In this paper, numerical device simulations are used to get insight into the DC and dynamic behavior of a CMOS metal-semiconductor-metal photodetector, to be used as a mixing device for active pixels based on a differential read-out concept. On the basis of simulation results, a simple electrical macromodel of the photosensor has been defined and implemented in the Cadence package using Spectre AHDL. The proposed macromodel is shown to accurately reproduce the numerical device simulation predictions in all the considered operation modes. (C) 2004 Elsevier Ltd. All rights reserved.