A modified cross-coupled oscillator
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TECHNICAL PAPER
A modified cross-coupled oscillator Mohammad Bagheri1 • Xun Li1 Received: 27 July 2020 / Accepted: 10 October 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper offers a modified cross-coupled oscillator in 0.18 lm CMOS process. The argument in this paper is to provide an innovative approach to improve the phase noise. The proposed method offers an improved phase noise specification compared to the most traditional ideas in which the higher current dissipations is the key element of the phase noise improvement. The proposed oscillator is capable of an extra oscillation amplitude without increasing the current level, taking advantages of tail current elimination and topology optimization. Analysis of the peak voltage amplitude can verify the optimum performance of the proposed oscillator. This paper also presents a rigorous theoretical phase noise analysis of the proposed oscillator. A closed-form formula is derived of the phase noise in the 1/f 2 region. To verify the derived results, the results are validated against the simulations and illustrate good matches. The overall phase noise error has less than 3 dB error over the offset frequencies from the carrier. Post-layout simulation results at 2.4 GHz with an offset frequency of 1 MHz and 3 MHz show the phase noise of - 127.2 dBc/Hz and - 138 dBc/Hz, respectively, with the current of 1.2 mA in 1.8V supply. In addition, Monte Carlo simulation is used to ensure that the sensitivity of the proposed oscillator to process and frequency variations is very promising.
1 Introduction In the last few decades, many studies have been undertaken to model comprehensively the nature of phase noise in electrical LC oscillators since the oscillators are nonlinear and produce large signals; moreover, the conversion of noise into the phase noise is not constant but varies with time over one oscillation period. Many of the phased-noise formula are more complicated than Leeson’s experimental formulation (Leeson 1966). Commonly, two models are employed widely in the last two decades. The first model provided by Demir et al. (2000), which is rooted in Kartner (1989), is very precise and able to apply to any oscillator such as optic oscillators. In this model the perturbation is decomposed into a phase-deviation component and an additive component termed orbital deviation by Demir et al. (2000). Although this model is extremely accurate and used in modern commercially
& Mohammad Bagheri [email protected] Xun Li [email protected] 1
Department of Electrical Engineering, McMaster University, Hamilton, ON, Canada
available circuit simulators such as Spectrum RF (Pepe and Andreani 2016), the mathematical model is very complicated and does not allow the designer to obtain physical insight into the phase noise generation mechanism. The second model, introduced by Hajimiri and Lee (1998), is a linear time-variant (LTV) model applied only on electrical oscillators. It uses a time-dependent tr
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