Conditions for positivity of an energy operator

The authors present necessary and sufficient conditions such that the output from the Teager-Kaiser (1989) energy operator /spl lsqb/s/spl dot/(t)=ds(t)/dt/spl rsqb/ /spl Psi//sub c//spl lsqb/s(t)/spl rsqb/=s/spl dot//sup 2/(t)/spl minus/s(t)s/spl uml/(t) for continuous-time signals s(t) and the output from the corresponding discrete-time energy operator /spl Psi//sub d//spl lsqb/s(n)/spl rsqb/=s/sup 2/(n)/spl minus/s(n+1)s(n/spl minus/1) be non-negative everywhere. These operators have been shown to be effective for AM and FM demodulation in several useful classes of signals, such as speech and image signals.>