Orthogonal Frequency Division Multiplexing (OFDM) suffers from a high Peak-to-Average Power Ratio (PAPR). Designing a High Power Amplifier (HPA) with high PAPR is not a wise technique as it roots the amplifier to operate in a non-linear region which is intricate. Linearity and power efficiency are important constraints of HPA which cannot be achieved at the same time. Therefore, perfect linearity is observed when efficiency is low or vice versa and efficiency can be improved by decreasing the PAPR. In this paper, the PAPR is mitigated by using Partial Transmit Sequence (PTS), Selected Mapping (SLM), Hybrid and proposed methods. Analysis of OFDM with high PAPR passing through different HPA models is evaluated in terms of Power Spectral Density (PSD), gain and efficiency for all PAPR reduction methods considered in this work. The results are encouraging by using hybrid PAPR reduction method, HPAs can be operated in a linear region to provide higher efficiency compared to non-hybrid PAPR reduction methods. Hence, hybrid PAPR reduction methods can be used even in future wireless communications systems including 5G and beyond. INDEX TERMS Companding, high power amplifier models, orthogonal frequency division multiplexing, peak to average power ratio, partial transmit sequence, selected mapping.
As Analog CMOS ICs are prone to process variations, a minute change in the W/L ratio during fabrication might vary the specifications of the Op-Amp drastically. It is therefore essential to develop a means by which, the specification of IC can be restored even after fabrication. One such approach is to make Analog ICs programmable, so that the specifications can be restored by applying digital input. But this technique is not direct. It is investigated in our work that this technique drifts the output DC voltage (bias voltage), as the bias current varies and therefore creating threat to linear operation of Op-Amp. In this work, a modified programmable Op-Amp with counter programmable level shifter as third stage is proposed. This circuit reduces the variation of the DC voltage with programming current and allows programming of parameters without affecting the biasing. Our simulations indicate that the modified programmable miller two stage op-amp results in linear variation of Slew Rate with digital input. Programming folded cascode Op-Amp, on the other hand shows considerable variation in gain and phase margin. It is experimentally found that the proposed circuit reduces the effect of DC variation by 70% of the previous work.
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