ΣΔ modulator for digital wireless architecture: A review

This paper studies Sigma-Delta (ΣΔ) technique to embed a complex modulation scheme such as orthogonal frequency division multiplexing (OFDM) into a single `on´-`off´ bit stream operating at the carrier frequency. The amplitude of the signal is related to the pulse widths and the phase to the pulse position. This paper concentrates on all digital up-converter structures of ΣΔ modulator architecture. The binary nature of their output removes the need for analog components in the up-conversion chain. Their outputs can be used directly to drive the switch mode power amplifier (SMPA) for high efficiency operation.