Patent ID: 7702702

Claim:
A signal processing device which computes phase difference between two analog alternating signals through imposing the two analog alternating signals under a predetermined digital signal processing, the signal processing device comprising: a converting unit sampling the two alternating signals with a predetermined period and converting the sampled level values into digital alternating signal data; a filtering unit filtering the two digital alternating signal data generated by the converting unit so as to abstract digital alternating signal data x[k] and y[k], respectively, both having a predetermined frequency, the filtering unit comprising an adaptive digital filter; a differential computing unit computing two digital alternating signal data x′[k] and y′[k] which are differentials of the digital alternating signal data generated by the filtering unit based on Formulae 1-4 below; and a phase difference computing unit computing phase difference φ between the two digital alternating signal data x[k] and y[k] based on Formulae 5 and 6 below using the two digital alternating signal data x[k], y[k] generated by the filtering unit, and the two digital alternating signal data x′[k], y′[k] generated by the differential computing unit; x[k]=A 1 sin ω k (1) y[k]=A 2 sin(ω k −φ) (2) x ′ ⁡ [ k ] = 1 2 ⁢ sin ⁢ ⁢ ω ⁢ { x ⁡ [ k + 1 ] - x ⁡ [ k - 1 ] } ( 3 ) y ′ ⁡ [ k ] = 1 2 ⁢ sin ⁢ ⁢ ω ⁢ { y ⁡ [ k + 1 ] - y ⁡ [ k - 1 ] } ( 4 ) cos ⁢ ⁢ ϕ = 1 A 1 ⁢ A 2 ⁢ { x ⁡ [ k ] ⁢ y ⁡ [ k ] + x ′ ⁡ [ k ] ⁢ y ′ ⁡ [ k ] } ( 5 ) sin ⁢ ⁢ ϕ = 1 A 1 ⁢ A 2 ⁢ { x ⁡ [ k ] ⁢ y ′ ⁡ [ k ] + x ′ ⁡ [ k ] ⁢ y ⁡ [ k ] } ( 6 ) where A 1 and A 2 are the amplitude of each of two alternating signals, ω is the angular frequency, k is one position on the time axis of the sampled data, k+1 is the position one step backward from the position k on the time axis, and k−1 is the position one step forward from the position k on the time axis.