A lOGHz CMOS Distributed Voltage Controlled Oscillator'

VDD A 10 GHz CMOS distributed voltage controlled oscillator (DVCO) is designed in a 0.35pm BiCMOS process technology using only CMOS transistors. The oscillator achieves a tuning range of 12% (9.3 GHz to 10.5 GHz) and a phase noise of -1 14 dBc/Hz at 1 MHz offset from a carrier frequency of 10.2 GHz. The VCO uses two different simultaneous tuning techniques which allow for a coarse and fine I tuning of frequency in a frequency synthesizer. The oscillator provides an output power of -7 dBm without any buffering, drawing 14mA of dc current from a 2.5V power supply. Introduction Recently, CMOS has emerged as a promising low-cost alternative to compound semiconductor or silicon bipolar technology for integration of microwave front-end circuits. Unlike traditional approaches, CMOS makes it possible to integrate the microwave front-end and digital back-end on the same chip and provides a system-on-a-chip solution at microwave frequencies. Although it is possible to design LC oscillators on a silicon substrate up to 10 GHz, it becomes excessively hard to achieve a wide tuning range and good phase noise as the frequency of operation approaches f, of transistors [ 11. This is mainly due to the trade-off between the self-resonance frequency and the quality factor, Q,of the inductors and varactors. This trade-off becomes prohibitive as the operation frequency increases. This limitation has made it more attractive to pursue altemative approaches, such as distributed oscillators. Distributed amplifiers have been studied for over 50 years [2][3][4]. Skvor, et a1 proposed to build a VCO by operating a distributed amplifier in the reverse gain mode, using the output from the idle drain load as the feedback output [5]. A 4 GHz distributed oscillator was demonstrated using four discrete pHEMTs and microstrip lines on a printed circuit board (PCB) [ 6 ] . In 1999, Kleveland, et al showed an integrated (with off-chip termination and bias) distributed oscillator operating at 17 GHz without any tuning capability using a 0.18 pm CMOS technology [7]. The forward gain mode instead of reverse gain mode was used to demonstrate that CMOS is usable for oscillator applications at microwave frequencies. I Figure 1 . Basic distributed oscillator with isolated drain and gate bias. transistor gain in CMOS technologies. Therefore, a new tuning scheme must be devised. In this paper, we first discuss the basic principle and design issues of DVCOs. Then, the tuning techniques are discussed. Special attention will be paid to the layout and topology considerations. Finally, measurement results are shown.