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Programmable Imbedded Read Bias Current Source for MR Head Preamp

IP.com Disclosure Number: IPCOM000108779D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Kerwin, GJ: AUTHOR [+3]

Abstract

A method is disclosed for providing a source of bias current for magnetoresistive read (MR) head that is internal to the electronics housed in the disk enclosure and is also adjustable via external control. The current source is configured to allow for minimum electronic noise as well as minimum voltage drop across the output circuit elements.

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Programmable Imbedded Read Bias Current Source for MR Head Preamp

       A method is disclosed for providing a source of bias
current for magnetoresistive read (MR) head that is internal to the
electronics housed in the disk enclosure and is also adjustable via
external control.  The current source is configured to allow for
minimum electronic noise as well as minimum voltage drop across the
output circuit elements.

      For this circuit, a precision bandgap voltage and an external
1% resistor are the key components used to generate an accurate value
of output current.  An operational amplifier loop is used to compare
the voltage drop across the external resistor with a fraction of the
bandgap voltage.  The fraction is determined by a resistive voltage
divider on the integrated circuit (IC) chip.  The amplifier's output
adjusts the drive to the final current source transistors until the
voltage across the 1% resistor is equal to the voltage divider's
fraction of the bandgap voltage.  The voltage divider is
programmable, under control of logic inputs, to achieve three
programmable values of output current (see the figure).

      Input NREF is a reference voltage from the bandgap circuit.
Resistors R1 and R2 form the voltage divider for the 'base' value of
read bias current.  PFETs T5 and T6 can be activated to logically
switch resistors R11 and R10 into the divider network to achieve
increments to the voltage divider's output voltage.  Input PMED turns...