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Nonsaturating Transistor Structure

IP.com Disclosure Number: IPCOM000081398D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Bowman, P: AUTHOR [+2]

Abstract

A transistor needs to be overdriven to be turned on quickly. However, overdriving results in saturation of the transistor with a subsequent large turn-off delay. Fig. 1 shows how an inverted transistor Q2 can be used to curb saturation of transistor Q1. With emitter terminal E connected to ground and collector terminal C through a load resistor to a voltage source, Q1 will tend towards saturation when the current into base terminal B is increased. However before transistor Q1 is saturated, transistor Q2 will begin to conduct, as shown, to clamp collector terminal C at a voltage nearly equal to the voltage drop across resistor R.

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Nonsaturating Transistor Structure

A transistor needs to be overdriven to be turned on quickly. However, overdriving results in saturation of the transistor with a subsequent large turn-off delay. Fig. 1 shows how an inverted transistor Q2 can be used to curb saturation of transistor Q1. With emitter terminal E connected to ground and collector terminal C through a load resistor to a voltage source, Q1 will tend towards saturation when the current into base terminal B is increased. However before transistor Q1 is saturated, transistor Q2 will begin to conduct, as shown, to clamp collector terminal C at a voltage nearly equal to the voltage drop across resistor
R.

Fig. 2, and the sectional view of Fig. 3 taken along line III-III of Fig. 2, illustrate a useful structure which can directly replace the normal transistor. The integrated circuit shown is formed in an N-conductivity type epitaxial layer formed over a P-conductivity type substrate. The epitaxial layer, forming a common collector region, has formed therein a generally C-shaped base region of P- conductivity type. Emitter regions E1 and E2 and optional buried subcollector regions SC1 and SC2 complete transistors Q1 and Q2.

Metallization connects emitter region E2 to base region B1 of transistor Q1. Base region B1 is, in turn, connected to base region B2 of transistor Q2 through the base region serving as resistor R, whose resistance will depend on its length, cross section and conductivity. Base terminal B...