CXD3018Q/R
§5-12. Brake Circuit
Immediately after a long distance track jump it tends to be hard for the actuator to settle and for the servo to
turn on.
The brake circuit prevents these phenomenon.
In principle, the brake circuit uses the tracking drive as a brake by cutting the unnecessary portions utilizing the
180° offset in the RF envelope and tracking error phase relationship which occurs when the actuator traverses
the track in the radial direction from the inner track to the outer track and vice versa. (See Figs. 5-15 and 5-16.)
Concretely, this operation is achieved by masking the tracking drive using the TRKCNCL signal generated by
loading the MIRR signal at the edge of the TZC (Tracking Zero Cross) signal.
The brake circuit can be turned on and off by D18 of $1. (See Table 5-17.)
In addition, the low frequency for the tracking drive after masking can be boosted. (SFBK1, 2 of $34B)
Outer track → Inner track
Inner track → Outer track
REV FWD
JMP JMP
FWD REV
JMP JMP
Servo ON
Servo ON
TRK
DRV
TRK
DRV
RF
Trace
RF
Trace
MIRR
MIRR
TE
0
TE
0
TZC
Edge
TZC
Edge
TRKCNCL
TRKCNCL
TRK DRV
0
0
(SFBK OFF)
TRK DRV
0
0
(SFBK OFF)
TRK DRV
(SFBK ON)
TRK DRV
(SFBK ON)
SENS
TZC out
SENS
TZC out
Fig. 5-15
Fig. 5-16
Register
name
D23 to D20
Command
D19 to D16
1 0
0
ANTI SHOCK ON
ANTI SHOCK OFF
BRAKE ON
1
0
BRAKE OFF
TRACKING
CONTROL
1
0 0 0 1
0
TRACKING GAIN NORMAL
1
TRACKING GAIN UP
1
TRACKING GAIN UP FILTER SELECT 1
TRACKING GAIN UP FILTER SELECT 2
0
: don't care
Table 5-17
– 97 –
ETC [ ETC ]
