An Oscilloscope Correction Method for Vector-Corrected RF Measurements

The transfer characteristics of the RF front-end circuitry of a real-time oscilloscope (RTO) are not only frequency dependent and nonlinear with signal amplitude but also dependent on the voltage range setting of the oscilloscope. A correction table in the frequency domain is proposed to account for the additional gain and delay introduced when switching between different voltage ranges. The table was extracted from the measured data in which a continuous-wave signal source was connected to the oscilloscope ports, whereas the input power, the frequency, and voltage ranges were varied. The importance of the corrections is demonstrated by its use in an RTO-based two-port vector-corrected measurement system. Measurements from the oscilloscope-based system are compared with a vector network analyzer (VNA), leading to less discrepancy in the measured S-parameters of two amplifiers when using the proposed correction technique.