Silicon-based PIN SPST RF switches for improved linearity

Analysis of PIN diode´s geometric effects on the performance of RF switches is presented with measured data. The impact of periphery-to-area ratio (P/A) is investigated in terms of forward bias resistance and linearity. Theoretical analysis shows the smaller periphery-to-area ratio of PIN diode can reduce not only the forward biased resistance, but also the power handling capability. In addition, positive bias to the PIN diode´s cathode terminal can reduce the effects of Psub-Nwell parasitic diodes, leading to enhanced linearity. Fabricated in a standard 0.18-µm SiGe BiCMOS technology, the 50 µm² PIN Single-pole-single-throw (SPST) RF switch MMIC can achieve an insertion loss of less than 0.69 dB from 2 to 18 GHz with the measured P1dB of 16 dBm.