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A digital power amplifier (DPA) that uses switched-capacitor circuits in 90 nm CMOS to efficiently amplify signals with large peak-toaverage power ratios is described in this article. In traditional DPAs, a digital code word representing a desired output envelope voltage is used to control a combination of wide-dynamic range current sources. In contrast, the switched-capacitor power amplifier (SCPA) provides a linear output characteristic by using the digital code word to selectively switch or not switch a bank of integrated capacitors at the RF carrier frequency. Therefore, the SCPA combines the functionalities of an envelope DAC and a power amplifier, and achieves excellent efficiency and output power levels. The SCPA benefits from CMOS transistor scaling, which makes RF SOC integration realizable.
Date of Publication: April 2012