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- Guansheng Li, Li Liu, Yiwu Tang, Ehsan Afshari
- J. Solid-State Circuits
- 2012

- Guansheng Li, Ehsan Afshari
- J. Solid-State Circuits
- 2010

This paper presents a distributed multi-phase oscillator based on left-handed LC-ring. In contrast to traditional designs that couple multiple LC-tanks through MOSFETs, it uses an LC-ring as a single high-order resonator that generates multiphase resonant signal. By avoiding coupling MOSFETs which deteriorate phase noise significantly, it can… (More)

- Omeed Momeni, Ehsan Afshari
- J. Solid-State Circuits
- 2011

A systematic approach to designing high frequency and high power oscillators using activity condition is introduced. This method finds the best topology to achieve frequencies close to the of the transistors. It also determines the maximum frequency of oscillation for a fixed circuit topology, considering the quality factor of the passive components. Using… (More)

- Guansheng Li, Yahya M. Tousi, Arjang Hassibi, Ehsan Afshari
- IEEE Trans. on Circuits and Systems
- 2009

We will introduce a design of analog-to-digital converters (ADCs) based on digital delay lines. Instead of voltage comparators, they convert the input voltage into a digital code by delay lines and are mainly built on digital blocks. This makes it compatible with process scaling. Two structures are proposed, and tradeoffs in the design are discussed. The… (More)

- Yahya M. Tousi, Omeed Momeni, Ehsan Afshari
- J. Solid-State Circuits
- 2012

We introduce a novel frequency tuning method for high-power terahertz sources in CMOS. In this technique, multiple core oscillators are coupled to generate, combine, and deliver their harmonic power to the output node without using varactors. By exploiting the theory of nonlinear dynamics, we control the coupling between the cores to set their phase shift… (More)

- Yahya M. Tousi, Omeed Momeni, Ehsan Afshari
- ISSCC
- 2012

Sub-mm-Wave and terahertz frequencies have many applications such as medical imaging, spectroscopy and communication systems. CMOS signal generation at this frequency range is a major challenge due to the limited cut-off frequency of transistors and their low breakdown voltage. A recent work has demonstrated generation of high power at a fixed frequency in… (More)

- Ehsan Afshari, Harish S. Bhat, Ali Hajimiri
- IEEE Trans. on Circuits and Systems
- 2008

We describe how a 2-D rectangular lattice of inductors and capacitors can serve as an analog Fourier transform device, generating an approximate discrete Fourier transform (DFT) of an arbitrary input vector of fixed length. The lattice displays diffractive and refractive effects and mimics the combined optical effects of a thin-slit aperture and lens.… (More)

- R. Han, E. Afshari
- IEEE Transactions on Microwave Theory and…
- 2013

To realize a high-efficiency terahertz signal source, a varactor-based frequency-doubler topology is proposed. The structure is based on a compact partially coupled ring that simultaneously achieves isolation, matching, and harmonic filtering for both input and output signals at <i>f</i><sub>0</sub> and 2<i>f</i><sub>0</sub>. The optimum varactor… (More)

- Guansheng Li, Ehsan Afshari
- Proceedings of the IEEE 2012 Custom Integrated…
- 2012

In this paper, we present a low-phase-noise wide-tuning-range quadrature oscillator using an LC-ring resonator. It achieves low phase noise by employing passive coupling between multiple stages and at the same time it covers a wide tuning range by switching between two resonant modes. Furthermore, the problem of oscillation frequency uncertainty which is a… (More)

We study the steady-state behavior of a damped, driven nonlinear LRC oscillator, where the nonlinearity arises due to voltage-dependent capacitance. The driving or input signal is assumed to be a pure tone. Using an iterative, perturbative solution technique combinedwith an energy conservation argument, we show that the oscillator transfers energy from the… (More)