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 degrees 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 degrees +/- 5 degrees, 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 mu m 250 mu m.