Miniature and tunable millimeter-wave lowpass filter with MEMS switch

In this paper, fully monolithic tunable millimeter-wave filters with tapped-line feedings are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass filters were designed, fabricated, and tested. The cascaded CPW-based periodic structures, with low-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 19 to 11 GHz with very small change in the average insertion loss from 1.3 to 1.9 dB. The chip size of the low-pass is 4.0 mm × 1.6 mm.     

Bulk-tuned Gm–C filter using current cancellation

A new approach for small transconductance (Gm) OTA designs, suitable for relatively low frequency filtering applications in the range of few kHz, is proposed. Small Gm values are achieved by a current cancellation technique, and are adjustable by bulk driving the MOS transistors of the input differential amplifier. The OTA design procedure takes into account Pelgrom׳s modeling of mismatch errors. A common-mode feedback control circuit based on floating gate common-mode voltage detector that shares the filter main capacitances is also presented. Experimental results obtained with a low-pass filter with tunable cutoff frequency implemented in a 0.35 μm CMOS process to verify the effectiveness of the design procedure have shown close agreement with the theory.     

一种新型的跟踪低通滤波器

介绍了一种新型的跟踪低通滤波器的原理及实现方法.该跟踪低通滤波器用八阶椭圆型开关电容滤波器MAX293构成低通滤波电路,输入信号的频率通过单片机的测量、修正、倍频处理后输出作为MAX293的时钟控制频率,用以控制MAX293的截止频率从而实现跟踪滤波.实验证明,对于0.1 Hz～25 kHz的信号,跟踪低通滤波器的截止频率相对误差小于1%.     

Real-Time Numerical Filtering of Physiological Signals

The minimization of the sampling rate necessary to store a signal frequently requires filtering of unwanted higher frequency components in order to avoid aliasing errors. In many physiological situations the desired cutoff frequency is too low to be realized by a practical passive analog filter. In such a case either an active analog filter may be used, or the signal may be initially sampled at a higher rate to avoid aliasing, then numerically filtered in real-time, and the resulting smoothed signal sampled at a lower rate (the effective sampling frequency). The purpose of this communication is to describe the use of a class of low-pass digital filters which we have found useful for this purpose.     

一种模拟滤波电路数字化方法

在信号处理中,滤波的优劣直接影响信息的准确性。模拟滤波虽然快捷但不灵活,数字滤波效果虽好但复杂。所以文中提出一种以模拟滤波器为基准,设计具有相同功能而且参数可调的数字滤波器的方法。并以二阶RC无源低通滤波电路为例对此过程进行说明,与模拟滤波电路和传统的数字滤波相比,该方法不仅比传统的数字滤波算法简单快捷,而且可有效防止模拟电路中器件的寄生参数、精度、温度等的影响,使滤波更加稳定。     

A transistor-only low-pass filter with adjustable bias and smallphase shift at high frequencies

A third-order, low-pass, transistor-only filter with a small phase shift at high frequency and an adjustable cutoff frequency is presented. This low-pass filter overcomes the structure limit of the filter previously reported and achieves the same frequency response. It has an adjustable bias voltage which makes it possible to change its cutoff frequency     

Improved narrowband low-pass IIR filters in fixed-point systems [DSP Tips & Tricks]

Due to their resistance to quantized-coefficient errors, traditional second-order infinite impulse response (IIR) filters are the fundamental building blocks in computationally efficient high-order IIR digital filter implementations. However, when used in fixed-point number systems, the inherent properties of quantized-coefficient second-order IIR filters do not readily permit their use in narrowband low-pass filtering applications. Narrowband lowpass IIR filters have traditionally had a bad reputation; for example, MATLAB's Signal Processing Toolbox documentation warns: "All classical IIR low-pass filters are ill conditioned for extremely low cutoff frequencies."     

Log-domain high-order low-pass and band-pass filters

Continuous time current-mode high-order low-pass and band-pass filters based on the log-domain concept are presented in this paper. The passive RLC ladder networks are used as the prototype to achieve the proposed filter by simulating the RLC network synthesis method. The achieved filters have inherited the good sensitivity performance from the RLC passive prototype. Fifth-order RLC ladder low-pass filter and sixth-order RLC ladder band-pass filter are used as prototypes and the signal flow graph (SFG) technique is used for the synthesis. The SFG can identify group of integrators and several signal paths. Log-domain lossy and lossless integrators based on BJT technology are deployed to achieve the integrators for realization of proposed filters. The simulations were carried out and the results exhibited several features which are in agreement with the RLC prototype. The frequency response of filters along 100 kHz to 10 MHz can be electronically tuned through 5–500 µA of bias currents. The THD lower than 1% of LP and BP filters were measured at 10 MHz input. The multi-tone tested was included in the paper for verifying the performance of proposed LP and BP filters. The intermodulation distortions around −50 dB and −60 dB were also investigated for the proposed LP and BP filters.     

On The Optimization of Fractional Order Low-Pass Filters

This paper presents three different optimization cases for normalized fractional order low-pass filters (LPFs) with numerical, circuit and experimental results. A multi-objective optimization technique is used for controlling some filter specifications, which are the transition bandwidth, the stop band frequency gain and the maximum allowable peak in the filter pass band. The extra degree of freedom provided by the fractional order parameter allows the full manipulation of the filter specifications to obtain the desired response required by any application. The proposed mathematical model is further applied to a case study of a practical second- generation current conveyor (CCII)-based fractional low-pass filter. Circuit simulations are performed for two different fractional order filters, with orders 1.6 and 3.6, with cutoff frequencies 200 and 500 Hz, respectively. Experimental results are also presented for LPF of 4.46 kHz cutoff frequency using a fabricated fractional capacitor of order 0.8, proving the validity of the proposed design approach.     

光纤激光器相干合成系统中组束误差对远场光场的影响

对光纤激光器相干合成系统中组束误差对远场光场分布的影响进行了数值研究,分析了输出单元占空比、位置误差和平行度误差对远场光场分布的影响。结果表明,输出单元占空比的增加只能提高中心光斑的能量,但无法改变中心光斑的平均光强;而位置误差会使远场光场中的旁瓣能量减弱,降低光纤激光器相干合成系统的转换效率。分析发现,位置误差的这种影响可以通过增加输出单元的占空比来减弱。最后,通过分析平行度误差对远场光场的影响,对光纤激光器相干合成系统中的平行度误差控制提出了建议。     

A low-transconductance OTA with improved linearity suitable for low-frequency Gm-C filters

A fully differential operational transconductance amplifier is presented in this paper with enhanced linearity and low transconductance, suitable for low-frequency Gm-C filters. This paper also proposes a new common-mode feedback scheme that presents low sensitivity to large differential voltage swings at the OTA outputs. The proposed OTA was employed in the design of a fully-integrated Gm-C low-pass filter with a cutoff frequency of 30 kHz. The Gm-C filter was fabricated in a 0.35 μm CMOS technology and presented a THD at the output less than 1% for input signals with differential amplitudes up to 3.2 V.     

Power and area efficient MOSFET-C filter for very low frequency applications

New circuit design techniques for implementing very high-valued resistors are presented, significantly improving power and area efficiency of analog front-end signal processing in ultra-low power biomedical systems. Ranging in value from few hundreds of M\Upomega\hbox{M}\Upomega to few hundreds of G\Upomega\hbox{G}\Upomega, the proposed floating resistors occupy a very small area, and produce accurately tunable characteristics. Using this approach, a low-pass MOSFET-C filter with tunable cutoff frequency (f _C  = 20 Hz–184 kHz) has been implemented in a conventional 0.18 μm CMOS technology. Occupying 0.045 mm²/pole, the power consumption of this filter is 540 pW/Hz/pole with a measured IMFDR of 70 dB.     

Real-time digital median frequency estimator for surfacemyoelectric signals

A prototype instrument is described that uses a digital signal processor to estimate the median frequency of the myoelectric signal in real time. A set of tenth-order digital low-pass filters is used to track the median frequency. An estimate of frequency is obtained once every 256 ms with a resolution of 1 Hz.     

简易程控声波滤波器的设计与实现

设计了一个能对10Hz～60kHz的声波信号进行精确程控滤波器系统,该系统采用STM32F103单片机作为控制核心,使用精密运放NE5532构成电压跟随缓冲部分,提高了系统滤波的精确性。程控滤波器采用CMOS双二阶通用开关电容有源滤波器MAX262构成,可通过微处理器STM32F103精确控制滤波器的传递函数（包括设置中心频率、品质因数和工作方式）,在不需外部元件的情况下就可以构成各种带通、低通以及高通滤波器;整个系统采用HD7279键盘输入以及12864LCD液晶显示,实现对滤波器的精确调节和显示设定参数。系统性能指标精度比较高,工作可靠,人机交互以及用户界面非常友好。     

A high performance Σ-Δ readout circuitry for μg resolution microaccelerometers

This paper reports a second order electromechanical sigma-delta readout for micro-g resolution accelerometers in addition to other high-sensitivity capacitive microsensors with large base capacitance. The chip implements a switched-capacitor readout front-end and an oversampled sigma-delta modulator, and hence can be used for both open-loop analog readout and closed-loop control and readout with direct digital output. The readout circuit has more than 115 dB dynamic range and can resolve less than 3 aF/√Hz. Also this IC includes start-up circuit and feedback mechanism for closed-loop control of the accelerometer with a single 5 V supply in a ±4 g range. Together with the accelerometer, bandwidth of the overall system is limited with the sensor resonance frequency (1.53 kHz) in the open-loop mode. However in closed loop mode, oversampling of the acceleration data increases the bandwidth of the system up to few hundred kilohertz which is limited with the cut-off frequency of the low-pass filter placed at the output of the system. The start-up circuit allows rebalancing of a thick silicon proof mass with the limited 5 V supply after system start from power down or in the case of over-range input acceleration. The readout chip has been combined with a Silicon-On-Glass lateral accelerometer, which has a high sensitivity of 1.88 pF/g with large proof mass and long finger structures. A digital filtration and decimation circuitry is also implemented to signal process the output bit stream of the readout circuit. The complete module consumes 16 mW from a ±2.5 V supply and has an adjustable sensitivity up to 8 V/g with a noise level of 4.8 μg/√Hz in open-loop.     

MOSFET-C filter, with low excess noise and accurate automatictuning

Continuous-time integrated filters having a maximum dynamic range at the audio-frequency range are obtained using MOSFET-C filters. Using MOSFET-C filters in combination with a well-designed BiCMOS amplifier, the detrimental influence of 1/f noise can practically be eliminated and the filter noise is completely determined by the unavoidable thermal noise of the filter resistors. A 98-dB dynamic range (total harmonic distortion<0.3%) is obtained in a fifth-order Butterworth low-pass filter, while the overall 1/f noise corner frequency is limited to 250 Hz. Automatic adjustment of the filter cutoff frequency is performed using a novel all-silicon automatic tuning system that, compared with traditional automatic tuning systems, has reduced overhead circuitry     

Compact sub-hertz OTA-C filter design with interface-trap charge pump

Single-ended and differential operational transconductance amplifier (OTA) configurations are biased with MOSFET interface-trap charge-pumping (ITCP) current generators to achieve very low transconductances for tunable sub-hertz operational transconductance amplifier-capacitor (OTA-C) filter implementation. This paper reviews the basics of ITCP current generation and presents the transconductors and the OTA-C filter configurations based on these transconductors. One of the filters is a low-pass with an experimentally determined lowest cutoff frequency of 0.18 Hz, and the other is a fully differential bandpass with individually tunable lower and upper cutoff frequencies measured down to 0.3 Hz. The former has one 15-pF filter capacitor, and measures 0.0346 mm/sup 2/, whereas the latter contains four such capacitors and occupies 0.188 mm/sup 2/ silicon. Experimental evaluation also includes offset, harmonic distortion, and noise performance.     

差分式CMOS多功能电流模式滤波器

本文提出多端输出的CMOS电流加法器，在此基础上提出了新型差分式CMOS多功能电流模式滤波器的信号流图和电路。该滤波电路能同时产生二阶低通、带通、高通输出，并通过适当的连接能产生二阶带阻和全通滤波输出。对提出的滤波器截止频率为1MHz的电路进行了计算机PSPICE仿真。     

A 3-V continuous-time filter with on-chip tuning for IS-95

This paper describes a low-voltage channel selection analog front end with continuous-time low-pass filters and on-chip tuning for a receiver in an IS-95 cellular phone. The filters were realized as balanced seventh-order elliptical g_mC filters to achieve low current consumption. The transconductors were realized by using second-generation current conveyors (CCII) and resistors to achieve good intermodulation distortion performance. A novel CCII circuit topology was developed to fulfil the low supply-voltage requirement. The cutoff frequency tuning was implemented with capacitance matrices and a time-domain master-slave tuning circuit     

A <Emphasis Type="Italic">G</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript><Emphasis Type="Italic">-C</Emphasis> continuous-time analog filter for IEEE 802.11 a/b/g/n wireless LANs

A CMOS transconductor for multi-mode wireless channel selection filter is presented. The linear transconductor is designed based on the flipped-voltage follower (FVF) circuit and an active resistor to achieve the transconductance tuning. The transconductance tuning can be obtained by changing the bias current of the active resistor. A third-order Butterworth low-pass filter implemented with the transconductors was designed by TSMC 0.18-μm CMOS process. The results show that the filter can operate with the cutoff frequency of 10–20 MHz. The tuning range would be suitable for the specifications of IEEE 802.11 a/b/g/n Wireless LANs under the consideration of saving chip areas. In the design, the maximum power consumption is 13 mW with the cutoff frequency of 20 MHz under a 1.8 V supply voltage.