A High-Linearity and Low-EMI Multilevel Class-D Amplifier

This article presents a Class-D audio amplifier for automotive applications. Low electromagnetic interference (EMI) and, hence, smaller <italic>LC</italic> filter size are obtained by employing a fully differential multilevel output stage switching at 4.2 MHz. A modulation scheme with minimal switching activity at zero input reduces idle power, which is further assisted by a gate-charge reuse scheme. It also achieves high linearity due to the high loop gain realized by a third-order feedback loop with a bandwidth of 800 kHz. The prototype, fabricated in a 180-nm high-voltage BCD process, achieves a minimum THD+N of −107.8 dB/−102 dB and a peak efficiency of 91%/87% with 8- and 4-<inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> loads, respectively, while drawing 7-mA quiescent current from a 14.4-V supply. The prototype meets the CISPR 25 Class 5 EMI standard with a 5.7-dB margin using an <italic>LC</italic> filter with a cutoff frequency of 580 kHz.

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