A tunable power amplifier employing digitally controlled accumulation-mode varactor array for 2.4-GHz short-range wireless communication

Abstract

The most popular tunable capacitor topologies in CMOS are the analog varactor and digitally controlled switched capacitor array (SCA). The conventional analog varactor shows a high quality factor (g-factor) in both the minimum capacitance (Cmin) and the maximum capacitance (Cmax) states with a wide tuning range, but it has a poor linearity performance due to the voltage dependent nonlinear capacitance. In case of the digitally controlled switched capacitor array, while it shows a very good linearity, its g-factor in Cmin state is strongly dependent on the substrate loss by the parasitic junction capacitances between p-well, deep n-well, and p-substrate and the substrate resistance. To overcome the aforementioned drawbacks of the analog varactor and the switched capacitor array, the digitally controlled binary-weighted accumulation-mode varactor array (AVA) is proposed. In the simulation, at 2.4 GHz frequency band, the proposed tunable capacitor shows a g-factor of greater than 60 over all states and a tuning range of 3. The inverter-based push-pull power amplifier (PA) with the tunable matching network (TMN) employing the proposed tunable capacitor extends the impedance coverage maintaining the output power of greater than 0 dBm under the worst case for antenna impedance mismatch.