A method of measuring a negative voltage using a device including a first transistor and a second transistor is provided. The first transistor is coupled to the second transistor and the negative voltage is supplied to a gate of the second transistor. A plurality of voltages are provided to a source input of the device. For each voltage of the plurality of voltages, whether a first voltage across the first transistor is equivalent to a second voltage across the second transistor is determined, and, when the first voltage across the first transistor is equivalent to the second voltage across the second transistor, the negative voltage is determined by measuring a magnitude of a positive voltage of the device.