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AGC Function for Multiplexed Demodulator

IP.com Disclosure Number: IPCOM000101337D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Elliott, PJ: AUTHOR

Abstract

A circuit improvement in disk files employing demodulators that are multiplexed between two servo heads. Costs are reduced by using the same filter/envelope detector for both automatic gain control (AGC) circuits with logic holding de-selected AGC. Card area, component cost and logic pins are reduced.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 94% of the total text.

AGC Function for Multiplexed Demodulator

       A circuit improvement in disk files employing
demodulators that are multiplexed between two servo heads.  Costs are
reduced by using the same filter/envelope detector for both automatic
gain control (AGC) circuits with logic holding de-selected AGC.  Card
area, component cost and logic pins are reduced.

      Disk file designs constantly seek to reduce the cost of the
electronics as well as the card area used.  One way of achieving this
is to share the electronics between two or more functions.  For
example, high performance disk files may have two actuators per disk
stack.  The demodulator can be multiplexed between the two servo
heads, resulting in savings of cost and card area.  As it is
necessary to have a separate AGC for each head to avoid the long
recovery time when switching from one head to the other, an obvious
way of arranging this is shown in Fig. 1.

      The circuit disclosed shows how further reduction in component
count and hence in cost, area and module pins can be achieved.  The
idea is to have the multiplexer BEFORE the filter, so that only one
filter is needed, as shown in Fig. 2.  This operates well because the
AGC for the head that is not selected is held by the gating logic
shown in Fig. 2.  When the heads are switched, the AGC for the first
head is held, while the other head becomes active. If the 'AGC hold'
line is active, then both AGCs are held. As well as saving one set of
fi...