A low THD clock-free Class-D audio amplifier with an increased damping resistor and cross offset cancellation technique

An increased damping resistor (IDR) replaces high-order loop filter to simply reduce the total harmonic distortion (THD) of Class-D audio amplifier. Besides, cross offset cancellation (COC) technique minimizes the system offset voltage to avoid dc current flows to the speaker in the bridge tied load (BTL) structure. Furthermore, variable switching frequency characteristic in self-oscillating modulation spreads the electro-magnetic interference (EMI) impact out on the output frequency spectrum. Experimental results demonstrate that the proposed Class-D amplifier can deliver 0.55W to the 8Ω load with a 3.3V supply voltage with 150-nm CMOS process. The power efficiency is over 90% and the output THD is smaller than 0.01% (80dB).