| 摘要 |
An integrated circuit has an inhomogeneous protective layer or coating over a circuit to be protected, and a sensing circuit (80) arranged to sense a first impedance of a part of the protective coating compared to a reference impedance (CO) located on the integrated circuit. The sensing circuit is able to measure a change in the first impedance, e.g. caused by tampering. The sensing circuit has an amplifier (OTA) having a feedback loop, such that the impedance being sensed is in the feedback loop. The sensing circuit can be incorporated in an oscillator circuit (OTA, Comp) so that the frequency depends on the impedance. Where the impedance is a capacitance, sensing electrodes adjacent to the protective layer or coating, form the capacitance. The electrodes can be arranged as selectable interdigitated comb structures, so that the protective layer or coating extends in between the teeth of the comb structures. |
