A low-power class-AB amplifier for high-fidelity headphones is presented. The linearity of a class-AB amplifier strongly depends on the loop gain over the audio band and voltage swing. In this paper, a cascode-driven mesh technique limits the number of high-swing nodes in the output stage, thereby preserving the loop gain of the preceding gain stages. A frequency compensation scheme is proposed that extends the unity-gain bandwidth (UGB) and increases the loop gain at 20 kHz. Combining these two techniques, the amplifier achieves -101.4-dB total harmonic distortion plus noise (THD+N) over the full audio band, the lowest ever reported nonlinearity among sub-milliwatt CMOS class-AB amplifiers. The amplifier delivers 51.2-mW peak power to a 16Ω 0.33 -nF load while consuming 0.97 mW of total static power. It has UGB of 12.3 MHz and SNR of 108 dB. These results are consistent when measured over eight test chips. Compared to the recent prior art, the amplifier exhibits >12 dB better linearity and >14-dB dynamic range. This results in 2.5 × improvement in figure of merit (FOM = Peak Load Power/(Quiescent Power × THD+N[%])). It occupies 0.16 mm 2 in a standard 65-nm CMOS.

Original languageEnglish
Article number8600336
Pages (from-to)948-958
Number of pages11
JournalIEEE Journal of Solid-State Circuits
Issue number4
Publication statusPublished - 2019

    Research areas

  • Audio amplifier, cascode-driven mesh bias, class-AB, frequency compensation, headphone driver, high-fidelity (hi-fi), high-linearity, low-power, standard digital CMOS

ID: 53336279