Patent attributes
A coefficient indicating the relationship between a measurement voltage of voltage measuring unit and a voltage drop in a drain bias voltage due to drain current is determined based on at least an S parameter of a measuring system and an input impedance of the measuring unit. A voltage drop at the drain is determined from the coefficient. Based on the determined voltage drop, a drain bias voltage actually applied to the drain of an FET is determined. Also, a coefficient for converting the measurement voltage of the measuring unit into a drain current is determined based on at least an S parameter of a measuring system and the input impedance of the voltage measuring unit and an electrical length of the measuring system if necessary. Based on the determined coefficient, a drain current actually flowing in the FET is determined.