Common-mode Noise Suppression Research Articles

Capacitively Coupled Electrocardiogram Measuring System and Noise Reduction by Singular Spectrum Analysis

A wearable electrocardiogram (ECG) measuring system is designed based upon capacitively coupled biopotential sensing electrodes. The sensing electrodes are made from the standard printed-circuit board. Using a reversely connected diode to provide the required high-value bias resistance, the pickup circuit for biopotential sensing is implemented by a high-input-impedance instrumentation amplifier. Two different configurations of the ECG measuring system are constructed and experimentally tested. One is a floating ground configuration in which only two sensing electrodes are used for ECG signal acquisition. Another is the passive ground configuration in which an additional grounding electrode is employed as the reference for common-mode noise suppression. The ECG signal can be obtained through thin clothes for both cases but performs lower signal-to-noise ratio. In order to improve the quality of the obtained signal, an algorithm based on a singular spectrum analysis is designed for noise reduction. A matching template is introduced to pick out the critical principal components automatically. Experimental results show that, with the aid of the proposed algorithm, satisfied ECG and respiration signals can be effectively obtained outside cotton-fiber clothing.

Periodically Corrugated Reference Planes for Common-Mode Noise Suppression in High-Speed Differential Signals

We present a new scheme using a periodically corrugated reference plane (PCRP) for wideband suppression of a common mode (CM) noise in high-speed differential signals. In the PCRP, the CM return current path is designed to have a stepped impedance profile; thus, inducing the stopband for the CM noise. To analyze the CM noise suppression of the PCRP, an analytic dispersion equation is derived and verified by the full-wave simulation results and measurements. The PCRP experimentally demonstrates the CM noise suppression over the wideband frequency range from 5.3 to 10.4 GHz. In addition, good signal integrity characteristics for odd-mode propagation are verified by the measurements of the differential insertion loss and the eye diagram.

A Bidirectional Neural Interface Circuit With Active Stimulation Artifact Cancellation and Cross-Channel Common-Mode Noise Suppression

This work presents a bidirectional neural interface circuit that enables simultaneous recording and stimulation with a stimulation artifact cancellation circuit. The system employs a common average referencing (CAR) front-end circuit to suppress cross-channel environmental noise to further facilitate use in clinical environment. This paper also introduces a new range-adapting (RA) SAR ADC to lower the system power consumption. A prototype is fabricated in $0.18\;\mu {\rm{m}}$ CMOS and characterized and tested in vivo in an epileptic rat model. The prototype attenuates stimulation artifacts by up to 42 dB and suppresses cross-channel noise by up to 39.8 dB. The measured power consumption per channel is 330 nW, while the area per channel is 0.17 mm $^2$ .

Dual-Band Balanced Bandpass Filter With Common-Mode Suppression Based on Electrically Small Planar Resonators

The design of fully planar dual-band balanced bandpass filters with common-mode noise suppression is reported. The proposed filters are based on electrically small resonators coupled through admittance inverters. For design purposes, the circuit models of the considered resonators are reported. The key aspect for selective mode suppression (i.e., common-mode rejection in the differential-mode pass bands) is related to symmetry properties. Thus, for the differential-mode the symmetry plane is an electric wall, and the equivalent circuit for that mode provides dual-band functionality. Conversely, for the common-mode the symmetry plane is a magnetic wall, and the equivalent circuit exhibits a rejection band. As a proof of concept, the design of an order-2 Chebyshev dual-band balanced bandpass filter with center frequencies $f_{1} = 1.8$ GHz (GSM band) and $f_{2}= 2.4$ GHz (Wi-Fi band), fractional bandwidth $FBW = 7 \%$ , and ripple level $L_{Ar}= 0.01$ dB is reported.

Magnetic tensor gradiometry using Ramsey interferometry of spinor condensates

We have realized a magnetic tensor gradiometer by interferometrically measuring the relative phase between two spatially separated Bose-Einstein condensates (BECs). We perform simultaneous Ramsey interferometry of the proximate $^{87}$Rb spin-1 condensates in freefall and infer their relative Larmor phase -- and thus the differential magnetic field strength -- with a common-mode phase noise suppression exceeding $50\,\mathrm{dB}$. By appropriately biasing the magnetic field and separating the BECs along orthogonal directions, we measure the magnetic field gradient tensor of ambient and applied magnetic fields with a nominal precision of $30\,\mathrm{\mu G\,cm^{-1}}$ and a sensor volume of $2\times10^{-5}\,\mathrm{mm}^3$. We predict a spin-projection noise limited magnetic energy resolution of order $\hbar$ for typical Zeeman coherence times of trapped condensates with this scheme, even with the low measurement duty cycle inherent to BEC experiments.

Ultra-Compact (80 <formula formulatype="inline"> <tex Notation="TeX">${\hbox{mm}}^{2}$</tex></formula>) Differential-Mode Ultra-Wideband (UWB) Bandpass Filters With Common-Mode Noise Suppression

This paper presents a novel approach for the implementation of balanced ultra-wideband (UWB) bandpass filters with common-mode noise suppression. To a first-order approximation, the differential-mode filter response is described by the canonical circuit model of a bandpass filter, i.e., a cascade of series-connected resonators alternating with shunt-connected parallel resonant tanks. Thus, the series branches of the balanced filter are implemented by means of inductive strips and patch capacitors, whereas the shunt sections are realized through mirrored stepped-impedance resonators (SIRs) and low-impedance (i.e., capacitive) short transmission-line sections. For the differential mode, the symmetry plane is a virtual ground, the wide strip sections of the SIRs are effectively grounded, and the SIRs behave as grounded inductors parallel connected to capacitors. However, for the common mode, where the symmetry plane is an open (magnetic wall), the SIRs act as shunt-connected series resonators, thus providing transmission zeros at their resonance frequencies. By properly tailoring the location of these transmission zeros, rejection of the common mode over the differential filter passband can be achieved. To illustrate the potential of the approach, an order-5 balanced bandpass filter covering the regulated band for UWB communications (3.1-10.6 GHz) is designed and fabricated. The filter exhibits common-mode rejection above 10 dB over the whole differential filter passband, with differential-mode insertion losses lower than 1.9 dB and return losses better than 10 dB. Since the proposed design approach is based on planar semi-lumped components, filter size is as small as 10.5 mm × 7.6 mm.

A broad stopband common-mode suppression defected ground structure filter with complementary structure

A low-cost defected ground structure (DGS) wideband stopband filter adopting complementary structure is proposed, which is designed for common-mode noise suppression in high-speed differential signals. The filter is etched below the low cost FR4 printed circuit board. To avoid stimulating the common-mode noise, the DGS cells on ground planes are kept symmetrical to the central line of the two differential signal lines. Both sides of the filter adopt a symmetric cup-shape DGS structure and the middle of the filter adopts a symmetric umbrella-type structure. All of the DGS structures are complementary, which makes the filter compact and miniaturized. What is more, because the spaces among the three DGS are closer, there exist the mutual inductances among them, which are utilized to achieve a wide stopband filter. The simulated result demonstrates the proposed filter has a wideband bandwidth of 6.8 GHz over 20 dB. In order to analyze the effect of compact structure of the filter, a filter having the same DGS patterns but large spaces among them is compared with it. The simulated result demonstrates that the stopband bandwidth of the compared filter has a wideband bandwidth of 4.4 GHz over 20 dB, of which the bandwidth is about 2.4 GHz less than that of the proposed filter. It is obvious that there exists a mutual inductance in the compact DGS structure common-mode filter, which plays an important role in broadening the bandwidth of the proposed filter. In order to facilitate analysis, an equivalent model of LC circuit is also given. The equivalent parameters of LC can be deduced from the definition of 3 dB cut-off frequency and resonant frequency, of which the values can be obtained by the HFSS simulation. The simulated and measured results show that the differential signal under the DGS filter is nearly intact, and the common-mode noise can be reduced over 20 dB from 4.6 GHz to 11.4 GHz and over 15 dB from 4.3 GHz to 12 GHz, while the area of the filter is only 10 mm by 10 mm. Compared with the periodic DGS at the same suppression depth of common-mode noise over 20 dB, the method has the advantages that surface area is reduced to no more than 30%, and the stopband width is increased by over 50%.

A low-noise and fast pre-amplifier and readout system for SiPMs

To operate silicon photomultipliers (SiPMs) in a demanding environment with large temperature gradients, different amplifier concepts were characterized by analyzing SiPM pulse-shapes and charge distributions. A fully differential 4-wire SiPM pre-amplifier with separated tracks for the bias voltage and with good common-mode noise suppression was developed and successfully tested. To achieve highest single-pixel resolutions an online after-pulse and pile-up suppression was realized with fast readout electronics based on digital filters.

Wavelength modulation spectroscopy with signal–reference beam method for highly sensitive gas detection

Wavelength modulation spectroscopy combined with signal–reference beam method is used for trace gas detection. The developed technique combines the advantages of common-mode noise suppression and signal-to-noise ratio improvement. The performance of the resulting water vapor sensor is markedly improved because of scanning baseline suppression, effective suppression of the target gas content in the components and resistance to external factors such as temperature and humidity. Trace water vapor detection experiments verify that the measurement accuracy of the system can reach 1 ppmv for an optical path length of 10 cm.

Phase-sensitive optical coherence tomography using an Vernier-tuned distributed Bragg reflector swept laser in the mouse middle ear.

Phase-sensitive optical coherence tomography (PhOCT) offers exquisite sensitivity to mechanical vibration in biological tissues. There is growing interest in using PhOCT for imaging the nanometer scale vibrations of the ear in animal models of hearing disorders. Swept-source-based systems offer fast acquisition speeds, suppression of common mode noise via balanced detection, and good signal roll-off. However, achieving high phase stability is difficult due to nonlinear laser sweeps and trigger jitter in a typical swept laser source. Here, we report on the initial application of a Vernier-tuned distributed Bragg reflector (VT-DBR) swept laser as the source for a fiber-based PhOCT system. The VT-DBR swept laser is electronically tuned and precisely controls sweeps without mechanical movement, resulting in highly linear sweeps with high wavelength stability and repeatability. We experimentally measured a phase sensitivity of 0.4 pm standard deviation, within a factor of less than 2 of the computed shot-noise limit. We further demonstrated the system by making ex vivo measurements of the vibrations of the mouse middle ear structures.

RESEARCH COMMON MODE REJECTION IN CONDUCTOMETRIC BIOSENSOR SYSTEM WITH DIFFERENTIAL SENSORS

In the article are given theoretical and experimental evaluation of errors which arise due to incomplete suppression of common-mode noise on a differential sensor. The improved scheme of the measuring channel is suggested, its conversion feature studied and the possibility of diagnostic sensors is demonstrated. With using vector models evaluated the suppression of common mode noise for different pairs of transducer's parameters. Experimental confirmation of the theoretical estimates of possible levels of errors from common mode noise in the experimental measurement channels is given.

A Comprehensive Investigation of a Common-Mode Filter for Gigahertz Differential Signals Using Quarter-Wavelength Resonators

This paper presents a comprehensive investigation on an inexpensive and wideband common-mode noise suppression filter that uses a quarter-wavelength resonator. An equivalent transmission line model is also used to evaluate the effectiveness of the proposed structure in a common-mode filter (CMF). Moreover, more important parameters, such as coupling coefficients are presented to investigate the characteristics of CMF unit. The performance of CMF is then characterized using two coupling coefficients between two differential traces and between differential traces and a quarter-wavelength resonator. A simple design approach is also presented for a wideband CMF. Numerical results demonstrate that CMF with three different lengths of quarter-wavelength resonators have rejection bands of 3.94-8.74 GHz and 3.53-10.1 GHz at cutoff frequencies of -20 dB and -10 dB, respectively Time-domain common-mode noise is decreased by approximately 60%. Moreover, analyses of differential insertion loss and group delay indicate that the differential signals maintain sufficient signal integrity when the wideband CMF is used in single- and two-pair differential interconnects. Finally, CMF is validated by an eye diagram and by measurements of time/frequency-domain common-mode noise and I/O cable common-mode current.

Application of VSI-EBG Structure to High-Speed Differential Signals for Wideband Suppression of Common-Mode Noise

In this paper, we present wideband common-mode (CM) noise suppression using a vertical stepped impedance electromagnetic bandgap (VSI-EBG) structure for high-speed differential signals in multilayer printed circuit boards. This technique is an original design that enables us to apply the VSI-EBG structure to differential signals without sacrificing the differential characteristics. In addition, the analytical dispersion equations for the bandgap prediction of the CM propagation in the VSI-EBG structure are extracted, and the closed-form expressions for the bandgap cutoff frequencies are derived. Based on the dispersion equations, the effects of the impedance ratio, the EBG patch length, and via inductances on the bandgap of the VSI-EBG structure for differential signals are thoroughly examined. The proposed dispersion equations are verified through agreement with the full-wave simulation results. It is experimentally demonstrated that the proposed VSI-EBG structure for differential signaling suppresses the CM noise in the wideband frequency range without degrading the differential characteristics.

The Study for Common Mode Noise Suppression in Measuring Equipment Calibration

The application of a variety of high-tech equipment, greatly improve the execute effectiveness of the equipment system. It plays a decisive role that internal parameters of the device is accurate or not, for the normal function used of these complex instrument systems. The importance of maintenance and calibration process for the test equipments accuracy must be reliable and accurate is increasingly obvious. The common mode noise suppression in equipment measurement and testing process is often encountered and must be solved in related field.

Realization of autofocusing system for laser direct writing on non-planar surfaces

This paper presents an autofocusing system for laser direct writing on non-planar surfaces, including focus error signal detection and focusing control. The focus error signal detection is based on modified confocal techniques, which features easy implementation, independence of the tilt angles of non-planar surfaces, and excellent suppression of common-mode noise or variable system factors. We also present a macro/micro dual-drive mechanism and its synchronous operation for focusing control on non-planar surfaces. Finally, a performance evaluation of the autofocusing system is presented. The uniform line width of 2.1 μm for a pattern on a convex spherical substrate with a curvature radius of 100 mm shows the autofocusing system performs well.

Dynamic scan detection of focal spot on nonplanar surfaces: theoretical analysis and realization

A new approach called dynamic-scan-detection is presented to detect the focal spot on nonplanar surfaces, which is a key technique for laser direct writing on nonplanar surfaces. From the depth response properties of a confocal system on a nonplanar surface, the approach scans the axial shift of intensity response peak by oscillating the modified pinhole in the axial direction, and demodulates the defocus by measuring the length of time between two peaks of measured intensity waveform in one period. Compared with conventional methods, this approach features easy implementation, wide depth measurement range without deterioration of the depth discrimination property, dynamically adjustable scan amplitude, and more importantly, suppression of common-mode noise or variable system factors.

A Broadband and Miniaturized Common-Mode Filter for Gigahertz Differential Signals Based on Negative-Permittivity Metamaterials

A novel wideband and miniaturized common-mode noise suppression filter is proposed based on the concept of an effective negative-permittivity metamaterial (MM) transmission line (TL). The propagation properties for the odd and even modes in the proposed structure are derived from the TL theory and Bloch theorem. Two- and four-port equivalent-circuit models are developed to explain the common-mode suppression characteristics. The dispersion relation has a good agreement with the full-wave simulation and measurement result. Based on the low-temperature co-fired ceramic fabrication technology, miniaturized common-mode filters with four and eight cells are realized using the concept of the effective negative-permittivity MM. For the four-cell structure, the filter size is 0.16 ¿g × 0.26 ¿g with the corresponding real size of 3.2 mm × 5.12 mm. It is found that the common-mode noise can be reduced over 10 dB from 3.8 to 7.1 GHz with the fractional bandwidth of 60% in the frequency domain, and is reduced over 50% for voltage amplitude in the time domain. More importantly, the differential signal integrity, in terms of insertion loss and group delay in the frequency domain and eye diagrams in the time domain, is not degraded within the wide stopband. To our best knowledge, it is the first broadband common-mode filter designed for gigahertz differential signals based on the concept of MM TL with most compact size.

A Novel Wideband Common-Mode Suppression Filter for Gigahertz Differential Signals Using Coupled Patterned Ground Structure

A wideband and compact filter design for common-mode noise suppression in high-speed differential signals is proposed based on two U-shaped and one H-shaped coupled patterned ground structure. An equivalent model of three coupled LC resonators to predict the common-mode suppression characteristics is also developed with good agreement to the full-wave simulation and measurement result. A test sample is designed and fabricated on a standard printed circuit board (PCB). It is found the common-mode noise can be reduced by the filter over 15 dB from 3.6 to 9.1 GHz and over 75% of amplitude in the time domain. More important, the differential signal integrity, in terms of insertion loss and group delay in the frequency domain and eye diagrams in the time domain, is not degraded within the wide bandwidth. The fractional bandwidth of the stopband can reach 87% and the filter size is about 0.44 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> times 0.44 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> . The radiation caused by the common-mode current on the attached I/O cables is also efficiently suppressed by 10 dB on average within the designed stopband. To our best knowledge, it is the first low-cost common-mode filter designed for the gigahertz high-speed signals with the largest fractional bandwidth and most compact size on a PCB.

Common-Mode DC-Bus Filter Design for Variable-Speed Drive System via Transfer Ratio Measurements

Filters used in electromagnetic interference suppression are often described in literature on drive systems and have become a standard solution in industry. The effect of the commercial off-the-shelf filter depends significantly on how it is installed. A model that includes the installation parameters is made first and then the parameters of the model are extracted by transfer ratio measurements. One possibility is to include the filter on the dc-bus inside the converter. The differential mode DC-bus filter is well known, but the common-mode DC-bus filter has received little attention. Our model is used to show that the common-mode DC-bus filter can achieve the same or even better suppression of common-mode noise by careful design. The transfer ratio is used to evaluate the performance of filter design.

Analog-Based Detection Method in Optical Low-Coherence Reflectometer for Measurement of Retardation and Fast-Axis Angle

This study presents a novel detection method in optical low-coherence reflectometer for the simultaneous measurement of the reflectivity and birefringence characteristics of a sample. By implementing analog electronics in a standard two-channel time domain low-coherence reflectometer, the ratio of the envelope amplitude between two orthogonal interferometric signals, which is used for calculating the retardation angle, can then be analog-decoded using a differential detection scheme based on the quotient rule of a logarithmic function. The proposed method for direct retardation measurement benefits from common-mode noise suppression advantages that support efforts to improve the accuracy of phase retardation measurement. Furthermore, a full interferometric signal to extract the phase information is not needed for calculating fast-axis angle. Reductions in data acquisition rates and processing time are expected. The results from a calibrated test plate were correspondingly presented.