Dual-loop digital PLL design for adaptive clock recovery

Abstract

Since most digital phase-locked loops (DPLLs) used in digital data transmission receivers require both fast acquisition of input frequency and phase in the beginning and substantial jitter reduction in the steady-state, the DPLL loop bandwidth is preferred to being adjusted accordingly. In this paper, a bandwidth adjusting (adaptive) algorithm is presented, which allow both fast acquisition and significant jitter reduction for each different noise environment and hardware requirement. This algorithm, based on the recursive least squares (RLS) criterion, suggests an optimal sequence of control parameters for a dual-loop DPLL which achieves the fastest initial acquisition time by trying to minimize the jitter variance in any given time instant. The algorithm can be used for carrier recovery or clock recovery in mobile communications, local area networks and disk drives that require a short initial preamble period.