Active tamper detection circuit with bypass detection and method therefor

Abstract

An active tamper detection circuit with bypass detection is provided. A bypass detection circuit is coupled to an active mesh loop. The bypass detector includes a voltage comparator with a variable hysteresis control circuit and a calibration engine. The bypass detector detects a change in impedance in the mesh when an attacker attempts to bypass the active loop using a wire. As part of a boot-up sequence, the calibration engine runs a hysteresis sweep on the voltage comparator and stores a hysteresis sweep boot-up signature. When bypass protection is enabled, the bypass detector runs a hysteresis sweep of the voltage comparator periodically at a predetermined interval. Each sweep generates a generated signature that is compared to the stored boot-up signature. Any signature mismatch will be signaled as an impedance mismatch, or tamper. The hysteresis step size is also programmable. The calibration engine can make small changes to the boot-up signature to allow for small voltage variations.