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Adjustable Write Current Source

IP.com Disclosure Number: IPCOM000039262D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Jaworski, RC: AUTHOR [+3]

Abstract

The DAC Adjustable Write Current Source provides the capability to randomly select eight different values of write current, such that the optimal value of write current is attained for a particular head/disk combination, at a particular radial location. Moreover, the selected write current is within 5% of the specified value. This tolerance value is achieved without the use of costly active laser trimming. The DAC Adjustable Write Current Source provides an accurate write current value by making use of a precision reference that is generated on the electronics card. The reference voltage is applied to the negative inputs of the two operational amplifier of the DAC Adjustable Write Current Source as shown in the figure. Operational amplifier Op2 forms a current source with transistor Q9 and external resistor R21.

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Adjustable Write Current Source

The DAC Adjustable Write Current Source provides the capability to randomly select eight different values of write current, such that the optimal value of write current is attained for a particular head/disk combination, at a particular radial location. Moreover, the selected write current is within 5% of the specified value. This tolerance value is achieved without the use of costly active laser trimming. The DAC Adjustable Write Current Source provides an accurate write current value by making use of a precision reference that is generated on the electronics card. The reference voltage is applied to the negative inputs of the two operational amplifier of the DAC Adjustable Write Current Source as shown in the figure. Operational amplifier Op2 forms a current source with transistor Q9 and external resistor R21. The reference voltage, which is maintained across resistor R21 by the operational amplifier Op2-transistor Q9 loop, sets the current in Q9. This current is environmentally stable and is only a function of the 2.5% precision reference voltage and the 1% resistor tolerance. The current in transistor Q9 is then mirrored by transistor Q10-Q14. This current, known as the base current, is five times the current in transistor Q9. Operational amplifier Op1 and transistor Q1 form another current source that is determined by external resistor R20. This current, known as the step current, is mirrored by transistors Q2-Q8 to produce th...