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# Pulse-Enhanced High Speed Ferrite Head Write Driver

IP.com Disclosure Number: IPCOM000034626D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 68K

IBM

Tang, YS: AUTHOR

## Abstract

A pulse-enhanced driving technique is described which permits substantial writing speed improvement in a ferrite head write driver. Viewing from the write driver, a ferrite head is similar to the RLC circuit shown in Fig. 1. Although this is a simplified model, it reflects the writing speed limitation imposed by the head inductance (Image Omitted) and capacitance. When driving it with a current step from O to Iw the response can be described by where the dot means time derivative. A fundamental limitation of the rising speed of inductor current IL can be easily seen from these equations. Starting from zero state (IL = O, FC = O), the capacitor voltage cannot increase faster than Iw/C. Unfortunately, equation 1 indicates that the inductor current rising speed is proportional to this limited capacitor voltage.

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Pulse-Enhanced High Speed Ferrite Head Write Driver

A pulse-enhanced driving technique is described which permits substantial writing speed improvement in a ferrite head write driver. Viewing from the write driver, a ferrite head is similar to the RLC circuit shown in Fig. 1. Although this is a simplified model, it reflects the writing speed limitation imposed by the head inductance

(Image Omitted)

and capacitance. When driving it with a current step from O to Iw the response can be described by where the dot means time derivative. A fundamental limitation of the rising speed of inductor current IL can be easily seen from these equations. Starting from zero state (IL = O, FC = O), the capacitor voltage cannot increase faster than Iw/C. Unfortunately, equation 1 indicates that the inductor current rising speed is proportional to this limited capacitor voltage. As a result, the slowness of the rising capacitor voltage is a limiting factor to the writing speed. The new driver disclosed here applies extra current during this period to increase the inductor current. The driver circuit uses a voltage source to supply a large current. Since it is desired to obtain a large capacitor voltage to speed up IL, a voltage source VO can be temporarily connected across the inductor to drive it. The voltage source produces a current impulse through the capacitor and sets up the capacitor voltage immediately. When the voltage source is connected, IL increases at the speed VO/L. As soon as IL reaches the desired Iw, the voltage source is momentarily set to zero and disconnected. This leaves the system in a steady state (VC = O and IL = Iw) with the desired write current in the inductor. When VO is increased, the driver approaches the perfect driver. Note that there is no fundamental limitation on this driving technique. A functional diagram of...