27.1GHz CMOS distributed voltage controlled oscillators with body bias for frequency tuning of 1.28GHz

Abstract

The feasibility of using standard 0.18µm CMOS technology for low cost wideband monolithic microwave integrated circuits (MMICs) at ~27GHz is demonstrated. Three monolithically integrated distributed voltage controlled oscillators (DVCOs) with a novel gain cell comprising of n-FET common source with p-FET currentsource load are designed. Two of the DVCO's have 3 stages of the gain cell while the third has 4 stages. Top Layer metal is used a coplanar waveguide for producing on-chip inductive elements. An important feature of these DVCOs is the use of body bias variation for very large frequency tuning. Simulation results indicate that the 4-stage DVCO achieves a tuning range of 22.43-23.42GHz i.e 990MHz whereas the 3-stage DVCO has a tuning range of 25.82-27.10GHz i.e 1.28GHz, with respectively ~0.5dBm and ~1dBm change in output power over tuning range for DVCOs. The best value of phase noise for 3-stage DVCO is obtained by applying reverse body bias on n-FETs. For a reverse body bias voltage of -1V, the phase noise is -97.39dBc/Hz at 1MHz offset from 26.87GHz.

A comparative study of different gain cells based microwave CMOS distributed oscillators

“…Wide dynamic tuning range is based on body bias of FETs. Body bias variation changes the gate and drain parasitic capacitances, thereby changing the frequency of oscillation . In addition to body bias, the DVCO with CMOS inverter gain cell uses parallel MOS varactors concurrently to further increase the tuning range of the oscillator .…”

“…One of the main problems being addressed is the frequency tuning of oscillators using the change in FBBof n‐ and p‐MOSFETs and reverse body bias of n‐MOSFETs . For low power VCO operation in CMOS, it is desirable to use parasitic capacitances of transistor as much as possible and frequency tuning using body bias variation . This way of frequency tuning using parasitic capacitances of MOSFETs also has the advantage of higher tuning bandwidth .…”

“…Different gain cells have been suggested in literature for DAs and Oscillators (DOs) in different processes. However, there is no proper comparison between DOs using these different gain cells.…”

“…Proper post layout simulations should be used to compare characteristics of gain cells as well as the performance parameters of Distributed Ocillators using these. A number of gain cells have been suggested in literature to achieve different desirable characteristics of DAs or distributed oscillators (DOs). Commonly used gain cell are n‐MOSFET , and n‐MOSFETs cascode .…”

“…We have also proposed n–p MOSFET gain cell earlier in Ref. i.e. n‐MOSFET common source (CS) with p‐MOSFET passive load.…”