Analytical and experimental study of tuning range limitation in mm-wave CMOS LC-VCOs
19 May 2013-pp 2468-2471
TL;DR: An analytical model for predicting the tuning range of CMOS mm-wave LC voltage-controlled oscillators (LC-VCOs) is presented and the frequency dependent quality factor of the LC-tank is performed to characterize the tank loss.
Abstract: In this paper, we present an analytical model for predicting the tuning range of CMOS mm-wave LC voltage-controlled oscillators (LC-VCOs). A detailed analysis of the frequency dependent quality factor (Q) of the LC-tank is performed to characterize the tank loss. The frequency dependent Q is used to size the transconductance (gm) of the cross-coupled pair to satisfy the VCO startup condition. The relationship between the cross-coupled pair gm and the operating frequency is also derived. With the above relationships, the frequency dependent tuning range is further calculated and compared with simulation results. To verify the analysis, three CMOS mm-wave VCOs are fabricated in a 130 nm CMOS process. The measured tuning range of the 26 GHz, 34 GHz and 40 GHz VCO is 25%, 21% and 18%, respectively, which is consistent with the presented tuning range model.
Citations
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TL;DR: A detailed analysis of the ultimate performance bound in simultaneously achieving low phase noise and wide tuning range in CMOS VCOs is presented.
Abstract: The unprecedented interest in high bandwidth applications in the mm-wave range has set off a wave of research exploring techniques that enable wide tuning range voltage-controlled oscillators (VCOs). Low frequency CMOS LC-VCOs ( <;10 GHz) have been well studied in the literature and several approaches have been developed to optimize their performance. However, there lie several interesting challenges in the mm-wave space, specifically close to the fT/fmax, that motivate the need for analyzing the tuning range and phase noise in mm-wave VCOs. This paper presents a detailed analysis of the ultimate performance bound in simultaneously achieving low phase noise and wide tuning range in CMOS VCOs. The analysis is conducted on a 130 nm CMOS process, and confirmed by measurement results on three VCOs at 26 GHz, 34 GHz and 40 GHz. Finally, the impact of CMOS technology scaling (from 130 nm down to 45 nm), on the achievable performance bounds is analyzed and presented.
14 citations
TL;DR: The analysis indicates that thick gate cross-coupled pair VCOs achieve better phase noise at the expense of power consumption and maximum tuning range with the technology down scaling.
9 citations
TL;DR: The proposed analysis shows that LC cross-coupled oscillators have an additional and higher pure imaginary natural frequency at which the circuit cannot oscillate and increasing the speed of the oscillator does not satisfy the start-up condition of oscillators.
Abstract: In this brief, a cross-coupled oscillator is analyzed based on the two-port network theory and the $Y$ - parameter model for a transistor. Contrary to the previous works, the proposed analysis shows that LC cross-coupled oscillators have an additional and higher pure imaginary natural frequency at which the circuit cannot oscillate. The analysis investigates the sufficient condition at which the circuit is able to oscillate at this higher frequency. For the oscillation at the higher frequency mode, we propose adding an extra stage and making a three-stage ring oscillator. The equations obtained from this analysis indicate that the oscillation start-up condition depends on the oscillation frequency. Hence, increasing the speed of the oscillator does not satisfy the start-up condition of oscillators. Our analysis shows that the maximum frequency, in which the circuit stops oscillation in the ring oscillator, is higher than the cross-coupled oscillator and this maximum frequency is very close to the maximum frequency of the transistor.
8 citations
04 May 2014
TL;DR: This paper presents the main challenges in the design of wide tuning range LC voltage controlled oscillators (LC-VCOs) in CMOS technologies and design trade-offs such as tank losses, phase noise, and power consumption are discussed and analyzed.
Abstract: This paper presents the main challenges in the design of wide tuning range LC voltage controlled oscillators (LC-VCOs) in CMOS technologies. Design trade-offs such as tank losses, phase noise, and power consumption are discussed and analyzed. A VCO that has a wide tuning range that covers frequencies from 5.5 GHz to 10.2 GHz was designed and fabricated in a 65 nm CMOS process. The worst case measured phase noise is -83 dBc/Hz at 1 MHz frequency offset from the carrier. The design occupies 0.125 mm 2 silicon area, and dissipates 11 mW (excluding the buffers).
1 citations
Cites background from "Analytical and experimental study o..."
...The quality factor QL of an inductor L can be expressed as [7]:...
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01 Jan 2013
TL;DR: In this article, an inductance redistribution technique to equally space sub-band coarse tuning characteristics is proposed and implemented to overcome the limitations of high frequency LC-voltage controlled oscillator (LC-VCO).
Abstract: The growing demand for higher data rate in wireless transceivers continues to consume available bandwidth and move towards multi-band/multi-channel mm-wave systems to satisfy latest specifications and be compatible with legacy standards. One of the critical components, the LC-voltage controlled oscillator (LC-VCO), is required to have low phase noise while maintaining wide tuning range to achieve low bit error rates (BERs). Due to the large parasitic capacitance and high losses in silicon based technologies, extending the tuning range and reducing phase noise is becoming very challenging. This dissertation studies and proposes novel architectures and circuit techniques to overcome the limitations of high frequency LC-VCOs. Different LC-VCO architectures are reviewed and the performance is summarized and compared. The components in LC-VCOs are theoretically analyzed and a prototype VCO is designed. An inductance redistribution technique to equally space sub-band coarse tuning characteristics is proposed and implemented. To predict the tuning range, a detailed analysis of the frequency dependent quality factor (Q) of the LC-tank is performed to characterize the tank loss. The frequency dependent Q is used to size the transconductance (gm) of the cross-coupled pair to satisfy the VCO startup condition. The relationship between the cross-coupled pair gm and the operating frequency is further derived.
1 citations
References
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TL;DR: In this paper, a charge-based model of the intrinsic part of the MOS transistor is presented, which is based on the forward and reverse charges q/sub f/ defined as the mobile charge densities, evaluated at the source and at the drain.
Abstract: This paper presents an overview of MOS transistor modeling for RF integrated circuit design. It starts with the description of a physical equivalent circuit that can easily be implemented as a SPICE subcircuit. The MOS transistor is divided into an intrinsic part, representing mainly the active part of the device, and an extrinsic part responsible for most of the parasitic elements. A complete charge-based model of the intrinsic part is presented. The main advantage of this new charge-based model is to provide a simple and coherent description of the DC, AC, nonquasi-static (NQS), and noise behavior of the intrinsic MOS that is valid in all regions of operation. It is based on the forward and reverse charges q/sub f/ and q/sub r/ defined as the mobile charge densities, evaluated at the source and at the drain. This intrinsic model also includes a new simplified NQS model that uses a bias and frequency normalization allowing one to describe the high-order frequency behavior with only two simple functions. The extrinsic model includes all the terminal access series resistances, and particularly the gate resistance, the overlap, and junction capacitances as well as a substrate network. The latter is required to account for the signal coupling occurring at RF from the drain to the source and the bulk, through the junction capacitances. The noise model is then presented, including the effect of the substrate resistances on the RF noise parameters. All the aspects of the model are validated for a 0.25-/spl mu/m CMOS process.
194 citations
"Analytical and experimental study o..." refers methods in this paper
...To obtain Cvar and Q, the varactor model in [6] is adopted....
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TL;DR: A low-phase-noise wide-tuning-range oscillator suitable for scaled CMOS processes that switches between the two resonant modes of a high-order LC resonator that consists of two identical LC tanks coupled by capacitor and transformer.
Abstract: In this paper we will present a low-phase-noise wide-tuning-range oscillator suitable for scaled CMOS processes. It switches between the two resonant modes of a high-order LC resonator that consists of two identical LC tanks coupled by capacitor and transformer. The mode switching method does not add lossy switches to the resonator and thus doubles frequency tuning range without degrading phase noise performance. Moreover, the coupled resonator leads to 3 dB lower phase noise than a single LC tank, which provides a way of achieving low phase noise in scaled CMOS process. Finally, the novel way of using inductive and capacitive coupling jointly decouples frequency separation and tank impedances of the two resonant modes, and makes it possible to achieve balanced performance. The proposed structure is verified by a prototype in a low power 65 nm CMOS process, which covers all cellular bands with a continuous tuning range of 2.5-5.6 GHz and meets all stringent phase noise specifications of cellular standards. It uses a 0.6 V power supply and achieves excellent phase noise figure-of-merit (FoM) of 192.5 dB at 3.7 GHz and >; 188 dB across the entire tuning range. This demonstrates the possibility of achieving low phase noise and wide tuning range at the same time in scaled CMOS processes.
165 citations
"Analytical and experimental study o..." refers background in this paper
...In low frequency LC-VCOs, wide tuning range and low phase noise can be obtained by employing a parallel combination of coarse-tuned switched capacitors and a fine-tuned MOS varactor [1]....
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TL;DR: This work demonstrates the widest tuning range in percentage among the CMOS VCOs at millimeter-wave frequencies and uses a 0.18-mum CMOS process to design and implement a 40-GHz VCO.
Abstract: The design of a wide-tuning-range millimeter-wave CMOS VCO is presented in this paper. In contrast to the conventional wideband topologies, a nonuniform standing-wave oscillator utilizing tapered gain elements, switched transmission lines and distributed varactors is employed to provide an extended output range with the coarse and fine frequency tuning. Due to the use of the transmission line architecture and the position-dependent amplitude of the standing waves, the loading effects of the varactors and the MOS switches can be alleviated, enabling the VCO to operate at higher frequencies. Using a 0.18-mum CMOS process, a 40-GHz VCO is designed and implemented. Consuming a DC power of 27 mW from a 1.5-V supply voltage, the fabricated circuit exhibits a frequency tuning range of 7.5 GHz with an output power level ranging from -13.6 to -4 dBm. The measured phase noise at 1-MHz offset is lower than -96 dBc/Hz within the entire frequency range. This work demonstrates the widest tuning range in percentage among the CMOS VCOs at millimeter-wave frequencies.
115 citations
"Analytical and experimental study o..." refers background in this paper
...To counter these issues, the use of distributed transmission line structures [2] has been proposed and demonstrated a wide tuning range at the expense of increased power consumption and chip area....
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TL;DR: A nonlinear perturbation model of a complementary LC-tuned voltage-controlled oscillator is derived, obtaining closed-form expressions for both the amplitude and the harmonics of oscillation, as well as for the correction of the oscillation frequency due to the nonlinear effect of varactors.
Abstract: A nonlinear perturbation model of a complementary LC-tuned voltage-controlled oscillator is derived, which consists of two mutually-coupled second-order differential equations. The first-order approximate periodic solution of the describing equations is found, obtaining closed-form expressions for both the amplitude and the harmonics of oscillation, as well as for the correction of the oscillation frequency due to the nonlinear effect of varactors. This allows us to find the tuning curve in explicit form. The accuracy of presented formulas was validated by circuit simulations.
31 citations
"Analytical and experimental study o..." refers background in this paper
...Excluding other exotic structures such as push-push VCOs and magnetically tuned/coupled VCOs, the VCO tuning range is seen to drop proportionally to 1/ √ f [4]....
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TL;DR: A nonlinear perturbation model of VCOs is presented, as well as a method for finding their steady-state oscillation, overcoming the limitation of previous analyses which rely on the solution of the tank balance equation only.
Abstract: A method for the nonlinear analysis of voltage-controlled oscillators (VCOs) is presented, accounting for the nonlinear effect of both the varactors and the active devices. A nonlinear perturbation model of VCOs is presented, as well as a method for finding their steady-state oscillation, overcoming the limitation of previous analyses which rely on the solution of the tank balance equation only. Simple formulas for predicting the oscillation and its frequency correction due to the effect of nonlinearities are presented, allowing us to accurately predict the tuning curve of VCOs as well as the amplitude to phase-noise conversion due to the varactors. Their accuracy was validated by circuit simulations.
25 citations
"Analytical and experimental study o..." refers background in this paper
...Harmonic distortion, which is produced by a low tank Q, also increases [7]....
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