A 250 mW class D design with direct battery hookup in a 90 nm process [audio band switching amplifier]

A "battery connect" compatible class D (switching) amplifier which is fully integrated in a 90 nm digital CMOS process is presented. The integration of the amplifier requires no additional masks, processing, or cost. This paper includes a brief description of the circuit techniques that enable direct battery connection and allow support for the 4.6 V_P2P output swing using devices that operate solely with low gate voltages. The achieved SNR over an audio (20 Hz to 20 kHz) bandwidth is 84 dB and the total harmonic distortion (THD) is better than 0.05% at full power. The power supply rejection (PSR), which is a crucial parameter in modules connected directly to the battery, is measured at greater than 58 dB at 217 Hz. The area of the switching amplifier is <0.77 mm², where the power devices occupy approximately half the total.