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Low Leakage Complementary Transistor Switch Cell

IP.com Disclosure Number: IPCOM000047593D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 79K

Publishing Venue

IBM

Related People

Martin, BW: AUTHOR [+4]

Abstract

The described layout reduces cell leakage currents for improved switching speed. The Complementary Transistor Switch (CTS) cell consists of two cross-coupled half cells formed by a very dense, integrated PNP and NPN, as shown in Fig. 1. The PNP load device has a lateral structure that is very susceptible to the parasitic PNP that is formed with the p+ isolation (ISO) region. The leakage path, shown in Fig. 2, can greatly reduce the switching speed of the PNP load transistor. Fig. 3 depicts the layout of the present cell design. Since the load transistor action occurs between the two horizontal p+ diffusions, one would like to retain the gain of the intended PNP by not affecting the physical base length.

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Low Leakage Complementary Transistor Switch Cell

The described layout reduces cell leakage currents for improved switching speed. The Complementary Transistor Switch (CTS) cell consists of two cross- coupled half cells formed by a very dense, integrated PNP and NPN, as shown in Fig. 1. The PNP load device has a lateral structure that is very susceptible to the parasitic PNP that is formed with the p+ isolation (ISO) region. The leakage path, shown in Fig. 2, can greatly reduce the switching speed of the PNP load transistor. Fig. 3 depicts the layout of the present cell design. Since the load transistor action occurs between the two horizontal p+ diffusions, one would like to retain the gain of the intended PNP by not affecting the physical base length. However, in order to reduce the parasitic gain of the unwanted PNP, the E-mask can be moved inwardly, away from the p+ isolation. This creates a much longer parasitic base-width and corresponding lower leakage. The net result, shown in Fig. 4, is a T-shaped base diffusion that retains the original lateral PNP gain and overall cell size, while significantly reducing isolation leakage currents.

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