Towards Ultra Wide Tuning Range and Low Phase Noise mm-Wave VCOs: A Negative Capacitance and BiCMOS Perspective
The ever-increasing demand for data rates/range in modern communication/radar systems coupled with the push towards mm-wave links, has dictated the need for wide tuning range voltage controlled oscillators (VCOs). Nowadays, mm-wave circuits have proliferated into many commercialized applications, including next generation WiFi, auto short range radar (SRR), satellite data and video and mm-wave cellular (LMDS). Traditionally, mm-wave VCOs have been implemented in III-V technologies benefiting from fast device speed and low parasitic capacitance. Therefore, VCOs can operate at mm-wave with reasonable tuning range. However, they suffer from the main drawback of high manufacturing cost and limited level of integration. With lower cost, high transistor fT, ease of integration and power-savings, silicon-based VCOs are very attractive for large-volume applications. Unfortunately, the benefits in digital CMOS technology are not perpetuated easily in designing mm-wave VCOs. The RF components, including inductors and capacitors, suffer from low Q-factor. Therefore, large transconductance (gm) transistors are required to compensate for high losses, leading to pronounced capacitive loading effects that sharply reduce the VCO tuning range. Moreover, transistors with large gm generate high switching noise in mm-wave, which significantly degrade the phase noise of the VCO. In light of these challenges, this talk will present our current research work to build robust Si-based RF circuits with focus on ultra wide tuning-range and low phase noise VCOs.