| 摘要 |
A filter boost preattenuator provides controlled, rapid variable signal preattenuation at the input of a filter to optimally compensate for the absolute gain increase of the filter caused by increasing the high frequency boost level of the filter. The amplitude of the filter output exhibits very little change during boost variations that dynamically occur in applications such as data and servo signal recovery in disk drives. Using the present invention, disk space overhead needed to allow for readjustment of the automatic gain control system of a read/write channel is minimized. In the present invention, the feedforward signal provided from the variable gain boost circuit is applied to a feedback circuit and subtracted from the system input. The feedback forces a drop in the overall gain of the filter that increases with boost gain. Therefore, when the boost gain value is raised, as occurs when a read channel transitions between "data" and "servo" modes in a disk drive, the overall gain of the filter decreases to compensate, reducing the performance load on the automatic gain control circuitry.
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