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USING ONE SERVO DEMOD CHANNEL TO CONTROL TWO ACTUATORS

IP.com Disclosure Number: IPCOM000013081D
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-12
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

MM YU: AUTHOR [+3]

Abstract

One of the appeals of the dual actuator is that its mechanical cost is only slightly higher than a single actuator, and much less than two separate disk enclosures. There is also an opportunity to reduce the electronics cost by sharing some components between the two actuators. While the pre-amp and power amp for the two VCMs must be duplicated, only one spindle driver is required. Further duplication has been discussed in the art by using only one channel chip and formatter for both VCMs. This invention proposes a cost reduction here of using only one servo demod channel for both VCMs. This is inherently more difficult than using one read/write channel, since servo information is required from both VCMs nearly simultaneously. The first part of the invention is a method of selecting the AE for servo information: The output of both AEs are multiplexed together at the input to the demod channel. The selection of the AE for demod is driven by a programmable timer. The second part is to multiplex the charge storage capacitor on the AGC circuit. Thus when switching from head to head the gain does not need to be reacquired each switch. A different, though more difficult solution is to sum into the VGA gain control a DSP programmable value that accounts for the DC gain offset between heads. This value would need to be stored in the DSP or reacquired whenever a different head pair is selected. The third part is in lieu of the first two: use two AGC circuits, and multiplex the output of them, as in part one.

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USING ONE SERVO DEMOD CHANNEL TO CONTROL TWO ACTUATORS

One of the appeals of the dual actuator is that its mechanical cost is only slightly higher than a single actuator, and much less than two separate disk enclosures. There is also an opportunity to reduce the electronics cost by sharing some components between the two actuators. While the pre-amp and power amp for the two VCMs must be duplicated, only one spindle driver is required. Further duplication has been discussed in the art by using only one channel chip and formatter for both VCMs.

    This invention proposes a cost reduction here of using only one servo demod channel for both VCMs. This is inherently more difficult than using one read/write channel, since servo information is required from both VCMs nearly simultaneously.

   The first part of the invention is a method of selecting the AE for servo information: The output of both AEs are multiplexed together at the input to the demod channel. The selection of the AE for demod is driven by a programmable timer. The second part is to multiplex the charge storage capacitor on the AGC circuit. Thus when switching from head to head the gain does not need to be reacquired each switch. A different, though more difficult solution is to sum into the VGA gain control a DSP programmable value that accounts for the DC gain offset between heads. This value would need to be stored in the DSP or reacquired whenever a different head pair is selected.

   The third part is in lieu of the first two: use two AGC circuits, and multiplex the output of them, as in part one.

   The fourth part of the invention relates to the time skew between sectors on different heads. Because the signals are multiplexed in time, there must be some tim...