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High-Speed Write Driver for High-Inductance Head

IP.com Disclosure Number: IPCOM000111057D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Sutardja, P: AUTHOR

Abstract

A resonant-mode write driver circuit for high inductance head described and shown in Fig. 1b.

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High-Speed Write Driver for High-Inductance Head

      A resonant-mode write driver circuit for high inductance head
described and shown in Fig. 1b.

      Fig. 1a shows a typical write driver circuit.  Transistors Q1
and Q2 are the driver transistors.  L is the inductance of the head
and C is the parasitic capacitance of the circuit across L.  The load
resistances RL1 and RL2 are usually maximized under the constraint
that Q1 and Q2 never enter into saturation.  The rise time of the
circuit depends on the values of R, L and C.  In most situation, the
current through L is close to exponential and the rise- time given by
L/2R (i.e., the resonant time constant of the circuit is shorter than
the L/R time constant).  For a typical value of L = 6uH, I = 40mA,
Vcc = 5V and RL1 = RL2 = 40ohm,  this gives an L/2R time constant of
6e-6/80 = 75ns.  As a comparison, typical head/driver combination has
a resonant frequency of about 20MHz, or a resonant time constant
(half cycle) of about 25ns.  Furthermore, it takes several
exponential time constants to reach near steady state value.  Hence,
the circuit can only be operated at less than 2 MHz switching rate.
At higher operating frequency a shift in the magnetic transition
position will occur between blocks written at different frequencies.

      Fig 1b shows modification to the circuit of Fig. 1a to allow
for resonant mode switching.  Diode D1 and D2 are used to enable
resonant mode switching.  At the moment a ...