control.

Owing to the small signal level in read-power control mode, the first APC loop amplifies (x5/x10/x15/x20) the FMD

signal (FPDO) to enhance the accuracy of read power control. The register VRDCG[1:0] is used to adjust the gain of FMD

signal. The registers RDAC[7:0] and VBDAC[7:0] will set the read power level at the built-in 8-bit DAC (RDAC). The second

APC loop is used for high power control. The built-in 10-bits DAC(WDAC1) is used to set the wanted power level. And the

The following potentiometers (VRDCDAC, VWDC1DAC, and VWDC2DAC) and amplifiers (VRDCDAG, VWDC1DAG,

and WDAC2G) are used to set the wanted levels of VRDCO, VWDC1O, and VWDC2O. Moreover, the input source of the

VWDC2O path can be fed from the output of VWDC1O or directly programmed by the built-in 10-bit DAC (VWDC2DAC).

Moreover, the input signal FPDO (form CD FMD) after low-pass filtering $ amplification (x1 or x2) will send the

MPXOUT2 for monitoring.

Furthermore, the third loop is used for DVD read power control loop. Read power level is adjusted by the RREF voltage

set in the first APC loop.