High-Gain and High-Efficiency EER/Polar Transmitters Using Injection-Locked Oscillators

The envelope elimination and restoration (EER) approach developed by Kahn and its modern derivative, a polar transmitter, are well recognized as highly efficient amplification schemes. This paper presents an EER/polar dual-mode transmitter using injection-locked oscillators (ILOs). For an EER operation, an ILO that is combined with a mixer and a low-pass filter in the proposed architecture extracts an envelope signal and a phase-modulated RF signal from an input RF signal with complex modulation. The phase-modulated RF signal is then amplified efficiently by a class-E power amplifier (PA). Additionally, the envelope signal is reconstructed at the PA output by modulating the supply voltage of the PA. For a polar operation, the necessary phase modulation and envelope modulation are generated in the digital domain instead. Moreover, the phase-modulated RF signal is injected into an ILO and the ILO output is amplified by a class-E PA while supply-modulated with the envelope signal. For wideband code-division multiple access (WCDMA) signals, the implemented prototype transmitter achieves a 20.8-dB gain and 44% power-added efficiency (PAE) at an average output power of 25.8 dBm. For enhanced data rates for GSM evolution signals, it delivers 26.6 dB of gain and 48.7% PAE at an average output power of 26.6 dBm. Furthermore, to compensate for the AM-AM and AM-PM distortions of the PA, the linearity is improved using static digital predistortion. Experimental results demonstrate that the proposed EER/polar transmitter using ILOs has a high gain, high efficiency, and good linearity.