An adaptive impedance tuning CMOS circuit for ISM 2.4-GHz band

The difficulties encountered in matching an antenna to its optimal impedance are reduced with an adaptive 0.35-mu m CMOS circuit based on several switched shunt capacitors arranged in capacitor banks and on a few external series inductors. As high-quality inductors are difficult to obtain in CMOS, the inductors are placed either in an low-temperature cofired ceramic (LTCC) substrate or is a lumped component outside the core circuit. The circuits, presented here through a range of simulations, are optimized to function within the ISM 2.4-GHz band, but the general approach employed to improve matching can be used for other frequency bands as well. The circuits discussed provide a VSWR <= 2 match for every impedance with VSWR <= 5. There is a 1-dB power loss for a perfect 50 Omega -> 50 Omega transformation, a break-even point at VSWR = 1.5, and a 3-dB increase in delivered power for VSWR = 4.3.