Improve PSRR and Output Power Capability by Using a Boosted Class D Amplifier

Dominique Romeo
ON Semiconductor France

In mobile phone applications, Power Supply Rejection Ratio (PSRR) and Output Power capability are key parameters. In that kind of portable application, class D amplifiers (CDA), thanks to a high efficiency and a large output capability, are more and more popular. However, compared to a class AB amplifier, the PSRR is still one of the class D drawbacks. When a state of the art class AB amplifier can achieve a PSRR as high as 100 dB at 217 Hz and fully reject supply noise like GSM burst, classical class D amplifier difficultly go under 80 dB. Moreover, even if the CDA Output Power capability is larger than class AB, this output power is still dependent upon the battery voltage level. This paper depicts the concept of Boosted Class D Amplifiers (BCDA), which could be an alternative to solve these two limitations: PSRR and output power variation.

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