University of Twente Student Theses


Charge steered RF PA

Olieman, Erik (2010) Charge steered RF PA.

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Abstract:This master thesis describes the development of a new type RF PA and upconverter combination. Instead of the normally used voltage steering the amplifier uses charge steering. The parasitic capacitances of the MOSFET in combination with using charge steering form a feedback network that linearizes the amplifier. The developed device is a switching amplifier. For good behavior it uses a capacitor to be able to quickly inject high amounts of current. Derived equations show that feedback becomes better if the gate-drain capacitance is relative large compared to the gate-source capacitance. For this reason a capacitor is periodically placed between the gate and the drain terminals of the amplifying transistor using switches. Half of the time this capacitor is placed there, during this time the charge present on the capacitor determines the output voltage. The other half of the time the amplifying transistor is turned off. The designed RF power amplifier and upconverter combination is designed in 65nm CMOS and operates at a center frequency of 1GHz. The maximum output power is 17.5dBm, its 1dB compression point is only 0.6dB below its maximum output. Up to this output power also two-tone tests perform well, the worst in-band IMD3 component is at -29dBc at an amplitude equal to the 1dB compression point. An efficiency of 21% is reached at the 1dB compression point. Charge injection by the switches decreases performance for lower output values, the range of powers across which the amplifier performs well is around 20dB. The maximum is the 1dB compression point, so the minimum power, where charge injection becomes a significant problem, is 20dB below the 1dB compression point. Another problem is the required capacitances; the total size of the capacitors used in the circuit is over 80pF, which would cost a lot of chip area
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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