On-Chip T/R Switchable Balun for 5- to 6-GHz WLAN Applications

This brief presents a transmit/receive (T/R) switch combined with a transformer balun. The differential inductor of the transformer balun is symmetrically wound to have the center taps at the outmost winding. The center taps are controlled by nMOS transistors to switch between transmit and receive modes. The transformer balun is matched at 5-6 GHz using parasitic capacitances of the transistors at the differential port and an integrated capacitor at the single-ended port. For high transmit power handling, two transistors are stacked at the transmit path, and the source and drain of the transistors are biased with a dc voltage. The measured insertion loss of the T/R switchable balun is 2.4-3.3 dB at 5-6 GHz with a return loss of less than -16 dB. The amplitude and phase imbalance of the balun, respectively, are less than 1 dB and 4°. The input 1-dB power compression points for the transmit and receive mode are 28 and 20 dBm, respectively. The integrated T/R switchable balun occupies only 0.12 mm2.