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Browse Prior Art Database

Precharge for Bootstrap Circuit

IP.com Disclosure Number: IPCOM000089757D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Patel, MP: AUTHOR

Abstract

The figure shows a decode driver which is a bootstrap driver. Referring to the drain decode, Q15 is the bootstrapped load device whose bootstrap capacitor is charged by Q14. In conventional circuits, Q14 is an enhancement-mode field-effect transistor (FET) which is gated by the restore pulse R which is also applied to active FET Q16. When R is up, the gate of Q15 is charged to a voltage equal to the drain voltage V(d) less the threshold voltage of the prior art enhancement-mode FET Q14. This diminished precharge voltage can result in inadequate charging of the bootstrap node.

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Precharge for Bootstrap Circuit

The figure shows a decode driver which is a bootstrap driver. Referring to the drain decode, Q15 is the bootstrapped load device whose bootstrap capacitor is charged by Q14. In conventional circuits, Q14 is an enhancement-mode field- effect transistor (FET) which is gated by the restore pulse R which is also applied to active FET Q16. When R is up, the gate of Q15 is charged to a voltage equal to the drain voltage V(d) less the threshold voltage of the prior art enhancement- mode FET Q14. This diminished precharge voltage can result in inadequate charging of the bootstrap node.

However, using a depletion-mode FET for Q14 allows the full drain voltage V(d) to be applied to the bootstrap node and eliminates the high voltage requirement for the restore pulse R. A depletion-mode FET for Q14 will charge the bootstrap node much faster than will an enhancement-mode FET device.

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