RF Transmitter Architectures for Nomadic Multi-radio: A Review of the Evolution Towards Fully Digital Solutions

Envelope Factorization with Partial Elimination and Recombination, EF-PER, a New Linear RF Architecture

“…The higher the PAPR, the higher is the necessary backoff and the lower the power efficiency. Several approaches [1], [2], [3], [4] were investigated to improve the tradeoff between linearity and efficiency by modifying the input signal (crest factor reduction, predistortion), the PA design [1] (Doherty, Switch-mode PA, DPA/RFDAC) or the transmitter architecture and the PA design at the same time (LINC/CALLUM, EER, ET).…”

“…Besides, the architecture using this type of PA has to be modified to take into account the envelope amplitude variation. One approach is to encode the amplitude variation, with Pulse Width Modulation (PWM) or ΣΔ coding [4], [11], in order to suppress the dynamic. In these cases, a filtering of the RF signal is mandatory, at the PA output, to meet the spectrum mask requirements of the standards.…”

“…Digital PA and RF-DAC [4], [9], [12] can be used at low RF power of emission (Bluetooth for example) but they present the same kind of technological limitations and filtering needs as switch-mode PAs.…”

“…EER [1], [2], [4], [16][17][18] relies on a factorization of x(t) into a product of a constant amplitude bandpass signal x' 2 (t) = cos(ωt + φ(t)) and a baseband envelope signal x' 1 (t) = A(t). The constant amplitude bandpass signal x' 2 (t) can be amplified with an RF PA which operates in a high efficiency class.…”

“…The overall efficiency is mainly the product of the two PAs efficiencies. In such recombination, the time mismatch is critical [4], [19], [20]. The bandwidths of the signals x' 2 (t) and x' 1 (t) are wider than that of the original signal x(t), highly challenging the design of the baseband PA. Another difficulty arises when lowest values of the envelope occur on the supply voltage while the PA has a constant input RF power.…”