Range-Controlled Floating-Gate Transistors: A Unified Solution for Unlocking and Calibrating Analog ICs
Sai Govinda Rao Nimmalapudi, Georgios Volanis, Yichuan Lu, Angelos Antonopoulos, Andrew Marshall and Yiorgos Makris
ECE Department, The University of Texas at Dallas
ABSTRACT
Analog Floating-Gate Transistors (AFGTs) are commonly used to fine-tune the performance of analog integrated circuits (ICs) after fabrication, thereby enabling high yield despite component mismatch and variability in semiconductor manufacturing. In this work, we propose a methodology that leverages such AFGTs to also prevent unauthorized use of analog ICs. Specifically, we introduce a locking mechanism that limits programming of AFGTs to a range which is inadequate for achieving the desired analog performance. Accordingly, our solution entails a two-step unlock-&-calibrate process. In the first step, AFGTs must be programmed through a secret sequence of voltages within that range, called waypoints. Successfully following the waypoints unlocks the ability to program the AFGTs over their entire range. Thereby, in the second step, the typical AFGTbased post-silicon calibration process can be applied to adjust the performance of the IC within its specifications. Protection against brute-force or intelligent attacks attempting to guess the unlocking sequence is ensured through the vast space of possible waypoints in the continuous (analog) domain. Feasibility and effectiveness of the proposed solution is demonstrated and evaluated on an Operational Transconductance Amplifier (OTA). To our knowledge, this is the first solution which leverages the power of analog keys and addresses both unlocking and calibration needs of analog ICs in a unified manner.
