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The design of a new high-efficiency switching power amplifier with an ultralow-power spread spectrum clock generator (SSCG) is first reported in this paper. An effective low-power frequency modulation method is first proposed to reduce the electromagnetic interference of the pulse width modulation class D power amplifier without degrading its power efficiency. Also, a simple RC voltage feedback circuit is used to reduce the total harmonic distortion (THD). This amplifier proves to be a cost-effective solution for designing high fidelity and high efficiency audio power amplifiers for portable applications. Measurement results show that the power efficiency and THD can reach 90% and 0.05%, respectively. The power dissipation of the SSCG is only 112 ??W. The harmonic peaks of the switching frequency are greatly reduced when the SSCG technique is applied to the amplifier design. The impact of the SSCG on the THD of the class D power amplifier is also first reported in this paper. This switching power amplifier is implemented using a Taiwan Semiconductor Manufacture Company (TSMC) 0.35- ??m CMOS process.