Table 1.

Summary of multifrequency demodulation estimation methods.

method	tuning	configuration	order	references
lock-in amplifier	low-pass filter	open-loop	specified n	[28,39–41]
coherent demodulator	number of hold cycles	open-loop	specified n	[28,44–47,58]
Kalman filter	Qk	closed-loop	1st	[28,31–32,48,53]
Lyapunov filter	Γ	closed-loop	1st	[28,33,35–36,59]
direct-design method	desired poles	closed-loop	specified n	[37–38]