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Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet
Rev. 02 — 1 June 2005
38 of 69
Philips Semiconductors
TZA1047
Preprocessor IC for CD and DVD rewritable
7.12 ALFA
7.12.1 ALFA measurement circuit for running OPC
A detailed block diagram of ALFA is shown in
Figure 21.
The ALFA block measures the ALFA parameter to produce an error signal for use in the
running-OPC control loop of a phase change media writer. For phase change media, the
laser power incident at the recording layer is calculated, and is derived from the reection
signal (’reection measurement’). Two methods for measuring the ALFA parameter are
implemented. Both methods are selected by bit ALF1/2, and are dened below.
7.12.1.1
Phase change media
The ALFA measurement is either based on central spot detection (bit ALF1/2 = 0) or on
satellite spot detection (bit ALF1/2 = 1). In the former case, sampling during the erase
period of rf-norm takes place using RS in the CANORM block; in the latter case sampling
is implemented in the input circuit.
For phase change media the alfa signal produced is either proportional to ‘P
× R’ or to
‘P
√R’, where P is the optical power and R is the reection. These quantities are measured
in the laser power incident on the recording layer. There are two methods dened.
The rst method for phase change media (bit ALF1/2 = 1) uses the signals from the
satellite spots to measure the disc reection. The reection signal is the satellite sum
signal satsum, normalized to the sampled power signal SLASP. If bit SQRT = 1, a
square-root operation is applied and the result is multiplied by LASP to give signal alfa-pc.
The second method for phase change media (bit ALF1/2 = 0) uses the signal from the
central spot rather than from satellite spots to measure the disc reection. The reection
signal is the sampled rf-signal srf, normalized on the sampled power signal SLASP.
The switching over between sampled signals rf and satsum, as well as the switching of
sampled signal LASP by bit ALF1/2 is implemented in the CANORM circuit.
The relationship between the various signals used to produce the ALFA signal for both
For SQRT = 0:
(5)
Fig 21. ALFA block.
Iref(ALFA)
1/7
alfa-mon
ALFA
001aab189
IAN
LASP
SQRT
INA
SLASP
ALFA
I
AN
I
ref ALFA
()
-------------------------
INA
SLASP
------------------
LASP
×
=