Area II: RFIC Design

Our on-going research on RF IC is to develop understanding and circuit techniques for RF ICs that are used in communications applications. Our current major focus is on RF CMOS circuit technology. We are conducting research to stretch the performance RF CMOS circuits to their limit and to demonstrate RF CMOS circuits in building blocks that have not been possibly implemented in CMOS technology. We have successfully designed and demonstrated several RF/microwave circuits with first-pass design success. We have demonstrated a novel multi-band RF (2.4 GHz, 3.5 GHz and 5.8 GHz) phase shifter circuit in 0.18um RF CMOS [J14, C11, and C14] (Figure 1). The phase shifter has an integrated traveling amplifier to compensate multi-band loss and can be used in both receivers and transmitters [J12]. Following this, we demonstrated two RF CMOS amplifiers. The first amplifier is designed and fabricated in 180 nm RF CMOS technology and achieves a measured transducer gain of 10.46 dB with corner frequencies at 3 GHz and 12.6 GHz [C8] (Figure 2). The amplifier has a measured P1dB of 5.6 dBm from 3 GHz to 10 GHz and the third-order intercept point of more than 16.6 dBm. The group delay dispersion is near zero within the passband. To the best of our knowledge, the amplifier masks exactly over the desired UWB bandwidth and has the highest P1dB [C8]. The second amplifier is a novel traveling amplifier that is designed with transistor-level linearization techniques (Figure 3). For the first time, we combine both the multi-gated transistors and capacitance compensation linearization schemes to design the traveling wave amplifier. Using this transistor-level linearization technique, we have achieved an improvement of 5dB in P1dB, 11dBc third-order intermodulation product suppression as compared to a conventional circuit and a highest efficiency of 25% [C7 and J3].

Furthermore, we have developed understanding of RF power amplifiers under antenna mismatches for different types of transistors. Antenna mismatches significantly reduce the performance of a power amplifier and cause large voltage swing that imposes great challenges for low breakdown voltage Si-based devices used in power amplifiers. We have characterized RF SiGe power amplifiers under antenna mismatches. We discovered that at the worst mismatch VSWR 10:1, we can preserve the power amplifier performance by just tuning the phase of the output matching network [J8 and C15] (Figure 4). Along with this research, we have designed and prototyped high power linear phase shifters and circuits to demonstrate the phase tuning concept for power amplifiers under mismatches. We have demonstrated a phase shifter that achieves a measured 180o phase tuning range and P1dB ~ 28 dBm at all tuning voltage [J13]. We are currently preparing the manuscript of the complete tunable circuits in a power amplifier for antenna mismatches [D4]. Currently, we are also investigating the use of RF MEMS in tunable circuits for adaptive power amplifiers.