Common-mode Noise Cancellation Research Articles

Research on Symmetrical Integrated Matrix Transformer Applied to Full-Bridge LLC Resonant Converter for CM Noise Cancellation

The planar transformer is widely used in DC-DC power converters due to the small leakage inductance and low height. However, the big overlapping area between primary and secondary windings in the planar transformer generates large parasitic capacitance, which brings serious common-mode (CM) noise problems. The full-bridge LLC resonant converter can meet the premise of CM noise cancellation since the noise sources on the primary and secondary sides have same magnitudes and opposite phases. Therefore, the symmetrical planar transformer design is more conducive to the attenuation of CM noise. This paper analyses symmetrical winding arrangements with minimal winding loss for the transformer in the full-bridge LLC resonant converter. Based on this, the symmetry of the reverse integrated matrix transformer (RIMT) and forward integrated matrix transformer (FIMT) composed of two elemental transformers is investigated. The scattering parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> is used to evaluate the symmetry of RIMT and FIMT. It is found that the two CM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> curves of RIMT are not consistent even though the windings have been arranged symmetrically. In contrast, the CM <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> curves for FIMT are almost overlapped. This implies that FIMT is symmetrical and capable of CM current cancellation. Finally, the CM noises of the full-bridge LLC resonant converter using RIMT, RIMT with a balance capacitor, and FIMT are tested. Experimental results show that the CM noise for the converter using FIMT is lowest. Especially at the switching frequency, the CM noise is reduced by more than 20 dBμV.

Fiber-Coupled Diamond Magnetometry with an Unshielded Sensitivity of 30pT/Hz

Ensembles of nitrogen-vacancy centers (NVCs) in diamond can be employed for sensitive magnetometry. In this work, we present a fiber-coupled NVC magnetometer with an unshielded sensitivity of $(30\ifmmode\pm\else\textpm\fi{}10)\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in a (10--500)-Hz frequency range. This sensitivity is enabled by a relatively high green-to-red photon conversion efficiency, the use of a [100] bias-field alignment, microwave and lock-in amplifier (LIA) parameter optimization, as well as a balanced hyperfine-excitation scheme. Furthermore, a silicon carbide ($\mathrm{SiC}$) heat spreader is used for microwave delivery, alongside low-strain 1-${\mathrm{mm}}^{3}{\phantom{\rule{0.2em}{0ex}}}^{12}$$\mathrm{C}$ diamonds, one of which is placed in a second magnetically insensitive fluorescence-collecting sensor head for common-mode noise cancellation. The magnetometer is capable of detecting signals from sources such as a vacuum pump up to 2 m away, with some orientation dependence but no complete dead zones, demonstrating its potential for use in remote-sensing applications.

Non-Isolated DC-DC Converters With Low Common-Mode Noise by Using Split-Winding Configuration

The common-mode (CM) noise in nonisolated dc-dc converters is mainly caused by the displacement current through the high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> node in the circuit and the associated parasitic capacitance, and it may cause electromagnetic interference (EMI) to the surrounding equipments. To reduce the original CM noise and shrink the EMI filter size of non-isolated dc-dc converters, CM noise cancellation methods have been proposed, including the symmetry circuit, balancing technique, passive cancellation and CM voltage cancellation. In these methods, additional components or windings are required for reducing the CM noise. In this article, a new CM noise cancellation method in non-isolated dc–dc converters is proposed by adopting a split-winding configuration. Compared to the existing CM noise cancellation methods which require additional components, the proposed method in the buck, boost and single-ended primary-inductor converter (SEPIC) converters which runs in voltage step-up mode has the identical volume as their conventional circuit configurations. The proposed method is verified for a buck converter by experiment.

Sensing and Cancellation Circuits for Mitigating EMI-Related Common Mode Noise in High-Speed PAM-4 Transmitter

The common mode (CM) current in differential circuits generates CM noise which radiates in the environment and causes electromagnetic interference (EMI) with electronic devices in proximity. This noise is generated due to imbalance in the charging and discharging paths of the driver circuit and asymmetric equalization. A systematic study of how asymmetric equalizer increase the CM noise is still lacking. Few active on-chip solutions are proposed for wireline transmitters up to 20-Gbps speed. However, these solution does not suppress CM noise by the equalizer and they could not support four-level pulse amplitude modulation (PAM-4) optical transmitters. This paper analyzes two potential sources of EMI-related CM noise, the common mode logic (CML) driver and feed forward equalization (FFE) circuit, and presents a novel on-chip active circuit technique for automatic CM noise cancellation in high-speed PAM-4 transmitter. This solution provides the benefits of small size and low cost by eliminating the need for discrete components to suppress EMI. The post-layout simulation demonstrates that the CM noise cancellation circuit (CMNC) efficiently mitigate the EMI by suppressing the CM noise up to 90% and consumes 5 mW, with core area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17 \mu m \times 9 \mu m$ </tex-math></inline-formula> .

Common-Mode Current Reduction at DC and AC Sides in Inverter Systems by Passive Cancellation

It is well known that PWM inverters generate common-mode (CM) voltages, which may cause the CM electromagnetic interference and leakage current in the applications such as photovoltaic or motor drive systems. The CM noise issue becomes more severe with the application of silicon-carbide devices, which have higher dv/dt than silicon devices. In this article, a passive cancellation method is proposed by inserting two CM transformers (CMT) into the input and output side of the inverter, respectively. The selection of the turns ratio for two CMTs is analyzed and revealed to achieve the best CM noise cancellation, and the influence of the parasitics in the CMT is investigated as they limit the bandwidth for CM noise cancellation. Compared to the passive filter, floating filter, and the active cancellation method, the proposed method could reduce the CM noise at both sides simultaneously regardless of the CM impedance of the source or the load. A single-phase inverter is built, and the proposed method achieves 40 dB reduction at both sides, which verifies the effectiveness of the proposed method.

Common-Mode Voltage Cancellation for Reducing the Common-Mode Noise in DC–DC Converters

Common-mode (CM) noise cancellation method is an attractive approach to reduce the original CM noise in power converters, which helps to shrink the size of electromagnetic interference filter. Traditional CM noise cancellation method cancels the CM noise current by adding a branch consisted of a compensation voltage source and a compensation capacitor, which generates a cancellation current and nullifies the noise current. As the duality, the voltage cancellation method is also feasible for reducing the CM noise, which has not been investigated in dc–dc converters. In this article, a common-mode voltage cancellation (CMVC) method is proposed, which cancels the CM voltage of the converter by inserting compensation voltage source into the input power cord. The requirement for achieving CMVC is that the cancellation voltage and the parasitic capacitances in the circuit are matched. The applications of CMVC method in basic nonisolated and isolated dc–dc converters are presented, and the considerations for practical applications of this method are discussed. Finally, a buck converter and a half-bridge LLC resonant converter prototype are built, and the proposed method is verified by experiment, respectively.

All-polarization-maintaining, polarization-multiplexed, dual-comb fiber laser with a nonlinear amplifying loop mirror.

We developed an all-polarization-maintaining, polarization-multiplexed, dual-comb fiber laser with a nonlinear amplifying loop mirror (NALM) mode-locking mechanism. Owing to the use of the slow and fast axes of a polarization-maintaining fiber (PMF), the dual-frequency combs with slightly different repetition rates from the single-laser cavity are generated at the same center wavelength without extra-cavity nonlinear spectral broadening. The narrow relative beat note between the two frequency combs is obtained with a full-width-at-half-maximum of ~1 kHz in the optical frequency domain. The two frequency combs have high relative stability and mutual coherence owing to passive common-mode noise cancellation.

Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300600 and 2016YFA0301500), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07030000), and the National Natural Science Foundation of China (Grant No. 11474347).

A miniature quad-channel optically pumped atomic magnetometer (OPM) has been developed based on the spin-exchange relaxation-free (SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography (MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz1/2, which is also good enough for MEG measurement. The vapor cell is heated to 160 °C by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.

High-coherence ultra-broadband bidirectional dual-comb fiber laser.

Dual-comb spectroscopy has emerged as an attractive spectroscopic tool for high-speed, high-resolution, and high-sensitivity broadband spectroscopy. It exhibits certain advantages when compared to the conventional Fourier-transform spectroscopy. However, the high cost of the conventional system, which is based on two mode-locked lasers and a complex servo system with a common single-frequency laser, limits the applicability of the dual-comb spectroscopy system. In this study, we overcame this problem with a bidirectional dual-comb fiber laser that generates two high-coherence ultra-broadband frequency combs with slightly different repetition rates (frep). The two direct outputs from the single-laser cavity displayed broad spectra of > 50 nm; moreover, an excessively small difference in the repetition rate (< 1.5 Hz) was achieved with high relative stability, owing to passive common-mode noise cancellation. With this slight difference in the repetition rate, the applicable optical spectral bandwidth in dual-comb spectroscopy could attain ~479 THz (~3,888 nm). In addition, we successfully generated high-coherence ultra-broadband frequency combs via nonlinear spectral broadening and detected high signal-to-noise-ratio carrier-envelope offset frequency (fCEO) beat signals using the self-referencing technique. We also demonstrated the high relative stability between the two fCEO beat signals and tunability. To our knowledge, this is the first demonstration of fCEO detection and frequency measurement using a self-referencing technique for a dual-comb fiber laser. The developed high-coherence ultra-broadband dual-comb fiber laser with capability of fCEO detection is likely to be a highly effective tool in practical, high-sensitivity, ultra-broadband applications.

Evaluation Method of Flyback Converter Behaviors on Common-Mode Noise

Common-mode (CM) conduction electromagnetic interference (EMI) is a challenge for switched-mode power supply (SMPS) designers. A flyback converter is a traditional topology used in low-power isolated applications. The size and cost of EMI filters are important considerations for higher power density and lower cost of SMPS design. In most cases, the CM current is generated by voltage pulsation (dv/dt) assigned on the primary winding and the secondary winding. The CM current conduction paths can be mainly categorized into two categories. One is the interwinding parasitic capacitance of the transformer, and the other is the parasitic capacitance between the semiconductor switches and the protective ground. This paper proposed an evaluation method to measure the equivalent CM noise capacitance of the two main CM current conduction paths, respectively. Then, this paper proposed a CM noise cancellation scheme based on the transformer winding design combining the measurement technique and the FEM simulation tool. Planar transformers with PCB windings also have advantages in low profile, good heat dissipation, and good stray parameter consistency. Based on these considerations, an 18-W adapter is designed and tested to verify the effectiveness of the proposed evaluation method and the design scheme.

Mechanical characterisation of the TorPeDO: a low frequency gravitational force sensor

Newtonian noise is likely to be a future challenge at low frequencies for Advanced LIGO and other second generation gravitational wave detectors. We present the TorPeDO system: a dual torsion pendulum sensor designed to measure local gravitational forces to high precision. Gravitational forces induce a differential rotation between the two torsion beams, which is measured with an optical read-out. Both torsion pendulums have a common suspension point, tunable centre of mass, and resonant frequency. This produces a high level of mechanical common mode noise cancellation. We report on a controls prototype of the TorPeDO system, presenting the frequency response and tuning range of both pendulums. A noise budget and mechanical cross-coupling model for this system are also presented. We demonstrate frequency tuning of the two torsion pendulums to a difference of 4.3 μHz.

A microfabricated optically-pumped magnetic gradiometer.

We report on the development of a microfabricated atomic magnetic gradiometer based on optical spectroscopy of alkali atoms in the vapor phase. The gradiometer, which operates in the spin-exchange relaxation free regime, has a length of 60 mm and cross sectional diameter of 12 mm, and consists of two chip-scale atomic magnetometers which are interrogated by a common laser light. The sensor can measure differences in magnetic fields, over a 20 mm baseline, of 10 fT/[Formula: see text] at frequencies above 20 Hz. The maximum rejection of magnetic field noise is 1000 at 10 Hz. By use of a set of compensation coils wrapped around the sensor, we also measure the sensor sensitivity at several external bias field strengths up to 150 mG. This device is useful for applications that require both sensitive gradient field information and high common-mode noise cancellation.

Common-Mode Noise Cancellation by an Antiphase Winding in Multilayer Isolated Planar Transformer

Common-mode (CM) noise is always present in switch-mode power supplies. All International Electrical Commission class I appliances must have their chassis directly connected to the earth ground, which provides a low impedance path for CM noise to transfer from primary to secondary via the isolated transformer. A proposed planar transformer construction is analyzed and a comparison of CM noise cancellation performance with wire-wound transformers is presented. Planar transformers are found to have better noise cancellation throughout the conducted electromagnetic interference range, thanks to a better winding plane matching to the primary CM noise source winding plane. A planar transformer with two primary winding planes is investigated and a construction with antiphase winding is proposed for best CM noise attenuation.

Common-Mode Noise Cancellation in Switching-Mode Power Supplies Using an Equipotential Transformer Modeling Technique

Electromagnetic interference (EMI) is a significant challenge in the design of high-efficiency switching-mode power supplies due to the presence of common-mode (CM) noise. In many power-supply designs, a variety of noise suppression schemes must be implemented in order to meet EMI requirements. Most of these schemes create power loss that lead to efficiency and thermal issues. In this paper, a transformer construction technique is proposed that effectively reduces the CM noise current injecting across the isolated primary and secondary windings. This technique is based on the zero equipotential line theory. A transformer design with the proposed CM noise cancellation technique can achieve high conversion efficiency as well as substantial CM noise rejection.

Reliable design of digitally programmable gain amplifier for ultrasound diagnostic applications

This paper presents a reliable design of programmable gain amplifier suitable for medical ultrasound applications that has distinguishing features. First, it has a precise digitally programmable voltage gain which is set by a binary code without a need to adjust any external resistor. Second, it has a wide bandwidth independent of adjusted gain. Third, it has single element control of its gain and this element has no impact on the amplifier bandwidth which results in a flexible gain setting. Fourth, it has very low output noise voltage spectral density (less than 10 nV/√Hz for frequencies higher than 1 MHz). Fifth, it has fully symmetrical differential inputs that provide cancellation of CFA input offset and common-mode noise. Last, its gain and bandwidth are optimised for proper use in ultrasound diagnostic applications.

Sub-μHz MOSFET 1/f noise measurements

The 1/f noise in integrated NMOS transistors at sub-μHz frequencies was measured by developing a simple and inexpensive common-mode noise-cancellation technique to attenuate the effects of temperature fluctuations. The noise has a power-law spectrum with slope −1.2 and an approximately Gaussian amplitude distribution.

Dual-frequency Brillouin fiber laser for optical generation of tunable low-noise radio frequency/microwave frequency

We demonstrate a new approach, i.e., a cw dual-frequency Brillouin fiber laser pumped by two independent single-frequency Er-doped fiber lasers, for the generation of tunable low-noise rf/microwave optical signals. Its inherent features of both linewidth narrowing effect in a Brillouin fiber cavity and common mode noise cancellation between two laser modes sharing a common cavity allow us to achieve high frequency stability without using a supercavity. Beat frequency of the dual-frequency Brillouin fiber laser can be tuned from tens of megahertz up to 100 GHz by thermally tuning the wavelengths of the two pump lasers with tuning sensitivity of approximately 1.4 GHz/ degrees C. Allan variance measurements show the beat signals have the hertz-level frequency stability.

Modulation-dependent limits to intensity-noise suppression in microwave-photonic links

Cancellation of common-mode intensity noise in microwave-photonic links is found to be limited by the applied intensity modulation. A model is developed and verified experimentally for the dependence of the maximum noise suppression on modulation index, for two-tone and multichannel modulation. For example, for a root-mean-square modulation index of 0.3, suppression is limited to 5 dB.

Differentially-Tuned VCO with Reduced Tuning Sensitivity and Flicker Noise Up-Conversion

Differential tuning in oscillators allows cancellation of common-mode bias noise and lower tuning sensitivity with respect to the most conventional single-ended tuning. However, the direct application of differential tuning increases the capacitor non-linearity and the flicker-induced phase noise. This paper analyzes quantitatively this phenomenon and proposes a novel configuration, which includes all the benefits of differential tuning with no penalty on phase noise. This circuit is fabricated in a 0.35-?m CMOS technology together with a single-end-tuned oscillator and both cover the 2.0--2.4 GHz frequency range. The measured 1/f3 phase noise at 10 kHz offset is ?71 dBc/Hz, which outperforms the companion single-end tuning oscillator by 10 dB.

A novel common-mode noise cancellation technique for VDSL applications

Very-high-speed digital subscriber loop modems operate in frequency bands which coincide with many significant radio-frequency interference sources, particularly commercial AM radio. In these bands, the balance of most twisted-pair cables is low enough to allow substantial interference to transfer via the differential mode, disrupting the transmitted information signal. A novel wideband common-mode noise cancellation technique is presented. Simulation results show that the common-mode noise cancellation technique could provide 20- to 30 dB improvement in those radio frequency bands. Construction and testing of a hardware prototype are also presented. With finite-precision effects, measured test results show that common-mode noise cancellation in the order of 15-20 dB is achievable.