An electrosurgical system, comprising: a radio frequency output stage configured to output at least one radio frequency waveform; a current sensor coupled to the output stage and configured to output a first differentiated and differential signal corresponding to a current of the at least one radio frequency waveform, the current sensor coupled to a first conditioning circuit configured as a differential amplifier and to integrate the first differentiated signal to output a processed current signal proportional to the current; and a voltage sensor coupled to the output stage and configured to output a second differentiated and differential signal corresponding to a voltage of the at least one radio frequency waveform, the voltage sensor coupled to a second conditioning circuit configured as a differential amplifier and to integrate the second differentiated signal to output a processed voltage signal proportional to the voltage, wherein the first and second conditioning circuits (301, 601) have a matched gain and phase response: wherein the current sensor is a Rogowski coil; wherein the voltage sensor is a capacitive divider; wherein the first conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator; and wherein the second conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator. a radio frequency output stage configured to output at least one radio frequency waveform; a current sensor coupled to the output stage and configured to output a first differentiated and differential signal corresponding to a current of the at least one radio frequency waveform, the current sensor coupled to a first conditioning circuit configured as a differential amplifier and to integrate the first differentiated signal to output a processed current signal proportional to the current; and a voltage sensor coupled to the output stage and configured to output a second differentiated and differential signal corresponding to a voltage of the at least one radio frequency waveform, the voltage sensor coupled to a second conditioning circuit configured as a differential amplifier and to integrate the second differentiated signal to output a processed voltage signal proportional to the voltage, wherein the first and second conditioning circuits (301, 601) have a matched gain and phase response: wherein the current sensor is a Rogowski coil; wherein the voltage sensor is a capacitive divider; wherein the first conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator; and wherein the second conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator. wherein the current sensor is a Rogowski coil; wherein the voltage sensor is a capacitive divider; wherein the first conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator; and wherein the second conditioning circuit comprises a resistor divider, a differential amplifier for converting the differential signal to a single ended signal, a bandpass filter and an integrator.