CXD3018Q/R
§5-6. AGCNTL (Automatic Gain Control) Function
The AGCNTL function automatically adjusts the filter internal gain in order to obtain the appropriate servo loop
gain. AGCNTL not only copes with the sensitivity variation of the actuator and photo diode, etc., but also
obtains the optimal gain for each disc.
The AGCNTL command is sent when each servo is turned on. During AGCNTL operation, if the upper 8 bits of
the command register are 38 (h), the completion of AGCNTL operation can be confirmed by monitoring the
SENS pin. (See Timing Chart 5-4 and "Description of SENS Signals".)
Setting D9 and D8 of $38 to 1 sets FCS (focus) and TRK (tracking) respectively to AGCNTL operation.
Note) During AGCNTL operation, each servo filter gain must be normal, and the anti-shock circuit (described
hereafter) must be disabled.
XLAT
Max. 11.4µs
SENS
(= AGOK)
AGCNTL completion
Timing Chart 5-4
Coefficient K13 changes for AGF (focus AGCNTL) and coefficients K23 and K07 change for AGT (tracking
AGCNTL) due to AGCNTL.
These coefficients change from 01 to 7F (h), and they must also be set within this range when written externally.
After AGCNTL operation has completed, these coefficient values can be confirmed by reading them out from
the SENS pin with the serial readout function (described hereafter).
AGCNTL related settings
The following settings can be changed with $35, $36 and $37.
FG6 to FG0; AGF convergence gain setting, effective setting range: 00 to 57 (h)
TG6 to TG0; AGT convergence gain setting, effective setting range: 00 to 57 (h)
AGS;
Self-stop on/off
AGJ;
Convergence completion judgment time
Internally generated sine wave amplitude (AGF)
Internally generated sine wave amplitude (AGT)
AGCNTL sensitivity 1 (during rough adjustment)
AGCNTL sensitivity 2 (during fine adjustment)
Rough adjustment on/off
AGGF;
AGGT;
AGV1;
AGV2;
AGHS;
AGHT;
Fine adjustment time
Note) Converging servo loop gain values can be changed with the FG6 to FG0 and TG6 to TG0 setting values.
In addition, these setting values must be within the effective setting range. The default settings aim for
0dB at 1kHz. However, since convergence values vary according to the characteristics of each
constituent element of the servo loop, FG and TG values should be set as necessary.
– 91 –
ETC [ ETC ]
