A circuit includes a first transistor, a second transistor and a first resistive load. The first transistor has a first terminal coupled to a first reference voltage terminal, a second terminal coupled to a second reference voltage terminal, and a control terminal coupled to the first reference voltage terminal. The second transistor has a first terminal coupled to the second reference voltage terminal, a second terminal coupled to the first reference voltage terminal and the control terminal of the first transistor, and a control terminal coupled to the second reference voltage terminal and the second terminal of the first transistor. The first transistor further comprises a third terminal coupled to the second reference voltage terminal through the first resistive load.