Some embodiments relate to a level detector, comprising a current mirror including first and second current legs to carry first and second signals, respectively. The first current leg includes a first variable resistor and the second current leg includes a second variable resistor. During a calibration mode, a switching element provides a predetermined reference voltage across first and second control terminals of the first and second variable resistors, respectively. During a non-calibration mode, the switching element decouples the predetermined reference voltage from the first and second control terminals, and provides a signal across the first and second control terminals. Other embodiments are also disclosed.