Fast Automatic Frequency Calibrator Using an Adaptive Frequency Search Algorithm

Abstract

A new adaptive frequency search algorithm (A-FSA) is presented for a fast automatic frequency calibrator in wideband phase-locked loops (PLLs). The proposed A-FSA optimizes the number of clock counts for each frequency comparison cycle, depending on the difference between the target frequency and the PLL output frequency, as opposed to a binary frequency search algorithm (B-FSA), where the frequency search time per cycle is fixed. This eliminates unnecessary clocking times during the frequency comparison process, and thus reduces the total PLL lock time. The additional circuitry needed for A-FSA is only a simple counter controller, thus minimizing hardware overhead. To verify the effectiveness of the proposed algorithm, two wideband PLLs are designed and simulated using a 65-nm CMOS technology: one with B-FSA, and the other with A-FSA. The latter achieves a lock time faster than the former by at least a factor of 2, even under worst case conditions.