External biasing control unit for a reading circuit of an infrared photodetector element, the control unit being able to adopt: a first configuration wherein it sends a first set of biasing signals to a first stage of the reading circuit so that this first stage adopts a first operating mode corresponding to a first biasing mode of the photodetector, in particular a direct injection mode, a second configuration wherein it sends a second set of biasing signals to said first stage, the signals in the second set being designed so that said first stage adopts a second operating mode corresponding to a second biasing mode of the photodetector, in particular a buffer direct injection mode.