Miniature CMOS Stacked Spiral-Coupled Directional Coupler With $-$67-dB Isolation and $-$ 0.8-dB Insertion Loss

摘要

This letter proposes a miniature CMOS stacked spiral-coupled (SSC) directional coupler for a fully integrated CMOS transceiver to isolate the large transmit power from the transmitter to the receiver. It consists of two 90 $^{circ}$-rotated center-aligned SSC coils. The path center of one coil is aligned to the gap center of the other coil. The grounded secondary coil plays a role of ground shielding for reducing the insertion loss. Two capacitors are utilized for tuning the center frequency and isolation level. Fabricated in a standard CMOS process, it achieves an isolation of $-$ 67 dB, an insertion loss of $-$0.8 dB, and a coupling of $-$16.1 dB and only occupies $hbox{0.3} times hbox{0.3} hbox{mm}^{2}$ of silicon area. To the authors' knowledge, this is the first CMOS directional coupler at the UHF band, with the smallest form factor when compared with other implementations of directional couplers.