RF pulse width modulator with reduced spectral regrowth

This paper presents the design of a RF pulse width (PW) modulator for switched-mode power amplification of varying envelope signals such as CDMA or OFDM. The low level of spectral regrow in RF PW modulated signal is ensured by RF pulse swallowing prevention. We proposed a manipulation of the baseband signal envelope in order to remove envelope values below a given amplitude threshold. We show that said envelope processing technique results in the simultaneous enhancement of the adjacent channel leakage ratio (ACLR) and achievement of the required error vector magnitude (EVM) performances. Experimental results for the LTE system with RF-PW modulation show that, with the proposed architecture, an additional 5-10 dB ACLR gain (respect to the conventional RF-PW modulator) can be achieved with EVM levels that completely satisfy 3GPP standard requirements.