Peak reduction technique for sigma delta modulator in the envelope path of polar transmitter

A major disadvantage of orthogonal frequency division multiplexing (OFDM) is the presence of high peaks in the transmit signal. These can severely impact amplifier efficiency. Envelope Elimination and Restoration (EER) is an architecture designed for improving efficiency by dynamically adjusting the supply voltage to restore the amplitude on a phase modulated input signal. Although this significantly improves overall efficiency there remains the presence of high peaks in the envelope path, these impact the performance of a sigma delta modulator used in the D/A conversion process as well as overall efficiency. In this paper we describe a PAPR reduction technique which can be employed in order to make the input signal more suited for use with a sigma delta modulator. This causes a reduction in in-band and out-of-band distortion as well as overall efficiency improvement.