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Integrated NPN Transistors With Different Current Gains

IP.com Disclosure Number: IPCOM000042702D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Wong, RC: AUTHOR

Abstract

In many circuit applications, diodes are connected to the base of an NPN transistor. In some cases, the diodes may be integrated into the transistor structure. For example, in the STL circuit (Fig. 1) the input diodes are integrally fabricated with the collector of the output transistor. However, in many integrated circuit structures diodes have to be placed adjacent to the transistor. This may be accomplished by adding an isolated group of diodes next to the transistor layout. The isolation requirement increases the area of the overall layout. Referring to Fig. 2, it is proposed to integrate the diode into the base of a multi-emitter NPN transistor. Figs. 3 and 4 illustrate the layout and structure of the multi-emitter transistor. Let b be the current gain of T1. Let b' be the current gain of TA.

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Integrated NPN Transistors With Different Current Gains

In many circuit applications, diodes are connected to the base of an NPN transistor. In some cases, the diodes may be integrated into the transistor structure. For example, in the STL circuit (Fig. 1) the input diodes are integrally fabricated with the collector of the output transistor. However, in many integrated circuit structures diodes have to be placed adjacent to the transistor. This may be accomplished by adding an isolated group of diodes next to the transistor layout. The isolation requirement increases the area of the overall layout. Referring to Fig. 2, it is proposed to integrate the diode into the base of a multi- emitter NPN transistor. Figs. 3 and 4 illustrate the layout and structure of the multi-emitter transistor. Let b be the current gain of T1. Let b' be the current gain of TA. T1 is a conventional vertical NPN transistor, which is designed for a high b in the forward direction. TA is a transistor which effectively serves as a diode. This may be accomplished by adjusting the emitter diffusion through the E' contact, so that b' << b. With this condition, the transistor action of TA becomes negligible relative to T1. For example, with proper process control, b and b' for transistors T1 and TA may have the following values and relationship:

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Thus, TA will essentially function as a diode connected to the base of T1, as represented in Fig. 5. A further example of an application...