Current-mode background suppression for 2-D LWIR applications

A new readout circuit involving two-step current-mode background suppression is studied for two-dimensional long wavelength infrared (2D LWIR) focal plane arrays. The simple pixel circuit has a very small skimming error of less than 0.3%, low noise characteristics for an adequate calibration range, and a long integration time of 2 ms.     

Time-based pixel-level ADC with wide dynamic range for 2-D LWIR applications

A readout circuit involving a time-based pixel-level ADC is studied for two-dimensional long wavelength infrared focal plane arrays (2-D LWIR FPAs). The integration time of each pixel can be optimised individually and automatically. Using a time-based pixel-level ADC with two-step background suppression, the signal-to-noise ratio and dynamic range can be improved to 88.8 and 95.1 dB, respectively.     

A new 2-D model for operating point shift in large LWIR HgCdTeFPA's

Infrared focal plane arrays (IRFPAs) are rapidly increasing in size. It is shown here that for large FPAs a considerable shift in the operating point occurs, which, if not reduced, introduces unacceptably large nonuniformity in the array response. This shift results because of the variable voltage drop across the HgCdTe active layer, due to its finite distributed resistance. A new analytical two-dimensional (2-D) model to estimate the operating point shift of individual detectors of long wavelength infrared (LWIR) HgCdTe focal plane array (FPA) is presented. Avoiding this operating point shift requires an optimized grid pattern     

Compact current-mode loop filter for PLL applications

A novel capacitance scaling technique is proposed to reduce on-chip capacitor area using a dual-path self-biased current-mode filter. The capacitor multiplier is obtained by the relative ratio of charge-pump currents I/sub cp2//(I/sub cp2/-I/sub cp1/), rather than the scaling ratio I/sub cp2//I/sub cp1/. Compared with the original current-mode filter, the demonstrated loop filter of 250 pF capacitance is achieved with only 25 pF (90% die area saving), and the resistor area is reduced by 50% owing to reuse of the degenerated resistor R/sub G/.     

A current-mode power sigma-delta modulator for audio applications

Linear and switching techniques are currently adopted to implement current-mode power stages. Pulsewidth modulation (PWM) is usually employed with the switching technique for both industrial and audio applications. In this paper, the Sigma-Delta modulation is considered as an alternative to the PWM in devising a switching current-mode power stage suitable for audio amplification. The proposed modulator is analyzed and simulated. The whole system was realized on an experimental breadboard. The results carried out on the prototype are reported and discussed. The electrical characterization presents interesting features in terms of linearity, noise, and power efficiency.     

CMOS current-mode divider and its applications

Compact, accurate and low-power analog CMOS circuits for current-mode division and pseudo-exponential function generation are presented, based on a new variable transresistance amplifier. Experimental results of the circuits fabricated in a 0.5-/spl mu/m 2P2M n-well CMOS process show better than 0.3% total harmonic distortion. Measured power is less than 0.22 mW at 100-MHz bandwidth and /spl plusmn/1.5-V supply voltages.     

Novel high-precision current-mode multiplier/divider

In this paper, a method to reduce the second order effects on the circuit performances caused by the small sized MOS transistors is proposed. A current mode square-root circuit, a squarer/divider circuit and a multiplier/divider circuit are designed using this method. Proposed circuits have been simulated with SPICE simulator using 0.35 μm CMOS technology parameters. The main advantages of the proposed circuit are reduced errors of the output current function, a smaller area on the chip, possibility of controlling the output current with the control voltage, operation at higher frequencies and more efficient power consumption. As a result, it can be considered as a useful building block for IC designer.     

Output stage for current-mode feedback amplifiers,theory and applications

A novel building block is described, termed FCS (floating current source), which may serve as class A output stage for CFAs (current-mode feedback amplifiers). It is capable of driving a grounded load with a bipolar signal, and yields a feedback current equal to the output current over a wide frequency range. Its possible range of application covers MOSFET amplifiers employed in analog signal processing and current-operated control systems. An internal interconnection converts the FCS into a CCII-. Another novel CCII- configuration employs a push-pull folded cascode and may serve as noninverting input stage for a standard amplifier configuration. Finally, a feedback-stabilized CCII- and a CFA are described, both employing the FCS as output stage.     

一种新的PDF417二维条形码识别算法

采用新的算法在对PDF417二维码进行解码时,将二维条码的单元模块宽度的求取和二维码码字的提取分割开来进行,很好地改进了传统的基于条码边缘图像的识别算法中由于各种原因出现的边缘检测不全、伪边缘干扰和边缘噪声污染所引起的码字丢失、错码、误码等问题.在同等条件下,可以比较精确地提取出图像码字.给出了实验结果.     

CAS-CAS transform for 2-D signals: A few applications

A few applications of a separable Hartley-like (CAS-CAS) transform in two-dimensional (2-D) signal processing is presented. The applications discussed include (i) the interpolation of signals, (ii) the computation of Hilbert transform, and (iii) the complex cepstrum computation. The computational advantage of the proposed methods over the algorithms using 2-D FFT are discussed.     

一种新颖的电流模式双二阶OTA-C滤波器设计

提出了一种新颖OTA-C实现的电流模式双二阶通用滤波器。该滤波器具有三个输入端和一个输出端,通过选择不同的输入信号即能实现低通、高通、带通、带阻和全通五种滤波器功能。电路结构简单、中心频率和品质因数可调,灵敏度低,均为0.5。理论分析和SPICE仿真表明所提电路方案正确可行。     

Response of realistic soil for GPR applications with 2-D FDTD

The three-dimensional (3D), wideband, bistatic ground penetrating radar (GPR) scatter response of rough, realistic ground is efficiently and accurately simulated using a hybrid high resolution 3D and large area two-dimensional (2D) finite difference time domain (FDTD) model. The 3D computation carefully models the transmitting and receiving antennas, while the 2D FDTD models wave propagation between the antennas and the scattering by the soil below them. The FDTD soil model considers realistic frequency dependent (dispersive) soil with Gaussian height variations. The modeling results are compared to experiments performed with the Geo-Centers, Inc., Newton, MA, commercially available GPR system used for mine detection. Despite the simplicity of the 2D model, the results of the simulation and the experiment agree quite well     

海空背景长波红外大气透过率的仿真计算方法

红外光波波段海空背景大气透过率的仿真计算在原有理论计算的基础上,修正了海背景中大气饱和水汽压的计算,推出了沉积水量的表达式,考虑了不同高度分子吸收问题,分别拟合出了在海平面水平路程上由波长和沉积水层厚度决定的水汽光谱透过率函数以及由波长和路程长决定的二氧化碳光谱透过率函数,分析了臭氧的影响,给出了大气透过率的表达式。     

Novel current-mode active-only biquad with loss-less and lossy integrators

This paper presents a realization of a current-mode active-only biquad with a two-integrator loop structure. The proposed circuit is constructed solely with operational amplifiers (OAs) and operational transconductance amplifiers (OTAs). The circuit can realize low-pass, band-pass, high-pass, band-stop and all-pass transfer functions, and the circuit characteristics can be electronically tuned by adjusting the transconductance gains of the OTAs. An example is given together with simulated results by PSPICE. The circuit configuration is very suitable for implementation in both bipolar and CMOS technologies.     

Novel slot antennas for harmonic suppression

In this paper, novel microstrip-fed slot antennas with simple structure are proposed to achieve suppression of harmonics. To obtain this operation, conductor lines connected with ground plane in rectangular and meander type slot antennas are used, which have wide-bandstop characteristic. From the measured input impedances and radiation patterns of the proposed antennas, the second and third harmonics are effectively suppressed.     

The design of low voltage/power current-mode sinh-domain filter for biomedical applications

This paper proposes low voltage/power, current-mode second-order Butterworth high-pass filter design in the sinh-domain for biomedical applications. The proposed filter is a continuous-time filter in the companding-class. Sinh-domain filters have the advantages of electronically adjusting the frequency response without the need for non-chip capacitors and full integration on the chip, providing low power consumption and offering a high dynamic range. These advantages of the sinh-domain are beneficial for biomedical applications due to its low power consumption requirement. The proposed filter topology is suitable for eliminating low-frequency interferences of biomedical signals like electrocardiogram (ECG), electroencephalogram (EEG), and electromyogram (EMG). In the realization of this filter, the method of simulation of passive elements with sinh-domain cells is used. The proposed high-pass filter in the 0.05 Hz-20 Hz operating frequency range with a 0.5 V power supply shows the power dissipation of 12.5 nW while its dynamic range exceeds 60 dB. Additionally, no resistances are used in the proposed topology. Simulations have been performed by using OrCAD Capture CIS to demonstrate the performance of the filter. These simulations have been implemented with the TSMC 0.25 µm CMOS process parameters.

     

Design of concurrent error detectable current-mode A/D converters for real-time applications

Analog MOS circuits are becoming increasingly sophisticated in terms of checking and correcting themselves. Self-correcting, self-compensating, or self-calibrating techniques eliminate errors traditionally associated with analog circuits. For real-time applications, however, it is rather difficult to achieve validation of the data generated from analog-to-digital (A/D) converters in the presence of faulty switching element(s). Conventionally, the validation is accomplished by using a high resolution and high accuracy D/A converter and a window comparator; i.e., the validation must highly depend on the reliability of both the D/A converter and the window comparator. In this paper, a novel current-mode A/D converter design with concurrent error detection (CED) capability is presented. The A/D converter does not need well-matched components and high-gain amplifiers. Results show that the proposed design can detect all the transient faults and most of the permanent faults. The proposed design allows users to easily switch to the normal operation mode where CED capability is not used, without causing any performance degradation.     

2-D symmetry: theory and filter design applications

In this comprehensive review article, we present the theory of symmetry in two-dimensional (2-D) filter functions and in 2-D Fourier transforms. It is shown that when a filter frequency response possesses symmetry, the realization problem becomes relatively simple. Further, when the frequency response has no symmetry, there is a technique to decompose that frequency response into components each of which has the desired symmetry. This again reduces the complexity of two-dimensional filter design. A number of filter design examples are illustrated.     

二维RAKE接收机中一种新的信道矢量估计算法

在二维RAKE接收机中，通常仅用导频信道来估计信道矢量，当导频功率较低时，估计误差较大。本文提出一种新的信道矢量估计算法，该算法采用导频信道与业务信道联合估计技术，通过分集组合两个信道的估计结果，使信道矢量的估计精度得到了提高，仿真结果表明，该算法能有效地降低系统的误码率。     

Novel GaAs/AlGaAs multiquantum-well Schottky-junction device andits photovoltaic LWIR detection

The authors have demonstrated photovoltaic detection for a multiple-quantum-well (MQW) long-wavelength infrared (LWIR) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5×10^-14 A for a 100×100 μm² detector (designed for 10-μm response) at 40 K, nearly nine orders of magnitude lower than that of a similar MQW LWIR detector without the blocking layer. The ideality factor is ~1.01-1.05 at T=40-80 K. The measured Schottky-barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also report a measured effective Richardson constant (A**) for a GaAs/AlGaAs heterojunction using this blocking layer structure. The A** is ~2.3 A/cm²/K ²