A Simple Optimization Method for Generating High-Purity Amplitude and Phase Modulation

Abstract

We present a simple method for the adjustment of an in-phase (I) and quadrature-phase (Q) Armstrong-type modulator for use as a calibrator in precision noise metrology. The availability of relatively pure levels of both amplitude modulation (AM) and phase modulation (PM) can greatly simplify the optimal alignment and calibration of metrology equipment such as AM and PM noise measurement systems. The phase and amplitude imbalance of the components that constitute an IQ modulator results in an undesired combination of AM and PM. These impairments must be corrected to generate the pure signals required for metrology. Our proposed method corrects for these non-ideal impairments without needing a calibrated IQ demodulator and offers a high-purity AM/PM signal with spurious modulations as low as 1 ppm. We present the calibration procedure and uncertainty analysis of such a modulator when used as a calibrator for a PM and AM noise measurement system.