Current-Mode Phase-Locked Loops with Active Inductors & Transformers

The main function of a PLL is to align up the phase of its input with that of the output of its local oscillator. To speed up the phase-locking process, a frequency detector that senses the frequency difference between the input of the PLL and the output of its local oscillator is often needed. An introduction of PLLs was available in [68] and a detail treatment of the circuit implementation of the building blocks of PLLs was given in [14]. This chapter focuses on current-mode PLLs with active inductors and transformers. The use of active inductors and active transformers in PLLs offers the critical advantages of a significantly reduced silicon area, a large frequency tuning range of the local oscillator subsequently a large acquisition range, tunable loop dynamics, and a fast locking process.

The chapter is organized as the followings : Section 7.1 reviews the fundamentals of PLLs including classifications, loop dynamics, and phase noise. Section 7.2 deals with active inductor current-mode PLLs. Current-mode loop filters with active inductors are introduced. The loop dynamics of types I and II current-mode PLLs are examined and the design trade-offs are investigated. The phase noise of types I and II current-mode PLLs is also investigated in detail. Two current-mode PLLs, one with an active inductor loop filter and an active inductor LC oscillator and the other with an active inductor loop filter but an spiral inductor LC oscillator, are designed and their performance, in particular, phase noise, is compared. Section 7.3 deals with active transformer current-mode PLLs. Current-mode loop filters with active transformers are introduced and the loop dynamics of current-mode PLLs with active transformers are derived. The phase noise of active transformer current-mode PLLs is investigated. The chapter is summarized in Section 7.4.