Tunable Broadband MMIC Active Directional Coupler

This paper presents a tunable broadband monolithic microwave integrated circuit (MMIC) active directional coupler that demonstrates tuned coupling gains (from 3 dB to -6 dB) and tuned center frequencies. The active directional coupler consists of two broadband near 90° phase shifters, two amplifiers between these phase shifters, and varactors at the connection nodes of the phase shifters and the amplifiers. It was designed and fabricated in a 130-nm process. For a 3-dB coupling gain, the 10-dB directivity bandwidth is 2.3 GHz (from 5.5 to 7.8 GHz). The amplitude imbalance is 3 dB ±0.5 dB, the phase imbalance is 180° ± 5°, and the noise figure is less than 8 dB in the range of 4 to 9 GHz. The return losses are better than 19 dB and the insertion loss is less than 1.2 dB in the range of 4 to 9 GHz. The measured IP1 dBs for 3-dB and 0-dB coupling gains at 6.7 GHz are 0.3 dBm and 1.8 dBm, respectively. The supply voltage is 1.2 V. The measured power consumptions at 3-dB, 0-dB, - 3-dB, and - 6-dB coupling gains are 22 mW, 6 mW, 3 mW, and 1 mW, respectively. The core chip area, including two on-chip DC bias inductors, is 470 μm × 250 μm.