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Filter Select Circuit for Magnetic Disk Read Channel

IP.com Disclosure Number: IPCOM000088931D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 72K

Publishing Venue

IBM

Related People

Lovgren, JL: AUTHOR [+4]

Abstract

The filter select circuit 10 (Figs. 1 and 2) in the read channel for magnetic disk 12 constitutes a second order filter switchable for different filtering characteristics for inner tracks on disk 12 as compared to outer tracks on disk 12, so as to satisfy track (radius) dependent gain and bandwidth requirements for the read channel.

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Filter Select Circuit for Magnetic Disk Read Channel

The filter select circuit 10 (Figs. 1 and 2) in the read channel for magnetic disk 12 constitutes a second order filter switchable for different filtering characteristics for inner tracks on disk 12 as compared to outer tracks on disk 12, so as to satisfy track (radius) dependent gain and bandwidth requirements for the read channel.

The read channel includes magnetic transducer 14 in data transferring relationship with disk 12, playback amplifier 16 connected with transducer 14 to derive signals therefrom, filter select circuit 10 driven from amplifier 16, and detector 18 driven from filter select circuit 10 and providing digital output data on lead 20.

As shown in Fig. 2, filter select circuit 10 has input leads 22 and transducer 14 to derive signals therefrom, filter select circuit 10 driven from amplifier 16, and detector 18 driven from filter select circuit 10 and providing digital output data on lead 20.

As shown in Fig. 2, filter select circuit 10 has input leads 22 and 24 and output leads 26 and 28. Leads 22 and 24 are connected with amplifier 16, and leads 26 and 28 are connected with detector 18. Select circuit 10 comprises four switches SW1, SW2, SW3 and SW4. Switches SW1 and SW2 are controlled by an "intermediate switch" signal on a lead 30, and switches SW3 and SW4 are controlled by an "outer switch" signal on lead 32. Inductances L1 and L2 are in input leads 22 and 24, and capacitor C1 is connected across the outputs of the inductances L1 and L2; therefore, circuit 10 constitutes a second order filter.

Switches SW1, SW2, SW3 and SW4 are of such construction and connections that they effectively ground points A, B, C and D when the switches are closed. Although the ground for the capacitor C1 is not shown, a median point of capacitor C1 is virtually grounded. Therefore, the grounding of points A and B, which takes place simultaneously with a signal being applied to the lead 30, effectively connects capacitors C6 and C7 in series between points E and F so that the combination of capacitors C6 and C7, connected in series, is effectively in parallel with the capacitor C1. Likewise, the application of a signal on lead 32 will close switches SW3 and SW4 effectively, grounding points C and D to, in effect, connect capacitors C8 and C9 in series between points G and H, thus, in effect, providing the combination of these series-connected capacitors between points G and H and in parallel with capacitor C 1.

Signals are provided on leads 30 and 32 by mechanism (not shown) variable with the position of transducer 14 radially of disk 12. This mechanism provides the "outer switch" signal on lead 32 when transducer 14 is between track 00 on the outer margin of disk 12 and track 43 positioned toward the center of rotation of disk 12. The mechanism provides the "intermediate switch" signal on lead 30 when transducer 14 is between tracks 00 and 60, positioned still closer to the cent...