A broadband terahertz quarter wave plate based on asymmetric cross slots

In this paper, a transmissive terahertz (THz) quarter wave plate (QWP) has been proposed to realize the linear-to-circular polarization conversion in terahertz range. This quarter wave plate is composed of two dielectric layers and one metallic layer with asymmetric cross slots. In the range of 0.894—1.378 THz, the axis ratio of proposed device is less than 3 dB, and its polarization conversion efficiency is more than 45%. The distributions of surface currents and electromagnetic field density had been proposed to understand the physical mechanism of proposed device. The linear-to-circular polarization conversion can be attributed to the asymmetric transmission along slots. Finally, the simulation results are validated by experiments in terahertz region. The proposed device has simple geometry and good performance, which can be used as a key component in applications of terahertz communications, terahertz imaging and terahertz sensing.     

Transmission Characteristics of Sagnac Loop with Fiber Bragg Grating

A transmission filter composed of a Sagnac loop and a fiber Bragg grating is studied in detail.It is found that the transmission spectrum of this filter is the splitting of the reflection spectrum of the fiber Bragg gratings.The filter can behave as a multiple-passband filter when the fiber Bragg grating is strong and as a single-band filter when the fiber Bragg grating is weak.Very narrow transmission filters can be obtained in this way.     

A novel dual-beam terahertz leaky-wave antenna based on spoof surface plasmon waveguide

A novel dual-beam terahertz (THz) leaky-wave antenna (LWA) based on triple-periodically (TP) modulated spoof surface plasmon (SSP) waveguide is proposed. It is shown that SSP can be effectively excited and propagated along the surface of parallel corrugated metallic strips. Through proper design, the n=?1 and n=?2 Floquet modes are brought into the leakage radiation region simultaneously. Consequently, the forward and backward propagating waves corresponding to the two modes respectively generate two radiation beams in the far-field region. The proposed antenna is capable of steering the forward beam within a range of 34° and the backward beam within a range of 48° when frequency is swept between 0.23 THz and 0.29 THz. A simulated peak gain of 11.4 dBi and gain variation of 2.87 dBi are achieved within the band. The proposed LWA can be applied in THz wireless communication and radar systems.     

Instantaneous microwave frequency measurement based on hybrid microwave photonic filter

A novel photonic technique for instantaneous microwave frequency measurement based on hybrid microwave photonic filter （HMPF） is proposed and experimentally demonstrated. The HMPF is composed of an all-pass filter and a band-pass filter with negative coefficients. By properly controlling the power relationship between the all-pass filter and the band-pass filter, the HMPF can realize a monotonic frequency response, and then a unique relationship be- tween the output power and the input frequency is established. A high measurement resolution can be achieved for a given frequency range.     

A NEW MULTIFUNCTION SWITCHED-CURRENT FILTER

A new switched-current(SI)biquadratic filter is presented which can simultaneouslyprovide the low-pass,high-pass and band-pass filters in a single building block.A symbol torepresent the universal SI integrator is also introduced.It can simplify the analysis and synthesisof SI networks.     

Attenuation of terahertz transmission through rain

Based on the Marshall-Palmer,Weibull raindrop size distribution and Mie electromagnetic scattering model,the relationships of attenuation coefficient of terahertz(THz) atmospheric window waves with precipitation rate and temperature are studied.Furthermore,combined with the loss of electromagnetic wave transmission in free space,the attenuation of THz communication and the transmission of current mobile communication signals through rain are compared and analyzed.The results show that the attenuation coefficient of THz transmission is increased with increasing precipitation rate,the difference of attenuation coefficient at different THz window waves is small,and the maximum difference is about 3 dB.The rain attenuation of THz wave is first decreased and then increased with increasing temperature,but the temperature has little effect on it.The attenuation of THz wave through rain is much larger than that of mobile communication signal.     

Design and experimental study of compensation fitting on the angle-tuned filters

For a 100 GHz DWDM angle-tuned filter with low polarization dependent loss, the insertion loss and the Gaussian- transformation tendency of the transmission spectrum will become more serious as the incident angle is increased. It is because of that the optical path and the transmission modes of the thin film filter will change when the incident angle is varied. According to the thin film matrix theory, the analysis model is established, the displacement change of the transmis- sion field is simulated, and a dynamic compensation fitting is also designed and fabricated in the paper. The experimental results show that it can effectively reduce the insertion loss and the phenomenon of Gaussian process. Using the compen- sation fitting, the tunable range of the filter is at about 20 nm which coincides with the theoretical design.     

Terahertz radiation of a butterfly-shaped photoconductive antenna (invited)

The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna (PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup. To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation, polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material, radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.     

Design and implementation of a low-pass filter for microsensor signal processing

A novel low-pass filter that consists of a switched capacitor filter(SCF) and its antialiasing prefilter and smoothing postfilter is proposed for a microsensor signal processing system,which is used in separation point detection on the surface of micro air vehicles.In the system,the filter is not only applied to finish the function of filtering but also used as the front end antialiasing filter of the over sampling analog-to-digital converter.This proposed implementation mostly relies on the design of a ...     

First-principles study on transport properties of zigzag graphene nanoribbon with different spin-configurations

The current-voltage(I-V) characteristics and the transmission spectra of zigzag graphene nanoribbon with different spin-configurations are investigated by using first-principles calculations.It is shown that the I-V curves and transmission spectra strongly depend on the spin-configurations of the two sides of the ribbon.For the spin-parallel configuration structure,the curve is linear under lower bias voltage;for the spin-antiparallel configuration structure,there is a strong spin-polarization-dependent transmission which implies that the ribbon can be used as a spin filter;while for other spin-configuration structures,the curve has the characteristics of a semiconductor. It is found that there is a large magneto-resistance(MR) when the bias voltage is small.The impurity in the central scattering region significantly influences the spin-dependent current and the spin filter efficiency,which may lead the large MR to disappear.     

Transmission Line Model Based CAD of Multilayer Dielectric Filters

A systematical procedure for multilayer dielectric filter design is introduced here based on the transmission line model (TLMBCAD). By this procedure, low-pass, high-pass, and band-pass filters can be designed in the same way. The transmission line model works well and is time efficient not only for normal incidence of linearly polarized wave but also for oblique incidence wave with circular polarization. Design examples are given for low-pass and band-pass filters. Simulation results show that the method developed in this paper is valuable for the engineering design of multilayer dielectric filters.     

Design and analysis of MISO bi-quad active filter

ABSTRACT

In this paper, a multiple-input single-output (MISO) voltage-mode bi-quad active filter using voltage differencing voltage transconductance amplifier (VDVTA) is designed and analysed. The filter can realize several functions such as low-pass (LP), high-pass (HP), band-pass (BP), band-reject (BR) and all-pass (AP). The proposed configuration employs three input voltages and generates a single output voltage. The filter characteristics, i.e., pole frequency (ω_p) and quality factor (Q) are electronically tunable through the bias current of the VDVTA. The filter performance is analysed through sensitivity analysis in presence of parasitics as well as process, voltage and temperature fluctuations. The proposed design is implemented in a 45-nm CMOS technology and simulated using Virtuoso Analog Design Environment of Cadence.     

ICCII-based universal current-mode analog filter employing only grounded passive components

In this paper, three versions of a novel second-order current-mode (CM) single-input three-output analog filter employing inverting second-generation current conveyors (ICCIIs) and only grounded passive components, are presented. This filter can simultaneously realize low-pass, band-pass and high-pass responses, and can also realize notch and all-pass filter responses with interconnection of the relevant output currents. The presented second-order filter requires no active and passive element matching conditions and/or cancellation constraints. The proposed filter offers orthogonal control of angular resonance frequency (ω_o) and quality factor (Q). The proposed filter can realize filter responses at high output impedances, and has low active and passive component sensitivities. Additionally, three versions of a high-order filter derived from the proposed filter are introduced. Simulation results using SPICE program are given to show the performance of the filter and verify the theory. Signal limitations and non-ideal current and voltage gain effects of the proposed second-order filter are also investigated.     

Voltage mode universal filters employing single FDCCII

In this paper, four new voltage-mode universal biquad filters configuration are proposed. First of two circuits proposed high-input impedance universal filter with single-input and three-outputs, which can simultaneously realize voltage mode low-pass, band-pass and high-pass filter responses employing all grounded passive components. The third proposed universal filter three-input and single-output, which also can realize all the standard filter functions. The fourth circuit proposed universal filter with three-input and five-outputs, which can be used as either a three-inputs single-output or a two-inputs five-outputs universal filters. It can realize all five different generic filtering signals: low-pass, band-pass, high-pass, band-stop and all-pass. Simulation results are given to confirm the theoretical analysis. The proposed biquad filters are simulated using TSMC CMOS 0.35 μm technology.     

基于第三代电流传输器的有源滤波器的导出

阐述了由电压模式有源RC滤波器导出基于电流传输器(CCIII)的电流模式连续时间滤波器的方法.即由运算放大器(OA)滤波器导出CC滤波器;导出的电流模式2阶滤波器结构简单,能实现2阶低通、高通、带通滤波,不仅所有无源和有源灵敏度都很低,而且当无源参数确定后,有源参数对极点频率W0不产生影响,W0保持恒定.HSPICE仿真表明,提出的电路是可行的.     

Realization of Tunable Pole-Q Current-Mode OTA-C Universal Filter

A realization of a current-mode operational transconductance amplifier-capacitor (OTA-C) universal filter with tunable pole-Q is proposed. A biquadratic band-reject function is used as the initial synthesis function based on three integrator blocks. Consequently, the proposed filter uses a total of three multiple-output OTAs and three grounded capacitors. Five types of transfer functions, namely, low-pass, high-pass, band-pass, band-reject, and all-pass responses, can be obtained without changing the circuit topology. The pole-Q (Q ₀) and the pole-frequency (ω ₀) parameters are independently tuned. The Q ₀ and ω ₀ parameters are electronically tuned by adjusting the transconductance gains of the OTAs. Furthermore, Q ₀ can be tuned by varying the capacitor manually without affecting ω ₀. SPICE simulation results of the proposed filter are presented.     

多孔硅薄膜对p 型单晶硅太赫兹波段透射特性的影响

利用化学腐蚀方法,在低阻值p型单晶硅片上制备了火山口形、准纳米孔柱形和多孔形三种形貌的多孔硅薄膜。以空气为参考基准,0.2～10 THz时域光谱显示,火山口形样品在0.2～6 THz的透射强度下降了约1/2,另外两种样品强度下降了约1/5。火山口形、准纳米孔柱形样品呈现低通滤波特性,多孔形样品呈现级联带通特性。准纳米孔柱形样品截止频率比火山口形样品和多孔形样品提高了3 THz左右。样品的频谱出现多处吸收峰,峰的位置与薄膜的几何结构尺寸有关。实验结果表明:多孔薄膜的形状和几何结构尺寸改变了p型单晶硅的太赫兹波段透射强度、吸收频率和截止,该材料可以成为从太赫兹波段至可见光波段的宽频段探测材料和调制材料。     

基于AOA电流模式KHN滤波器的设计

根据伴随网络的概念,以基于VFA(电压反馈放大器)电压模式KHN(Kerwin,Huelsman,Newcomb)滤波器为原型,给出了AOA(伴随运算放大器)电流模式KHN滤波器。通过改变输入信号的作用点,该电路可分别实现高通、带通和低通输出。该电路不仅具有速度高、频带宽、电压低及功耗小等电流模式电路的特点,而且其极点角频率与品质因素独立可调,低的无源灵敏度,电路简单,适合VLSI单片集成技术。     

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.     

Tunable mixed-mode OTA-C universal filter

A novel electronically tunable mixed-mode universal biquad by using four single-output and one dual-output-operational transconductance amplifiers, two grounded capacitors is proposed. The proposed circuit has ability to realize voltage, current, transconductance, and transresistance mode, and can the following advantageous features: (i) realization of low-pass, band-pass, high-pass, notch, and all-pass filter responses from the same configuration, (ii) employment of only grounded capacitors ideal for integrated circuit implementation, (iii) orthogonal controlling of ω _o and Q for easily electronic tunability, and (iv) low active and passive sensitivity performance. Finally, to verify our architecture, we have designed this analog filter chip with TSMC 0.35-μm 2P4M CMOS technology. This chip operates to 1 MHz and consumes 30.95 mW. The chip area of the analog filter is about 0.823 mm².