A study on MOSFET rectifiers maximum output voltage for RF power harvesting circuits

Radio Frequency (RF) energy harvesting circuits have to harvest energy from very weak sources demanding high sensitivity and high efficiency. In this paper it is presented a study on rectifiers used in RF energy harvesting systems with MOSFET transistors operating in weak-inversion region, where both charge and discharge currents have the same order of magnitude. The study proves that the maximum output voltage of a MOSFET rectifier for very low input voltage is dependent in the first order to the relation between the signal amplitude and thermal voltage (V_T). It is presented a method to calculate the maximum theoretical output voltage in two circuit topologies for input voltages of 10mV, 50mV and 100mV. The circuits are studied for 130nm, 90nm and 45nm CMOS technologies, proving the hypothesized theory that the maximum theoretical output voltage is not a function of the normal transistor parameters (i.e. V_t0, W/L) but instead, the relation between the input voltage amplitude and V_T.