A circuit for generating a signal comprising a first transistor having a drain, a gate and a source. A second transistor having a drain, a source and a gate coupled to the gate of the first transistor to form a current mirror. A current source coupled to the source of the first transistor. A diode-connected transistor having a drain coupled to the source of the second transistor, a source and a gate that forms an output. A variable resistor having a first terminal coupled to the source of diode-connected transistor and a second terminal. A capacitor coupled to the second terminal of the variable resistor.