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Programmable Compare Circuit

IP.com Disclosure Number: IPCOM000041107D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Beilstein, KE: AUTHOR [+2]

Abstract

Hot electron threshold shift is used to program a compare circuit which can be used, for instance, to eliminate need for laser fuse blowing to access redundant circuits.

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Programmable Compare Circuit

Hot electron threshold shift is used to program a compare circuit which can be used, for instance, to eliminate need for laser fuse blowing to access redundant circuits.

A programmable compare circuit is shown in the figure wherein hot electrons may be trapped in gate insulation of either transistor T1 or T2 during a programming cycle to cause increased threshold voltage in one transistor. For example, by applying a high voltage VH to line D, then raising and lowering the potential on the write line W, node A is raised to VH, the gates of transistors T1 and T3 are at VH and electrons become trapped in their gate insulation. The electrons are made available by forward biasing a nearby P-N junction that acts as an injector. This diode is only powered during the programming phase. Thus, the latch circuit L is programmed to power on in a preferred state. In this example, wherein the threshold voltage (Vt) of transistors T1 and T3 has been raised by trapping electrons in their gate insulation, transistors T2 and T4 will turn on first during power up, thus bringing node A to ground and node B to VH .

In a compare cycle, line D or D(C) goes to VH and line W remains low. The compare cycle state of node C depends on the state programmed into the latch and the state of data line D and its complement, D(C), as shown in the truth table below.

Node A Node A Line D Line D(C) Node C

During During During During During

Programming Compare Compare Comp...