Abstract: Estimation of frequency and amplitude is widely used to accurately trace an unknown sinusoid. Two algorithms, the non-normalized and the normalized frequency estimators, for analysis of sinusoid using 3-dimension adaptive notch filter are presented in this paper. Both of them can achieve accurate estimates of the frequency and the amplitude as well as the tracing of input sinusoid and have circular periodic orbits. The existence and the uniformly asymptotical stability of the integral manifold are verified by Lyapunov stability theorem and the averaging method. The drawback of the non-normalized estimator that the convergence speed is strongly dependent on signal amplitude is amended in the normalized estimator. The effects of the bandwidth parameter and the adaptive gain of estimators on the transient speed and the steady state accuracy as well as the noise characteristics of the algorithms are investigated. The validity of the proposed estimators is verified by simulation results.