The integrity of integrated circuits (ICs), in particular for detecting malicious add-ons like Hardware Trojans (HTs), have been studied in several recent research papers. The main limit of the proposed techniques so far is that the bias induced by the process variations restrict their efficiency and practicality. Most of those techniques compare two ICs' signatures while trying to get rid of the process variations. In this paper we propose a novel approach which in practice eliminates this limit. We first make the assumption that IC infection is done at a lot level, which is more realistic than models where infections are done on individual circuits. We introduce a variation model for the performance of CMOS structures in real designs which are different from test chips dedicated to the measure of process variations. This model is used to create signatures of lots which are independent of the process variations and is used as a base to define methods allowing to detect HTs and counterfeits in a straightforward way. The model and the methods are validated experimentally on 30 FPGA boards.