An Embedded Common-Mode Suppression Filter for GHz Differential Signals Using Periodic Defected Ground Plane

A novel low-cost filter design for common-mode noise suppression in high-speed differential signals is proposed. It is realized by periodically etching the dumbbell-shape defected ground structure (DGS) to perturb the return current of the common- mode noise. A transmission-line model for the proposed structure is also developed with good agreement to the full-wave simulation and measurement result. It is found that over 20 dB suppression of common-mode noise can be achieved over a wide frequency range from 3.3 to 5.7 GHz with 3 cascaded DGS cells, while the differential signals still keep good signal integrity in eye-pattern observation. The common-mode current, which generally results in common-mode EMI, on the attached input/output cable is also proved to be efficiently suppressed (15 dB in average) within the stopband by the proposed filter.     

Balanced Coupled-Resonator Bandpass Filters Using Multisection Resonators for Common-Mode Suppression and Stopband Extension

Novel fourth-order balanced coupled-resonator bandpass filters are proposed using suitably designed half-wavelength (lambda/2) multisection resonators for common-mode suppression. By properly designing the input/output (I/O) resonators associated with the filter composed of four bi-section resonators, a balanced filter with good common-mode suppression is realized, but its rejection bandwidth is rather limited. To widen the rejection bandwidth, the I/O bi-section resonators are replaced by the tri-section ones so that a balanced filter with good common-mode suppression and wide rejection bandwidth may be realized by suitably arranging the composed bi-/tri-section resonators. Specifically, a stopband-extended balanced filter with good common-mode suppression (>50 dB) within the differential-mode passband is implemented and its stopbands are also extended up to 5f₀ ^d with a rejection level of 30 dB, where f₀ ^d is the center frequency in differential-mode operation.     

Independent common-mode and differential-mode design of fully differential analog filters

Fully differential filter design is usually made departing from a single-ended prototype. This procedure guarantees the desired differential-mode response, but does not take into account common-mode dynamics, which could present nonacceptable transient responses or stability problems. A state-space design technique, which provides control of both differential and common-mode responses, is proposed. It is based on a feedback topology that allows independent assignment of differential and common-mode eigenvalues. This technique ensures circuit stability and also provides a high common-mode rejection ratio, which is independent of component unbalances. Experimental results on a first-order state-space filter are presented.     

A New Carrier-Based PWM Providing Common-Mode-Current Reduction and DC-Bus Balancing for Three-Level Inverters

Adjustable-speed drives involve common-mode voltages, which generate common-mode currents flowing to the ground through stray capacitances of electric machines. These currents are known to provoke premature motor-bearing failures, as well as electromagnetic interferences disturbing neighbor electronic devices. Furthermore, high-voltage applications involve high levels of these conducted emissions, which must be lowered by using bulky and expensive filters. This paper aims at elaborating a new pulsewidth-modulation (PWM) strategy in order to reduce the common-mode currents generated by three-level neutral-point-clamped inverters. The proposed strategy also provides the ability to balance the neutral point of the dc-bus capacitors. Experimental results both in time and frequency domains confirm that the new PWM improves the electromagnetic-compatibility behavior of the drive compared with conventional strategies.     

Design of a wideband common-mode filter using approximate closed-loop pattern of compact C-shaped defected ground structure

A compact common-mode filter is proposed to suppress common-mode noise for application of high-speed differential signal traces. The filter adopts one big C-shaped defected ground structure (DGS) cell in the left of ground plane and two small C-shaped DGS cells with opposite direction in the right of ground plane. Because these DGS cells have different dimensions, the filter has three adjacent equivalent resonant points, which can suppress wideband common-mode noise effectively. The left C-shaped DGS and its adjacent C-shaped DGS cell form an approximate closed structure, which can efficiently reduce the influence of the mutual capacitance. The filter provides a common-mode suppression from 3.6 GHz to 14.4 GHz over 15 dB while it has a small size of 10 mm10 mm. The fractional bandwidth of the filter is 120%, and the differential signals still keep good signal integrity. The experimental results are in good agreement with the simulated results.     

A Differential-Mode Wideband Bandpass Filter on Microstrip Line for UWB Application

A differential-mode wideband bandpass filter (BPF) on microstrip line is proposed with good common-mode suppression. A four port two stage branch-line differential-mode BPF is first designed. Then, open circuited stubs are attached to the middle of two of the vertical branches. As such, its two-port bisection becomes a bandpass or bandstop filtering topology under differental- or common-mode excitations, respectively. The lengths and widths of these stubs can be properly adjusted to produce a highly attenuated and widened stopband under the common-mode operation. Finally, a wideband differential-mode BPF is designed and fabricated. The predicted and measured performances are in good agreement with each other, showing good common-mode suppression with an insertion loss higher than 20 dB over the differential-mode passband with a fractional bandwidth of 65%.     

基于补偿原理的逆变器EMI抑制方法研究

由于逆变器电源对输出接地电容的限制,对严重的共模电磁干扰难以用大容量的共模滤波器抑制共模噪声。文章介绍了一种新型的基于噪声电流补偿原理的电力电子装置无源干扰抑制技术,探讨了不同方案实现对共模噪声电流的补偿,并在一台DC/AC逆变器中进行了补偿测试。实验结果证实了该EMI抑制方法的有效性。     

基于环形谐振器的平衡式带通滤波器

提出了一种基于多模环形谐振器实现的平衡式带通滤波器, 其主要由加载了电阻和短路枝节的环形谐振器和两对平衡端口构成.所提出的滤波器能够以单个谐振器获得差模的双模响应, 并且具有结构简单, 共模抑制高, 带宽可进行有限控制(4% ~ 9%)的优点.为验证理论预期的可实现性, 在RO4003C基板上设计了一个工作在1.87 GHz的平衡式带通滤波器.实验结果表明该滤波器的20-dB阻抗匹配带宽为8.9%, 中心频率处的插入损耗为0.86 dB, 在1 ~ 3 GHz频率范围内的共模抑制大于30 dB.     

Differential-mode ultra-wideband bandpass filter on microstrip line

A differential-mode ultra-wideband (UWB) bandpass filter on a microstrip line is proposed and implemented with good common-mode suppression. A sixth-stage branch-line differential-mode bandpass filter is designed with the specified UWB passband. By introducing two pairs of open-circuited stubs in the symmetrical plane, the differential-mode frequency response remains unchanged but its common-mode counterpart is reshaped to achieve the stopband in the overall UWB. A filter is then fabricated for experimental verification of the proposed technique.     

A 100-dB CMRR CMOS Operational Amplifier With Single-Supply Capability

A CMOS operational amplifier that has a common-mode rejection ratio (CMRR), a power-supply rejection ratio (PSRR), and gain above 100 dB for each of these parameters is described. This is achieved by combining a high output-impedance tail current source with a stable drain-source voltage of the input transistors. The common-mode input signal range includes the negative rail. This is obtained by controlling the bulk bias of the input and cascoding transistors. The amplifier consists of two gain stages connected via cascoded current mirrors. The gain is improved by using gain boost in the current mirrors, and by the suppression of impact ionization current in the output stage     

DC transfer characteristic, offset voltage sensitivities, and CMRR of FET differential stages

Using a simple square-law model of the field-effect transistor, the nonlinear dc transfer characteristic of FET differential stages is described for matched and unmatched input transistors. The input offset voltage sensitivities with respect to small imbalances of FET parameters and load device values are calculated for different load configurations. The common-mode rejection ratio (CMRR) is also considered.     

Suppression of common-mode beat noise from optical amplifiers using a balanced receiver

When a coherent (heterodyne or homodyne), single-mixer type optical receiver is combined with an optical preamplifier or in-line amplifier(s), the S/N is deteriorated severely due to the common-mode (signal-ASE and ASE-ASE) beat noise. When a balanced-type coherent receiver is used, the common-mode beat noise can be suppressed and the ideal, so-called LO-ASE beat-noise limited, S/N ratio is attainable. The authors present a clear experimental demonstration of the suppression of common-mode beat noise by a balanced receiver. The minimum required LO power is determined by the thermal noise or the common-mode rejection ratio (CMRR) of the balanced receiver.<>     

Novel Balanced Dual-Band Bandpass Filter Using Coupled Stepped-Impedance Resonators

A novel balanced dual-band bandpass filter, using coupled stepped-impedance resonators (SIRs), is proposed in this letter. The differential- and common-mode equivalent half circuits are given. By properly designing the resonators, associated with the filter composed of eight SIRs, dual-band differential-mode bandpass response can be obtained. To improve the common-mode suppression level, two open stubs with different lengths are added to the connection point of two resonators. A prototype balanced filter operating at 2.4 and 5 GHz has been realized to validate the proposed concept and theory.      

Coupling between differential signals and the dc power-bus in multilayer PCBs

Differential and common-mode transfer impedances are proposed herein to analyze noise coupled to (from) the dc power-bus from (to) via transitions in differential signals. Expressions for the two transfer impedances in terms of conventional single-ended transfer impedances are derived and verified through measurements, full-wave finite-difference time-domain (FDTD) simulations and an analytical cavity model. Some properties of the differential and common-mode transfer impedances are investigated to facilitate engineering design. The impact of signal current imbalances on power-bus noise and the benefit of differential signals as compared to single-ended signals are quantified.     

反激式开关稳压电源传导干扰研究

开关式直流稳压电源的电磁干扰不仅对电网产生干扰,导致在同一电网上供电的其它设备不能正常工作,而且严重的谐波电压电流会在开关电源内部产生电磁干扰,从而造成开关电源内部工作不稳定,使开关电源性能降低。文中以反激式开关稳压电源为研究对象,主要分析了传导测试中,差模、共模传导两种方式噪声源的产生机理,建立了开关电源传导干扰模型,采用EMI滤波器即共模滤波和差模滤波,并详细研究了加入π型滤波器、输入x电容、共模扼流圈等对开关稳压电源传导干扰的抑制效果,得出传导干扰抑制在标准限制范围的改进措施,整改后可让传导干扰强度从100μV降低到200 nV并通过认证。研究结果表明该措施对抑制开关稳压电源传导干扰是有效的。     

基于3×3和2×2耦合器的非对称交错滤波器的设计

为提高MZI(马赫-曾徳干涉仪)型交错滤波器的输出光平坦度,扩大信道带宽,提出了由1个3×3和两个2×2单模光纤耦合器组成的全光纤级联MZI型交错滤波器,用传输矩阵法推导出了模型的输出谱和相关参数之间的表达式并进行了特性分析。结果表明:当耦合器的分光比和光纤干涉臂之差为定值时,可以产生理想的交错谱图。这种滤波器信道间隔为2nm。此外应用双环光纤辅助的方法可使得输出波形的顶端更加平坦,边模抑制比贴近理论值。     

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 $0.16~{mmb{lambda}}{hbox{g}} times 0.26~{mmb{lambda}}{hbox{g}}$ with the corresponding real size of ${hbox{3.2}}~{hbox{mm}}times {hbox{5.12}}~{hbox{mm}}$. 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 band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter（MPF）based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated.In the experiment,a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source（BOS）with a Lyot-Sagnac filter.A standard single-mode fiber（SMF）and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio（MSSR）and Q-factor of the filter.The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator.The results have significant guidance for MPF design by choosing appropriate devices and parameters.Based on the analyses,a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of0.01,the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.     

Low-distortion switched-capacitor filter design techniques

The distortion mechanism in switched-capacitor (SC) filters are considered, and closed-form expression relating switched-capacitors filter distortion to circuit parameters are derived. Design techniques for low-distortion applications are discussed and are applied to a sixth-order experimental filter. The filter design uses a fully differential class A/B op amp with a continuous-time common-mode feedback circuit. Distortion measurements show that for 82-dB dynamic range (relative to noise floor) the total harmonic distortion of 0.02% within the whole 4-kHz bandwidth and 0.07% within 20-kHz bandwidth.     

A low-distortion BiCMOS seventh-order Bessel filter operating at2.5 V supply

This paper presents the design of a seventh-order continuous-time Bessel filter using a new low-voltage and highly linear BiCMOS transconductor. A high-gain and parasitic-insensitive integrator is obtained by using an active capacitor scheme. The filter has been designed to operate at a 2.5 V supply with a nominal -3 dB cutoff frequency of 600 kHz. It has been fabricated in 1 μm, double-poly 6-GHz BiCMOS process. The inband group delay variation is less than 10 ns. The total harmonic distortion (THD) measured with a 100 kHz input signal is less than -49 dB for a 2 V_pp amplitude and the dynamic range is 77 dB. The filter can be frequency tuned over almost one decade with a gain variation less than 0.2 dB in the passband. A common-mode rejection ratio (CMRR) of 53 dB in the passband is observed, thanks to a careful common-mode control strategy