A new design based on the flipped-structure for RF active inductors is presented. The conventional flipped-active inductor (FAI) composed of only two transistors is considered as a starting structure. However, it suffers from low-voltage swing, which increases the nonlinearity. Additionally, it requires high power consumption to achieve adequate inductance and quality factor values. A circuit topology named cascoded FAI (CASFAI) based on the basic FAI is proposed. A common-gate transistor added in the feedback path of the proposed CASFAI results in an increase of the voltage swing and linearity as well as the feedback gain. The performance metrics of such active inductors are benchmarked by analytical models and validated in the ADS using a 0.18 µm CMOS process. The results indicate that the CASFAI can achieve a notably higher quality factor and higher inductance values while consuming less power in comparison to the basic FAI.Postprint (published version
a b s t r a c tThis paper presents the use of a new structure of active inductor named cascoded flipped-active inductor (CASFAI) in a T-type high-pass tunable output matching network of a class-E RF power amplifier (RFPA) to control the output power and enhance the efficiency. The designed CASFAI behaves as an inductor in the frequency range of 0-6.9 GHz, and has reached to a maximum quality factor of 4406, inductance value of 7.56 nH, 3rd order harmonic distortion better than À 30 dB for 0 dBm input power, while consumes only 2 mW power. In order to consider the performance of the proposed active inductor-based tunable output matching network on the output power level and power added efficiency (PAE) of RFPA, the CASFAI is applied as a variable inductor to the output matching network of RFPA. The overall circuit is designed and validated in ADS in a 0.18 mm CMOS process and 1.5 V supply voltage. The results indicate that by increasing the inductance value of the matching network in constant operating frequency, the PAE peak moves from high power to low power levels without any degradation. Therefore, it is possible to maintain the power efficiency at the same maximum level for lower input drive levels.
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