# US 9,437,219 B1 · Magnetoresistive reader for two-dimensional magnetic recording > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,437,219 B1 - Document ID: US9437219B1 - Status: Granted - Kind: B1 - Application number: 14/850,144 - Filed: 2015-09-10 - Granted: 2016-09-06 - Earliest claimed: 2015-09-10 - Assignees: Avago Technologies General IP (Singapore) Pte. Ltd. - Applicants: Avago Technologies General IP (Singapore) Pte. Ltd. - Inventors: Ross S. Wilson; Scott M. O'Brien; Jeffrey A. Gleason; Jason P. Brenden; Jaydip Bhaumik; David Fitzgerald - Web page: https://patentgrep.com/patent/US9437219B1 ## CPC - G11B 5/09: Digital recording - G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence) - G11B 2005/0018: {by current biasing control or regulation} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract An apparatus for two-dimensional magnetic recording includes a storage medium, an array of magnetoresistive read heads disposed adjacent the storage medium and spaced to read a data track, a number of leads connected to the array of magnetoresistive read heads, and number of bias circuits connected to the array of read heads by the leads. The bias circuits can be configured to independently bias each of the array of read heads with the array of read heads connected in series or in parallel. ## Claims ### Claim 1 An apparatus for two-dimensional magnetic recording, comprising: a storage medium; an array of magnetoresistive read heads disposed adjacent the storage medium and spaced to read a data track; a plurality of leads connected to the array of magnetoresistive read heads; and a plurality of bias circuits connected to the array of magnetoresistive read heads by the plurality of leads, wherein the plurality of bias circuits can be configured to independently bias each of the array of magnetoresistive read heads with the array of magnetoresistive read heads electrically connected in series and with the array of magnetoresistive read heads electrically connected in parallel. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the plurality of bias circuits is configurable for current-bias mode and voltage-bias mode. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the plurality of bias circuits are embodied in a preamplifier circuit. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the plurality of bias circuits comprise a push-pull current source connected to each of the array of magnetoresistive read heads. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the push-pull current sources are each connected across one of the array of magnetoresistive read heads. ### Claim 6 (depends on 4) The apparatus of claim 4, further comprising a plurality of differential bias loop circuits, each connected to one of the push-pull current sources. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the plurality of differential bias loop circuits each comprise an operational transconductance amplifier sensing a voltage across a corresponding one of the read heads and driving a complementary pair of output driving transistors. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the operational transconductance amplifier is configured to sense a voltage across a corresponding one of the read heads when the plurality of bias circuits is configured for a voltage-bias mode. ### Claim 9 (depends on 7) The apparatus of claim 7, wherein the plurality of differential bias loop circuits each further comprise: a second complementary pair of transistors connected around a pair of current sensing resistors; and a reference current source connected across the pair of current sensing resistors, wherein the operational transconductance amplifier is configured to sense a voltage across the pair of current sensing resistors when the plurality of bias circuits is configured for a current-bias mode. ### Claim 10 (depends on 4) The apparatus of claim 4, further comprising a plurality of bias balance loop circuits, each connected to one of the push-pull current sources to balance a push source and a pull source in the push-pull current source. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the plurality of bias balance loop circuits each comprise: a first complementary pair of transistors with a current balance resistor connected between a central node of the first complementary pair of transistors and ground; and an operational transconductance amplifier sensing a voltage across the current balance resistor and driving the first complementary pair of transistors and a second complementary pair of output driving transistors. ### Claim 12 (depends on 1) The apparatus of claim 1, further comprising a plurality of low-noise amplifiers, each connected to one of the magnetoresistive read heads. ### Claim 13 (depends on 12) The apparatus of claim 12, wherein when the plurality of bias circuits are configured to bias the read heads connected in series, each of the low-noise amplifiers are connected across a different one of the series-connected read heads. ### Claim 14 (depends on 12) The apparatus of claim 12, wherein when the plurality of bias circuits are configured to bias the read heads connected in parallel, each of the low-noise amplifiers are connected between a shared pin for the array of magnetoresistive read heads and a dedicated pin for a different one of the parallel-connected read heads. ### Claim 15 (depends on 12) The apparatus of claim 12, further comprising a plurality of nulling feedback loops each connected to one of the low-noise amplifiers to cancel leakage current flow. ### Claim 16 (depends on 12) The apparatus of claim 12, further comprising a common-mode voltage loop connected to each of the low-noise amplifiers to control a common-mode voltage across the array of magnetoresistive read heads. ### Claim 17 A method for accessing a magnetic storage device, comprising: configuring a biasing circuit for an array of read heads according to whether the array of read heads is connected in series or in parallel; configuring the biasing circuit for current-biasing mode or voltage-biasing mode; passing the array of read heads over a data track on a storage medium; and amplifying an analog signal from each read head in the array of read heads in a preamplifier. ### Claim 18 (depends on 17) The method of claim 17, further comprising biasing each read head in the array of read heads using a push-pull current source controlled by a differential bias current loop. ### Claim 19 (depends on 18) The method of claim 18, further comprising balancing a push source and a pull source in each of the push-pull current sources. ### Claim 20 An apparatus for two-dimensional magnetic recording, comprising: a storage medium; an array of magnetoresistive read heads disposed adjacent the storage medium and spaced to read a data track; a plurality of leads connected to the array of magnetoresistive read heads; a plurality of bias circuits connected to the array of magnetoresistive read heads by the plurality of leads, wherein the plurality of bias circuits can be configured to independently bias each of the array of magnetoresistive read heads with the array of magnetoresistive read heads connected in series or in parallel, wherein the plurality of bias circuits comprise a push-pull current source connected to each of the array of magnetoresistive read heads; and a plurality of differential bias loop circuits, each connected to one of the push-pull current sources.