A phase calibration methodology for accurate modulated measurements

To address the challenge of the phase calibration of modulated RF and microwave signals or the response of a linear or nonlinear system under modulated excitation, a next-generation comb generator is characterized. The latter allows kHz-level modulation tones in addition to the GHz-level RF and microwave tones, while still exhibiting an acceptable power level for each tone. This comb generator includes a PRBS generator, two dividers and a logical “and” operation to trigger the internal pulse generating unit. The pulse generator is characterized using a calibrated sampling oscilloscope. Depending upon the mode of operation this generator could be operated using a plentitude of possible values for every setting (input frequency, divider value, PRBS length). Each setting results in a different amplitude and phase spectrum. In practice it is impossible to characterize this pulse generator and provide a spectral phase dataset for every possible setting of each mode. To address this problem it is investigated if it is feasible to mathematically obtain the complete amplitude and phase spectrum of each possible setting by just using the characterized information of a single pulse. The amplitude and phase characteristic obtained by the measured and predicted spectrum are analyzed and compared. In this paper this technique will be applied to a comb generator operating under divider or PRBS mode.