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Bipolar PNP Improves N-Rich FET Designs

IP.com Disclosure Number: IPCOM000061524D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Montegari, FA: AUTHOR

Abstract

This disclosure proposes the addition of a bipolar PNP emitter follower to a semiconductor device so as to reduce cell size and improve performance of an N-rich field-effect transistor (FET). A portion of a typical N-rich circuit is indicated in Fig. 1. N-rich FET circuits are designed to use a minimum number of PFETs because of the superior performance of NFETs. The PFETs are only used to precharge or set the state of of a latch or logic circuit. This is then changed by turning on one or more NFETs which are larger than the PFET, thus drawing more current to override the PFET. In such a circuit all of the NFETs performing the logic functions 1 must have higher conductance than the PFETs so as to be individually capable of changing the logic state.

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Bipolar PNP Improves N-Rich FET Designs

This disclosure proposes the addition of a bipolar PNP emitter follower to a semiconductor device so as to reduce cell size and improve performance of an N-rich field-effect transistor (FET). A portion of a typical N-rich circuit is indicated in Fig. 1. N-rich FET circuits are designed to use a minimum number of PFETs because of the superior performance of NFETs. The PFETs are only used to precharge or set the state of of a latch or logic circuit. This is then changed by turning on one or more NFETs which are larger than the PFET, thus drawing more current to override the PFET. In such a circuit all of the NFETs performing the logic functions 1 must have higher conductance than the PFETs so as to be individually capable of changing the logic state. The N-rich circuits may be improved with the addition of a bipolar PNP emitter follower between the logic NFETs and the precharged or latch portion of the circuit (Fig. 2). A low impedance path is provided by the bipolar emitter follower to effectively switch the state of the circuit. This is done while allowing minimum size NFETs 2 to be used in all of the logic functions. The concept may also be applied to N-rich cascade FET logic circuits and FET memory latches. The bipolar emitter follower may be of the vertical, non-isolated type with its collector common to the substrate, or of the lateral type. High beta is not necessary since the current gain of even a low beta bipolar is...