A 0.02% THD and 80 dB PSRR filterless class D amplifier with direct lithium battery hookup in mobile application

This paper presents a fully integrated CMOS filterless class D amplifier that can directly hook up lithium battery in mobile application The proposed amplifier embodies a 2-order feedback path architecture instead of direct feedback of output to input of the integrator to decrease the high frequency intermodulation distortion associated with direct feedback and eliminate the integrator input common mode disturbance from the output in ternary modulation. The prototype class D amplifier realized in 0.35 μm digital technology achieves a THD＋N of 0.02% when delivering 400 m W to an 8 Ω load from V_（DD） =3.6 V. The PSRR of the prototype class D amplifier is 80 dB at217 Hz. Furthermore a filterless method that can eliminate the external LC filter is employed which offers great advantages of saving PCB space and lowering system cost. In addition the prototype class D amplifier can operate in large voltage range with V_（DD）range from 2.5 to 4.2V in mobile application. The total area of the amplifier is 1.7mm~2.