Analysis of millimeter-wave digital frequency modulators for ubiquitous sensors and radars

The need for low-noise, highly-linear, programmable chirp generators makes digital phase-locked loops (DPLLs) an attractive solution for radar sensors. This paper presents a general analysis and comparison of the two main techniques enabling wideband frequency modulation (FM) in PLLs, namely the two-point injection and the pre-emphasis. It is shown that while the two topologies are equivalent in term of mismatch error suppression, the required input range for the time-to-digital converter (TDC) is substantially lower in the two-point injection scheme, thus relaxing the TDC power consumption and linearity.