Browse Prior Art Database

MOS Current Driver for Light Emitting Diodes

IP.com Disclosure Number: IPCOM000077328D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Schlig, ES: AUTHOR

Abstract

The advantages, including economy, incident the use of metal-oxide silicon (MOS) technology make it a desirable approach to implementation of the selection logic used to control the state of current drivers, employed to drive light-emitting diode arrangements. In order that the current drivers may integrate with the selection logic therefor, the current drivers should also use MOS technology.

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MOS Current Driver for Light Emitting Diodes

The advantages, including economy, incident the use of metal-oxide silicon (MOS) technology make it a desirable approach to implementation of the selection logic used to control the state of current drivers, employed to drive light-emitting diode arrangements.

In order that the current drivers may integrate with the selection logic therefor, the current drivers should also use MOS technology.

The current driver shown in the figure uses on-chip MOS devices for both the switching and current limiting functions. The arrangement shown allows integration of current limiter with switch and selection logic, minimizes chip area and optimizes current tolerance. The current limiting MOS device Q2 is placed closest to ground potential so that its sourced-to-substrate potential, and therefore its threshold voltage, is precisely determined. The gate of Q2 is connected to a fixed potential V(G). Typically, V(G) is the same voltage supply that serves the selection logic circuits, so that the gate-source voltage is precisely determined. Generally, it is desirable that V be fairly large compared to the threshold voltage so as to minimize area. The drain voltage, in a typical design, would be approximately equal to the light-emitting diode forward voltage,
i.e., 1.5 to 2 volts. To conserve area, the device channel dimensions are made minimal, but tolerance improvements may be obtained by using a relatively long channel, say about 0.002...