New capacitive coupled superharmonic quadrature LC-VCO

Abstract

Abstract:A study of some reported LC quadrature voltagecontrolled oscillators (LC-QVCO) is performed in which it is shown that robustness of the quadrature oscillation varies depending on the coupling configuration. Next, a new superharmonic LC-QVCO is proposed in which the common source node in either of two identical crossconnected LC-VCOs is coupled via a capacitor to the node common between the two varactors in the LC tank of the other LC-VCO. In the proposed coupling configuration there exists a closed loop through which the second harmonic signals circulate. A qualitative argument is presented to justify the robustness of the quadrature nature of the proposed QVCO by applying the Barkhausen phase criterion to the second harmonic signals in the loop. Since the coupling devices are only two capacitors, no extra noise sources and power consumption are added to the core VCOs. A Monte Carlo simulation showed that the phase error of the proposed QVCO is no more than 1 o . Also, generalizing this method to several numbers of VCOs in a loop, multiphase signals can be generated. The proposed circuits were designed using a 0.18-μm RF CMOS technology and simulation results are presented.

A CMOS high-performance inductorless ring VCO with extended monotonic tuning voltage range

“…Multiphase clocks are widely required for wireline and wireless communication systems, e.g., sub-rate clock and data recovery (CDR) circuits [1] and phased-array transceivers [2]. There exist several kinds of reported oscillators which are able to directly generate multiphase clocks, such as rotary travelling-wave oscillators [3], cross-coupled LC oscillators [4], LC-tuned ring oscillators [2] and inductorless ring oscillators [5]. Among them, inductorless ring oscillators are attractive because of the compact layout and no need for complicated inductor modeling.…”