參數(shù)資料
型號(hào)： SAA7378GP
廠商： NXP Semiconductors N.V.
英文描述： Single Chip Digital Servo Processor and Compact Disc Decoder
中文描述： 單片機(jī)數(shù)字伺服處理器和光盤(pán)解碼器
文件頁(yè)數(shù)： 22/45頁(yè)
文件大?。?/td> 224K
代理商： SAA7378GP
Philips Semiconductors
Preliminary specification: Version 1.0
May 1995
22
Digital Servo Processor and Compact Disc Decoder (CD7)
SAA7378GP
where the detector set up is assumed as shown in Figure 16.
In the case of single Foucault focusing method, the signal conditioning can be switched under software control such that the
signal processing is as follows:
The error signal, FE
n
, is further processed by a proportional integral and differential (PID) filter section.
A focus OK (FOK) flag is generated by means of the central aperture signal and an adjustable reference level. This signal
is used to provide extra protection for the track-loss (TL) generation, the focus start up procedure and the drop out detection.
The radial or tracking error signal is generated by the satellite detector signals R1 and R2. The radial error signal can be
formulated as follows:
where the index ’s’ indicates the automatic scaling operation which is performed on the radial error signal. This scaling is
necessary to avoid non-optimal dynamic range usage in the digital representation and reduces the radial bandwidth spread.
Furthermore, the radial error signal will be made free from offset during start up of the disc.
The four signals from the central aperture detectors together with the satellite detector signals generate a track position
signal (TPI), which can be formulated as follows:
Where the weighting factor sum_gainis generated internally, by the SAA7378, during initialisation.
8.3
The SAA7378 includes the following focus servo functions:
Focus Servo System
8.3.1
Five initially loaded coefficients influence the start-up behaviour of the focus controller. The automatically generated triangle
voltage can be influenced by 3 parameters; for height (ramp_height) and DC-offset (ramp_offset) of the triangle and its
steepness (ramp_incr).
Focus Start-up
For protection against false focus point detections two parameters are available, which are an absolute level on the CA-
signal (CA_start) and a level on the FE
n
signal (FE_start). When this CA level is reached the FOK signal becomes true.
If this FOK signal is true and the level on the FE
n
signal is reached, the focus PID is enabled to switch on when the next zero
crossing is detected in the FE
n
signal.
Figure 16 Detector Arrangement
Satellite
diode R1
D2
D3
D1
single Foucault
Satellite
diode R2
Satellite
diode R1
D3
D2
D4
D1
Satellite
diode R2
Satellite
diode R1
D3
D4
D2
D1
Satellite
diode R2
astigmatic focus
double Foucault
FE
n
= 2
D1 - D2
D1 + D2
*
RE
s
= (R1 - R2) *re_gain + (R1 - R2)
re_offset
*
TPI = sign [ (D1 + D2 + D3 + D4) - (R1 + R2)
sum_gain]
*
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