Kahn envelope elimination and restoration technique using injection-locked oscillators

The envelope elimination and restoration (EER) technique, which was proposed by Kahn, is a recognized means of highly-efficient linear amplification. This paper presents a novel EER transmitter using injection-locked oscillators (ILOs). In the proposed architecture, an ILO that is combined with a mixer and a low-pass filter extracts an envelope signal and a phase-modulated RF signal from an RF input signal with time-varying envelope modulation. Then, the phase-modulated RF signal is efficiently amplified by a Class-E power amplifier (PA) and the envelope signal is restored at the PA output by modulating the supply voltage of the PA. The constructed prototype of the EER transmitter achieves a 21 dB power gain and a 36% power-added efficiency at an average output power of 23 dBm for Enhanced Data rates for GSM Evolution (EDGE) signals, meeting the spectral mask specifications without using any pre-distortion techniques.