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解碼器
文件頁(yè)數(shù)： 23/45頁(yè)
文件大小： 224K
代理商： SAA7378GP
Philips Semiconductors
Preliminary specification: Version 1.0
May 1995
23
Digital Servo Processor and Compact Disc Decoder (CD7)
SAA7378GP
8.3.2
The focus control loop contains a digital PID controller which has 5 parameters available to the user. These coefficients
influence the integrating (foc_int), proportional (foc_lead_length, part of foc_parm3) and differentiating (foc_pole_lead, part
of foc_parm1) action of the PID and a digital low pass filter (foc_pole_noise, part of foc_parm2) following the PID. The fifth
coefficient foc_gaininfluences the loop gain.
Focus Position Control Loop
8.3.3
This detector can be influenced by one parameter (CA_drop). The FOK signal will become false and the integrator of the
PID will hold if the CA signal drops below this programmable absolute CA level. When the FOK signal becomes false it is
assumed, initially, to be caused by a black dot.
Drop-out Detection
8.3.4
Whenever FOK is false for longer than about 3ms, it is assumed that the focus point is lost. A fast restart procedure is initiated
which is capable of restarting the focus loop within 200 to 300ms depending on the microprocessor programmed coefficients.
Focus Loss Detection and Fast Restart
8.3.5
The gain of the focus control loop (foc_gain) can be multiplied by a factor of 2 or divided by a factor of 2 during normal
operation. The integrator value of the PID is corrected accordingly. The differentiating (foc_pole_lead) action of the PID can
be switched at the same time as the gain switching is performed.
Focus Loop Gain Switching
8.4
The SAA7378 includes the following focus servo functions:
Radial Servo System
8.4.1
During start-up an automatic adjustment procedure is activated to set the values of the radial error gain (re_gain), offset
(re_offset) and satellite sum gain (sum_gain) for TPI level generation. The initialisation procedure runs in a radial open loop
situation and is
≤
300ms. This start-up time period may coincide with the last part of the motor start up time period.
Automatic gain adjustment: As a result of this initialisation the amplitude of the RE signal is adjusted within
±
10%
around the nominal RE amplitude
Offset adjustment:
The additional offset in RE due to the limited accuracy of the start-up procedure is less
than
±
50nm.
TPI level generation:
The accuracy of the initialisation procedure is such that the duty cycle range of TPI
becomes 0.4 < dutycycle < 0.6 (def. dutycycle: TPI-’high’ / TPI-period).
Level Initialisation
8.4.2
The microprocessor can move the sledge in both directions via the steer sledge command.
Sledge Control
8.4.3
The actuator is controlled using a PID loop filter with user defined coefficients and gain. For stable operation between the
tracks, the S-curve is extended over 0.75 track. Upon request from the microprocessor S-curve extension over 2.25 tracks
is used, automatically changing to access control when exceeding those 2.25 tracks.
Tracking Control
Both modes of S-curve extension make use of a track-count mechanism. In this mode track counting results in an ’automatic
return to zero track’, to avoid major music rhythm disturbances in the audio output for improved shock resistance. The sledge
is continuously controlled using the filtered value of the radial PID output. Alternatively the microprocessor can read the
average voltage on the radial actuator, and provides the sledge with step pulses to reduce power consumption. Filter
coefficients of the continuous sledge control are user presettable.
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