DETECTION OF SUBTHRESHOLD OSCILLATIONS IN A SINUSOID-CROSSING SAMPLING

The detection threshold B of a sinusoid-crossing (SC) detector is impr oved using a new dithering technique. In a real SC detector, B is alwa ys greater than zero because the crossings could be located only with finite accuracy. Dithering is employed to determine the frequency f(s) and the amplitude A(s) of the subthreshold oscillation s(t)=A(s) COS( 2 pi f(s)t), where A(s)<B. The data representation of an analog input signal of bandlimit W, consists of locations (t(1),t(2),...t(2M))=(t(i )) where the signal intersects with the reference sinusoid r(t) =A cos (2 pi f(r)t). A crossing exists within each interval a = 1/2f(r) = T/2 M, where T is the sampling period. If W/2 less than or equal to f(r), and the signal amplitude is less than A for all t values within T, the n SC sampling satisfies the Nyquist sampling theorem. The unknown f(s) value is determined from the power spectrum of the crossing locations of [s(t) + n(sigma)(t)], where n(sigma)(t) is the noise of variance s igma(2). The A(s) value is approximated from the signal-to-noise ratio (R) vs sigma plot. The performance of the technique is studied from t he R plots for different A(s), f(s), and T values.