PLL-Based Wideband Frequency Modulator: Two-Point Injection Versus Pre-Emphasis Technique

This paper analyzes and compares two popular methods to widen the modulation bandwidth of a phase-locked loop, i.e., the pre-emphasis and the two-point injection technique. The analysis reveals that both architectures have the same sensitivity to gain errors and nonlinearity in the loop, though, compared with the pre-emphasis, the two-point injection scheme features less sources of error and does not require a phase detector with wide range and tight linearity requirements. The verification of the analysis as well as the comparison of the two modulation techniques is carried out on an accurate time-domain model of a 60-GHz digital phase-locked loop, taken as a case study and used to generate wideband chirp signals for a radar system.