Class-D amplifiers have gained significant importance in automotive applications due to its high efficiency. However, to meet strict electromagnetic interference (EMI) requirements, an LC filter is necessary, which, unfortunately, introduces nonlinearity to the system. This project proposes an architecture by implementing a dual voltage/current feedback loop to suppress the nonlinearity of the LC filter. The voltage feedback is put after the LC filter to suppress its nonlinearity. The current feedback splits the complex poles from the LC filter to stabilize the system.
By implementing current feedback as the inner loop, this design achieves a significant reduction in the LC filter’s bulk and cost in comparison to state-of-the-art, while maintaining a good total harmonic distortion (THD) level of around -110 dB. This architecture is also robust to +/-30% variations in LC filter cut-off frequency. The chip is fabricated using a 180-nm BCD process, with a die size of 3 mm × 2.28 mm.