Next-generation comb generators for accurate modulated measurements

Abstract

When calibrating instrumentation used for measurements at RF and microwave frequencies, periodic pulse-shaped signals are used during phase calibration. However to support measurements of narrowband (a few % of the carrier frequency) signals, the repetition rate of the pulse-shaped signal has to be decreased dramatically from GHz to kHz. The signal-to-noise ratio required to measure such a signal is "more than a challenge" for state-of-the-art instrumentation. A new approach is presented which combines two dividers, a psseudo-random bit sequence (PRBS) generator and a logical "and" operation which triggers a pulse generating unit. These degrees of freedom allow to concentrate energy within a given bandwidth around a specified fundamental frequency and its harmonnics, supporting a frequency spacing in the order of kHz in combination with fundamental frequencies in the order of GHz. Another new "tone selective bit sequence" approach is also explained.