Patent ID: 7230485

Claim:
A three state class D amplifier ( 100 ) comprising a first signal path ( 1 ) and a second signal path ( 1 ′) substantially identical with the first signal path ( 1 ), each of the signal paths ( 1 , 1 ′) comprising respective first and second low-pass filter means ( 10 , 10 ′) coupled to respective input signals (Vn, Vp) provided by input means (Inp, In, Ip), first and second ends (A, B) of a load ( 5 ) and to an pulse generator ( 2 ) providing a signal having a frequency substantially higher than a frequency of the input signals (Vn, Vp) for generating respective first and second low-pass filtered signals (SUP, SDW), said low-pass filtered signals (SUP, SDW) being inputted to respective comparing means ( 3 , 3 ′), and the comparing means ( 3 , 3 ′) being coupled to a threshold generator ( 4 ) coupled to the input means (Inp, In, Ip) and to first and second reference signals (Vmax, Vmin) representing an estimation of a maximum and a minimum signal value through the load ( 5 ) and generating an alternating threshold signal (THRES) that is inverse proportional to a difference between the first and second input signals (Vn, Vp) for maintaining a relative high gain of the amplifier in an idle state.