Dynamic circuit disguise for microelectronic integrated digital

Details Dynamic circuit disguise for microelectronic integrated digital Dynamic circuit disguise for microelectronic integrated digital

1991-08-09

1993-04-13

Westin, Edward P.

Electrical transmission or interconnection systems

Nonlinear reactor systems

Parametrons

307443, H03K 1716, H03K 1920

Patent

active

052025918

ABSTRACT:
Focussed ion beam (FIB) implants (38,40) are used to set the threshold voltages of metal-oxide-semiconductor field-effect transistors (MOSFETs) in a selected logic gate (34,36) in a microelectronic integrated digital logic circuit (31) such that the direct current (DC) transfer function and logic thresholds are essentially the same as for another logic gate (30,32) which is not altered by FIB implants, but the switching speed is greatly reduced. This causes the altered gate (34,36) to switch in an apparently normal manner when tested under DC or low speed conditions, but to not switch at normal operating speed. The altered or disguised gate (34,36) is thereby always on or always off at the normal operating speed, whereas the unaltered gate (30,32) switches in the normal manner. This impedes attempts at reverse engineering since the circuit (31) operates differently under test and operating conditions, and the true logic functions of the gate (34,36) cannot be determined by known low speed test procedures.

REFERENCES:
patent: 4409434 (1983-10-01), Basset et al.
patent: 4583011 (1986-04-01), Pechar
patent: 4766516 (1988-08-01), Ozdemir et al.
patent: 4922136 (1990-05-01), Ueda
patent: 4952824 (1990-08-01), Kamuro
Patent Abstracts of Japan, vol. 014, No. 463, Oct. 8, 1990, & JP-A-21 88 944 (Sharp K.K.) Jul. 25, 1990 abstract.

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