| Oscillators occupy a significant role in all communication systems and most electronic instruments. Among the characteristics of a voltage-controlled oscillator (VCO), phase noise is of paramount importance for the performance of a communication link in which the VCO operates. Driven by the exploding growth of the wireless and telecommunication markets, there appear tremendous interest and tough challenges in the development of low phase noise, low power, and cost effective VCOs for transceiver front-ends. An effort devoted to research and development of a series of base-tuned VCOs in monolithic microwave integrated circuit (MMIC) environment has been carried out, leading to the design and implementation of several distinct circuit configurations optimized for various system applications. A common feature of these units is the direct tuning of the base voltage (or gate voltage) of the core device for frequency control. The absence of varactor not only simplifies the circuit and the fabrication process, but also enhances the noise performance of the resulting VCO. Circuits implemented include a 19-GHz base-tuned GaAs heterojunction bipolar transistor (HBT) VCO, an extremely low phase noise dielectric resonator VCO, a state of the art Q-band AlGaN/GaN High Electronic Mobility Transistor (HEMT) VCO, a W-band direct oscillation VCO, and a highly efficient quad-push harmonic VCO. These chips validated the merits and generality of the base-tuned MMIC VCO approach for different circuit topologies. In addition, emerging technology based on novel high-Q resonators, wafer level packaging and multi-layered MMIC has been explored. Results indicated that base-tuned VCOs offer an attractive solution for signal sources in a variety of MMIC-based subsystems. |
