Claus Seisenberger

Phase-Error Measurement and Compensation in PLL Frequency Synthesizers for FMCW Sensors—I: Context and Application

The synthesis of linear frequency sweeps or chirps is required, among others, in frequency-modulated continuous-wave radar systems for object position estimation. Low phase and frequency errors in sweeps with high bandwidth are a prerequisite for good accuracy and resolution, but, in certain applications where high measurement rates are desired, the additional demand for short sweep cycles has to be met. Transient phenomena in dynamic synthesizers as well as nonlinear system behavior usually cause unknown phase errors in the system output. For the class of phase-locked-loop (PLL)-based frequency synthesizers, a novel output phase-measurement method and dedicated circuitry are proposed that allow significant reduction of phase errors by adaptive input predistortion. The measurement procedure is implemented within the PLL control circuitry and does not require external equipment. The application of this method to PLL system identification and linearization of extremely short frequency sweeps is shown

Phase-Error Measurement and Compensation in PLL Frequency Synthesizers for FMCW Sensors—II: Theory

Synthesizers for the generation of frequency- or phase-modulated signals are required in communications, sensing, and many other fields and applications. The widespread use of phase-locked loops (PLLs) as major building blocks in current systems requires accurate models and methods for eliminating the influence of statistical and deterministic errors in the synthesized signals. We propose a novel iterative phase-error-measurement and -compensation procedure applicable in PLL-based synthesizers, for which the mathematical background is presented, and a detailed algorithmic description is given in this work. From a mathematical PLL system model and its response to a periodic excitation by the modulating signal, a method for measuring the instantaneous output signal phase and the actual transfer function of the PLL is derived. It is shown how this knowledge can advantageously be used for pre-distorting the synthesizer input signal to eliminate deterministic errors and to obtain an accurate output phase curve.

Frequency-sweep linearization for FMCW sensors with high measurement rate

In certain object surface distance measurement applications where contactless and robust estimates are required, microwave frequency modulated continuous wave sensors are the solution of choice. High linearity of transmitted frequency over time is a prerequisite for accurate results and poses a challenge, if high measurement rates are to be achieved simultaneously. This paper presents a novel method for sweep linearization in phase-locked-loop-based frequency synthesizers by determining the instantaneous output signal phase and error directly within the synthesizer. The proposed method is compared to a conventional voltage predistortion linearization technique.

Modeling and simulation of PLL-based frequency-synthesizers for FMCW radar

Modeling and simulation of phase-locked loops as important building blocks in many of todays radio-frequency circuits has been a topic of research for the past decades. The capability to directly apply frequency-modulation to the generated signal by fractional-N-techniques suggests the use of phase-locked loops for signal generation in frequency-modulated continuous wave radar systems, where a periodic modulation scheme is employed. Common modeling approaches either apply simplifications at an early stage of development, or do not consider the specifics of periodic excitations. In this paper an approach is shown that takes the periodic nature of the input into account, on which a simulation of the periodic steady-state of the system is based. Results from simulation of a radar frequency- sweep generated by a non-linear phase-locked loop are presented.