Series Resonance Research Articles

Realization of optically transparent and broadband frequency selective rasorber using thin copper wire

Numerous studies have been made to design broadband frequency selective rasorber (FSR). However, it is still a challenge to realize optically transparent FSR, due to the difficulty in realizing high transparency, high-quality factor(Q) parallel resonance, and low-Q series resonance simultaneously. Here, we propose a new method to design transparent FSR for the first time. To break through the technical barrier, a thin copper wire with a different configuration method is utilized to design lossy layer, which can realize high transparency, in-band transmission, and out-of-band absorption concurrently. The proposed FSR is configured by cascading a transparent lossy layer above a transparent frequency selective layer with an air space to separate them. We adopt the equivalent circuit model, electric field distribution, and loss distribution to reveal the physical mechanism of the FSR. The simulation results show that the transmission loss is 1 dB at 8.3 GHz, and the reflection amplitude is less than −10 dB in 2.7–8.9 GHz. The FSR can achieve 96.3% optical transparency theoretically. A prototype is fabricated and measured to validate the proposed design. The measured results achieve good agreement with the simulated results. The proposed FSR can act as a stealth radome for transparent components of ships and aircrafts. The application scenarios can be extended to communication and imaging systems.

Synchronously controlled optical modes in the transmittance and reflectance spectra of multilayer photonic structure with dual-frequency nematic liquid crystal.

A method for electrically controlled synchronous mode tuning in the transmittance and reflectance spectra of a photonic structure consisting of an asymmetric dielectric Fabry-Pérot microcavity and an ultrathin metallic film has been proposed. The excitation of a broadband Tamm plasmon polariton at a metal/Bragg mirror interface is accompanied by the two phenomena opposing one another. Due to the strong absorption induced by the metal, a sufficient rejection level in the reflection of the off-resonant radiation has been obtained in a wide spectral range, which almost coincides with the photonic band gap, while at the cavity mode frequencies the structure becomes transparent for the reflected radiation. This leads to the appearance of a series of narrow resonance peaks in the reflectance spectra that coincide in frequency with the transmittance peaks. Based on the structural transformations in the dual-frequency nematic liquid crystal used as a photonic structure defect, the tuning of the modes corresponding to the extraordinary waves to both the short- and long-wavelength spectral ranges has been implemented.

Experimental dielectronic recombination rate coefficients for lithium-like 40Ca17+

The rate coefficients for dielectronic recombination (DR) of lithium-like 40Ca17+ ions with ∆n = 0 core excitations are derived from electron–ion recombination spectra measured with merged-beams method at the heavy-ion storage ring CSRm. The experimental DR spectrum, in the electron–ion collision energy range of 0 to 42 eV in the center-of-mass frame, comprises of all DR resonance peaks belong to the 2s 2 S 1/2 → 2p 2 P 1/2, 3/2 core excitations. The resonant energies and strengths for the resolved resonances in 2pjnl series are determined by fitting of the measured DR peaks. The further interpretation of the measured DR rate coefficients has been performed by calculating the DR rate coefficients with relativistic configuration-interaction method implemented in flexible atomic code (FAC) and compared with the experimental results. The experimental results and FAC calculations are found to be in a good agreement within the experimental uncertainties. Moreover, temperature dependent plasma rate coefficients were constructed from 4 × 103 to 1 × 107 K energy region by convoluting experimental and theoretical DR rate coefficients with the Maxwellian energy distribution function and then compared with previously available data. The plasma DR rate coefficient is found to be significantly underestimated by the early theoretical data calculated by Jacobs et al, and Mazotta et al in the low temperature. In contrast, a very good agreement has been found between the theoretical DR data of Gu and Colgan et al and the presently measured results at the low temperature region. Therefore, the results in this work composed of a bench-mark data set for plasma modeling at the photoionized temperature range. We have also provided a fit to our measured and theoretical plasma rate coefficients for low temperature plasma modeling.

CPT resonances under multifrequency pumping

The possibility of detecting coherent population trapping (CPT) resonances with combined microwave and HF modulation of the injection current of a diode laser has been demonstrated for the first time. A series of resonances is observed, separated from each other by half the RF modulation frequency.

Power- and Spatial-Dependent Characterization of Reflection and Transmission Electric Parameters of an Argon Microwave Plasma

In this article, the power- and spatial-dependent macroscopic electrical transmission and reflection properties of an argon microwave plasma are analyzed. A custom two-port coaxial prototype is built with a variable spatial gap between two electrodes. All measurements are based on the extension of the large-signal scattering parameter (Hot-S) measuring environment and are proof-of-concept for the determination of plasma properties without an external probe. The coaxial topology of the prototype has a fixed reference impedance so that the reference planes can be located at the tip of both electrodes. An equivalent lumped element circuit valid over a wide bandwidth is investigated to simulate the linear macroscopic electromagnetic reflection and transmission properties of the plasma. A series-resonance circuit is chosen since its representation is capable of covering the measurements from 10 to 40 W of input power and gaps from 1 to 3 mm. With this circuit, a continuous relationship between the impedance, power, and the spatial dimensions of the plasma is found.

Self-Driven Current-Doubler Synchronous Rectifier and Design Tuning for Maximizing Efficiency in IPT Systems

A novel driving circuit for a current-doubler synchronous rectifier (SR) to inductive power transfer (IPT) applications is proposed in this article using only auxiliary windings in the existent rectifier output filter inductors to drive active switches. The proposed SR overcomes the limitations of the traditional driving schemes because it does not require any processing, analog circuits, gate driver circuits, or current measurement, normally used in the conventional SR applied to IPT systems. The proposed configuration presents a simple and robust operation considering usual parametric variation in IPT systems, such as coupling factor, misalignment, load variation, and component tolerances. Moreover, the same size and weight of the conventional diode rectifier board are maintained due to the simplicity of the self-driven circuit. The proposed configuration allows increasing the global efficiency by reducing the conduction losses of the output rectifier and previous stages. A resonant circuit design procedure using an iterative process to find the maximum efficiency point considering the self-driven SR is proposed to maximize the global system efficiency. A 100-W resonant series–parallel IPT prototype is developed to validate the performance of the proposed self-driven SR circuit presenting a maximum global efficiency equal to 94.8%.

Piezoelectric MEMS Acoustic Transducer with Electrically-Tunable Resonant Frequency.

The paper presents a technique to obtain an electrically-tunable matching between the series and parallel resonant frequencies of a piezoelectric MEMS acoustic transducer to increase the effectiveness of acoustic emission/detection in voltage-mode driving and sensing. The piezoelectric MEMS transducer has been fabricated using the PiezoMUMPs technology, and it operates in a plate flexural mode exploiting a 6 mm × 6 mm doped silicon diaphragm with an aluminum nitride (AlN) piezoelectric layer deposited on top. The piezoelectric layer can be actuated by means of electrodes placed at the edges of the diaphragm above the AlN film. By applying an adjustable bias voltage Vb between two properly-connected electrodes and the doped silicon, the d31 mode in the AlN film has been exploited to electrically induce a planar static compressive or tensile stress in the diaphragm, depending on the sign of Vb, thus shifting its resonant frequency. The working principle has been first validated through an eigenfrequency analysis with an electrically induced prestress by means of 3D finite element modelling in COMSOL Multiphysics®. The first flexural mode of the unstressed diaphragm results at around 5.1 kHz. Then, the piezoelectric MEMS transducer has been experimentally tested in both receiver and transmitter modes. Experimental results have shown that the resonance can be electrically tuned in the range Vb = ±8 V with estimated tuning sensitivities of 8.7 ± 0.5 Hz/V and 7.8 ± 0.9 Hz/V in transmitter and receiver modes, respectively. A matching of the series and parallel resonant frequencies has been experimentally demonstrated in voltage-mode driving and sensing by applying Vb = 0 in transmission and Vb = −1.9 V in receiving, respectively, thereby obtaining the optimal acoustic emission and detection effectiveness at the same operating frequency.

A novel dual mode configurable and tunable high-gain, high-efficient CMOS power amplifier for 5G applications

This paper presents a novel dual mode configurable and tunable power amplifier (PA) that achieves a wide-bandwidth and high gain across a operational frequency spectrum of 20 to 30 GHz. The proposed PA used two-stage tunable PA which can be configured as a tunable synchronous mode or tunable stagger-tuned mode PA. PA is implemented by using a distortion-free varactor at the input and output tank of PA. The designed PA includes a high-Q CMOS active inductor (CAI) which provides a widely tunable output matching network. The resistive feedback is used for self-biasing in the designed PA which helps to enhance the linearity, stability of common source (CS) amplifier. The inter-stage impedance matching network consists of shunt and series resonance circuits are employed for maximum power added efficiency (PAE). Furthermore, the capacitive coupled reuse technique is implemented in each stage between the cascaded transistor to reduce the power consumption. A proposed PA is designed using a 65 nm CMOS technology. A measured power gain at the synchronous operation of PA is 28.4 ±0.5 dB with 1.31 GHz bandwidth while power gain at staggered operation is 22.1 ±0.5 dB with 3.71 GHz bandwidth. The measured saturated power (Psat) is 14.21 dBm and the noise figure (NF) is 5.2 dB. The group delay (GD) variation for staggered operation is 57 ±10 ps from 20-30 GHz. A proposed PA exhibits good linearity (IIP3) of 14.5 dBm and PAE is 47.5 % at 24 GHz. The power consumption of a designed PA is 48.56 mW with a supply voltage of 1.2 V.

Nonlinear transmission line (NTL) model study of electromagnetic effects in high-frequency asymmetrically driven capacitive discharges

In this work, we generalize a nonlinear transmission line (NTL) model introduced in a previous work [Liu et al. Plasma Sources Sci. Technol. 30, 045017 (2021)] to achieve more comprehensive simulations. The improved NTL model allows a variable-sized (instead of a one grid cell) vacuum spacer between the powered and grounded electrodes and takes into account the (previously neglected) electron-neutral elastic collision frequency term in the plasma dielectric constant, and the radial variation of the plasma density. Using this model, we study the effects of the spatial and series resonances, associated with the (axially) z-antisymmetric and z-symmetric radially propagating surface wave modes, and the nonlinear harmonic excitations on the plasma uniformity. We conduct simulations in which we increase the driving frequency f from 30 to 120 MHz for an asymmetric capacitive argon discharge at a fixed pressure and electron power of pg=20 mTorr and Pe=40 W, respectively. The first antisymmetric mode resonance frequency fa1 occurs between 80 and 90 MHz, and the first symmetric mode resonance frequency fs1 occurs at about 100 MHz. The powered electrode sheath becomes smaller than the grounded electrode sheath for f≈fa1, and the source voltage reaches a minimum for f≈fs1. The radially varying electron power density shows a narrow center peak due to the finite mode wavelengths and the nonlinearly excited harmonics, which can be further enhanced by spatial or series resonances. A second peak appears above the vacuum spacer edge as f exceeds fs1 at 120 MHz because the shorter wavelengths at higher f allow secondary maxima of the surface waves to form within the reactor.

Scandium-Doped Aluminum Nitride PMUT Arrays for Wireless Ultrasonic Powering of Implantables

The present work reports on the novel usage of Scandium-doped Aluminum Nitride (AlScN) PMUT arrays for enhanced power transfer in implantable applications. Optimization considerations were explored for the PMUT array towards high performance. The transmission metric, compared to identical arrays based on Aluminum Nitride (AlN), showed a 25dB increase. Power transfer measurements also confirmed a considerable increase as compared to previous work based on AlN. Different matching strategies were explored to maximize the output power including inductor conjugate matching and matching utilizing resonators in series and parallel topologies. A full characterization of the transferred power versus incident acoustic intensity on the array revealed transmission of power levels of several milliwatts for intensities below the Food and Drug Administration’s (FDA) limit. The performance of the array, as compared with other implementations with a range of frequencies, dimensions and input acoustic intensities was bench-marked through the use of the conversion efficiency as the figure-of-merit. The practical applicability of the system, utilizing a realistic tissue phantom as the medium, was proven by interfacing with a commercially available boost converter to obtain a rectified voltage and power levels sufficient for powering and charging intra-body electronics.

Common Mode Power Control of Three-Phase Inverter for Auxiliary Load Without Access to Neutral Point

The purpose of this article is to investigate the potential of obtaining an auxiliary dc output from the common-mode switching harmonics of a three-phase inverter without access to the neutral point of the ac load. To achieve this, the control of common-mode (CM) switching harmonics with space vector modulation is proposed. With this control, CM switching harmonics can be regulated independently from the differential mode power flow to the main three-phase load. To physically implement the CM power flow, a harmonic extraction circuit is placed in parallel with the main three-phase load. The extraction circuit is formed by series-connected inductance and capacitance. Due to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> series resonance and the mutual coupling of the inductance, only common-mode switching harmonics can pass through the extraction circuit. The extracted harmonics are then rectified and delivered to the auxiliary dc output. The control and topology are verified in both simulations and experiments. In the end, it is shown in experiments that there is no significant difference of the inverter efficiency after the auxiliary dc load is connected. This method can be used for instance to drive an ac machine while charging a low voltage battery or powering a compressor simultaneously.

On Medium Frequency Differential Mode Resonance Effects in Doubly Fed Induction Machines

During synchronization phase of a doubly fed induction machine prototype abnormal high voltages were recorded at stator terminals. By evaluating the measured curves, and the frequency response of a similar machine, these overvoltages could be traced back to differential mode resonance effects within the machine itself. The effect of differential mode resonance is not restricted to doubly fed induction machines but also occurs in other machine types such as squirrel cage induction machines. If not considered in the insulation design, such abnormal voltages will lead to a premature ageing of the insulation. Depending on the operating conditions, premature failures may occur. The measured data presented in the article give an illustrative example what could happen if windings of electric machines are excited near series resonance frequency. As the occurence of this effect becomes more probable the higher the switching frequency of the converter, it is thoroughly important to be aware of it.

A Cooperative Approach of Frequency Regulation Through Virtual Inertia Control and Enhancement of Low Voltage Ride-through in DFIG-based Wind Farm

Doubly-fed induction generator (DFIG)-based wind farms (WFs) are interfaced with power electronic converters. Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario. Therefore, transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario. In this paper, a cooperative approach consisting of virtual inertia control (VIC) and a modified grid-side converter (GSC) approach for low voltage ride-through (LVRT) is proposed to achieve fault ride-through (FRT) capabilities as per the grid code requirements (GCRs) while providing frequency support to the grid through a synthetic inertia. The proposed approach provides LVRT and reactive power compensation in the system. The participation of the VIC in a rotor-side converter (RSC) provides frequency support to the DFIG-based WFs. The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario. Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults. The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter (SR-BFCL).

High-Performance Buck-Boost Partial Power Quasi-Z-Source Series Resonance Converter

Power converters are essential components of renewable energy systems. The converter efficiency decides the overall system efficiency. In a full power converter, its components process the whole input power, even if it is not mandatory. Partial power processing (PPP) is an exciting concept for improving overall system efficiency and reducing system cost and size. In PPP, the converter processes the amount of power needed to be processed. This work proposes a PPP based on the high-performance Quasi-Z-Source Series Resonance converter (QZSSRC). The proposed partial power converter belongs to the series input parallel output (SIPO) architecture. Previous publications in this area mainly consider converters with step-down voltage regulation, like the phase-shifted full-bridge converter. They underperform in this application due to operating at the maximum power when bucking the voltage the most. This paper studies two other types of dc-dc converters, buck-boost and boost, in SIPO partial power converters. Theoretical operation principles are corroborated with full experimental results given and analyzed. A 300 W prototype of the QZSSRC is used to convert the power of up to 2 kW in a PPP system with overall system efficiency values of over 99%.

Investigation into the impedance characteristics of magnetoelectric antennas

Mechanical antenna is recently considered a novel scheme for realizing very low frequency (VLF) and portable transmitters. In this paper, the impedance characteristics of 1-1 typed and 2-1 typed magnetoelectric (ME) mechanical antennas are systematically studied and compared. Based on measured frequency-impedance curves and the corresponding MBVD (Modified Butterworth-Van Dyke) model, three characteristic frequency points, i.e., the minimum impedance frequency &lt;i&gt;f&lt;sub&gt;m&lt;/sub&gt;&lt;/i&gt;, the series resonance frequency &lt;i&gt;f&lt;sub&gt;s&lt;/sub&gt;&lt;/i&gt; and the resonance frequency &lt;i&gt;f&lt;sub&gt;r&lt;/sub&gt;&lt;/i&gt; are obtained and discussed. On this basis, the influence of driving voltage, bias magnetic field, and the quality factor (Q value) on ME antenna impedance characteristics is experimentally explored. Finally, the reactance components of both 1-1 typed and 2-1 typed ME antenna are collected by referring to the actual working frequency &lt;i&gt;f&lt;sub&gt;d&lt;/sub&gt;&lt;/i&gt;. Experimental results prove that resonant ME antennas are basically pure resistive vibrators, while a ME antenna with high Q value normally fails to support high driving field because of the low resistance (&lt; 100Ω) and the strong nonlinearity. Thus, the field radiation capability in 2-1 typed ME antenna is higher than that of 1-1 typed one. This work provides perspectives for Q value selection and further optimization of a magnetoelectric antenna based on the understanding of its impedance characteristics.

High efficiency bridgeless single power conversion battery charger for electric vehicle

High efficiency chargers having high power are required to charge the batteries of light electric vehicles. This work proposes a single-power-conversion battery charger without a bridge made up of a boost AC-DC converter that is isolated and with a circuit having resonance in series to suit this need. The circuit with a series resonance decreases by offering zero current switching, you may reduce output diode recovery losses, while conduction losses associated with the input diode rectifier are reduced by using a bridgeless arrangement. Furthermore, injection of current by direct and series-resonance allows the transformer to excite the core in both directions, providing for high power capabilities (Lakshmi and Hemamalini (2019) and Haghbin et al. (2013) [1,2]). In conversion of power using single stage, the feedback linearization-derived control algorithm is also built, allowing the suggested charger for power factor correction and output power regulation. This straightforward circuit construction results in good efficiency and a large power factor. The proposed charger's ideas that are theoretical are tested in an actual setting with a 1.7 kW prototype.

Design of low phase noise K‐band VCO using high quality factor resonator in 0.18 μm CMOS technology

A novel resonator to improve the phase noise of a Voltage-Controlled Oscillator (VCO) utilizing double series resonances or two attenuation zeros to improve the susceptance slope parameter of the resonator circuit is proposed, and its effectiveness is demonstrated by designing a low phase noise K-band VCO. The first series resonance is created by an additional inductor (L) in series to the capacitor (C) in the parallel branch of a conventional LC-tank circuit, and the second one is realized by an additional capacitor in series to the whole resonator circuit. The additional L is realized by defected ground structures (DGS) so that there is no additional burden in the chip size. The proposed resonator is fabricated in 0.18 μm CMOS technology and has active quality factor of 101 and a compact size of 0.009 mm2 (0.00046 λ2). The measured return loss |S11| and insertion loss |S21| of the fabricated prototype resonator are 2.8 and 11 dB, respectively, at a center frequency of 37 GHz with 8 GHz of bandwidth. The resulting active quality (QK-) factor of the proposed resonator is enhanced significantly that, in returns, improves the phase noise. The design is implemented in 0.18 μm CMOS technology, and the post-layout simulation shows that VCO has a tuning range of 3.8% and phase noise of −114.4 dBc/Hz @1 MHz offset at 19.5 GHz oscillation. The VCO consumes 2.96 mW power resulting in a Figure of Merit (FoM) of −195.5 dB. The proposed resonators improve the VCO FoM by more than 5.5 dB compared to conventional LC resonator.

Integrated Microwave Photonic Spectral Shaping For Linearization and Spurious-Free Dynamic Range Enhancement

Integrated microwave photonics (MWP) is a fast growing area where high frequency microwave signals are processed in the optical domain, merging key advantages of both microwave photonics and photonic integrated circuits (PICs) technologies including low-loss, reconfigurability, advanced functionality, enhanced stability, and reduced footprint. Plenty of functionalities have been demonstrated in integrated MWP, especially based on spectral shaping technique, where the phase and amplitude of the optical spectrum is precisely tailored by PICs. However, on-chip linearization is lagging behind and has not been investigated deeply. It is crucial and urgent to study on-chip linearization methods, which will lead to advanced integrated MWP systems with large spurious-free dynamic range (SFDR). In this paper, we present two novel techniques for on-chip linearization of microwave photonic links. The first technique is based on line-by-line complex spectral shaping using a series of ring resonators. The second technique relies on spatial separation to achieve parallel spectral shaping in two complementary spatial channels. Both methods are demonstrated in low-loss programmable silicon nitride circuits that can already host a number of advanced functionalities. Our results point to the great potential of integrating advanced functionalities and linearization in the same integrated platform.

Breakdown Characteristics of Long Air Gap at Different Frequency Based on Series Resonance

In today’s rapid economic development, with the development of science and technology, higher requirements have been put forward in the economic operation of the system. This requires various departments to make more reasonable use of existing energy and equipment, and to ensure quality. Meet all aspects of supply with more energy-saving and more economical operation methods. Therefore, more and more attention has been paid to the research on the method of predicting the breakdown voltage of the air gap. Although domestic and foreign scholars have used power frequency test transformers to carry out a large number of long air gap experimental researches, the research on the breakdown voltage of long air gaps based on the principle of vector machines is still blank. In this paper, a vector machine test device is used to study the breakdown discharge characteristics of a long air gap at two frequencies of 229Hz and 68Hz. Comparing the test phenomena at different frequencies, it is found that the initial discharge voltage of the streamer corona is lower when the frequency is 229Hz, and the discharge phenomenon before breakdown is more intense, and the quality factor will be significantly reduced due to the violent discharge. At the same time, under the same test conditions, the breakdown voltage at 229Hz is lower than that at 68Hz, and as the air gap increases, the difference between the two is greater. The experimental results show that the breakdown voltage of the long air gap based on the vector machine is different when the frequency is different, and the safety distance of the field withstand voltage test should be evaluated according to the experimental data under the vector machine condition to ensure the safety of the test.

A Multiband VCO Using a Switched Series Resonance for Fine Frequency Tuning Sensitivity and Phase Noise Improvement

This work proposes a new technique to reduce the phase noise (PN) and improve the tuning sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -band voltage-controlled oscillators (VCOs) by increasing the quality ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -) factor of the switched resonator. The proposed switched resonator consists of a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor half-circle inductor in parallel with an improved switched varactor and operates in four different frequency bands using a single switching voltage pin. The proposed switched resonator introduces one pole before the parallel resonance frequency, which sharpens the skirt characteristics of the scattering parameters of the resonator. The chip is implemented in the 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS technology, and the proposed VCO operates in four different frequency bands, with a total frequency tuning range (FTR) of 10.7%. The first band ranges from 19.4 to 19.84 GHz, the second band ranges from 19.8 to 20.3 GHz, the third band ranges from 20.25 to 20.73 GHz, and the fourth band ranges from 20.7 to 21.3 GHz. The VCO core circuit draws a dc current of 5 mA from a 1.8-V supply and achieves a PN of −110.7 at 1-MHz offset from a 20.25-GHz carrier. This proposed oscillator achieved a figure of merit (FoM) of −186.8 dBc/Hz, while the FoM taking account of the tuning voltage (FoM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T/V</sup> ) is −181.4 dBc/Hz.