基于硅光电倍增管的PET前端读出ASIC设计

针对SPM探测器的特点,采用TSMC 0.18μm CMOS工艺,设计了基于SPM的PET前端读出ASIC芯片,包括RGC前置放大器、积分器、整形器、采样保持电路等能量测量电路,以及鉴别器、单稳态电路等时间测量电路.Hspice仿真结果表明,该电路能够完成对SPM探测器输出信号的读出和处理功能,满足PET系统设计要求.     

用于GaN半桥驱动器的高速电平移位电路

设计了一种GaN半桥驱动器高性能电平移位电路,一方面采用短脉冲控制的高速镜像噪声电流与噪声电流相互抵消的方法消除共模噪声,另一方面采用脉冲宽度调制(PWM)控制的正反馈互锁电路,该电路不含RC滤波,用来消除由于工艺偏差造成的差模噪声,以保证输出信号稳定。抗负压电路采用降压电平移位电路实时监测高侧电压浮动状态并反馈回自举充电回路,使充电时间避开负压时间。在0.18μm 85 V BCD工艺下完成设计,工作频率达到5 MHz,上升时间为4.1 ns,下降时间为3.8 ns,满足高频GaN栅驱动应用需求。     

斜采样技术的混叠分析及分辨率计算

 斜采样技术通过将线阵探测器倾斜一定的角度并调节积分时间的方法,利用较低成本实现了探测器的亚像元成像.本文对单线阵斜采样及超模式斜采样方式的混叠及分辨率进行了研究.通过对采样方式在频域对偶网格的分析,建立了斜采样成像系统与混叠的关系,在有效分辨率的意义下,确定了混叠与噪声最小的最佳倒易晶胞,将错位的频谱恢复到了正确的位置,提高了分辨率.实验结果表明,通过最佳倒易晶胞去除混叠的斜采样技术有效地提高了线阵采样式光学遥感器图像分辨率.     

高精度3阶delta-sigma调制器的设计

本文设计了一个用在ADC(ADC)中的3阶8级量化的delta-sigma调制器(DSM)。该调制器的过采样率128,信号带宽32.8 kHz,分辨率16位。在设计噪声传输函数(NTF)时采用前馈方式实现极点和局部反馈实现零点,从而优化了输出信噪比,通过这些方法提高动态范围(DR),降低量化噪声。这个DSM的峰值信噪比可以达到145dB以上。最后本文给出了这个DSM的MATLAB仿真模型及仿真结果,在此模型基础上编写电路模块verilog程序及进行行为级建模。     

空间光通信中CCD亚像素的分辨率

在空间光通信跟踪、瞄准和捕获(APT)系统中,探测终端的位置分辨率对整个通信系统的性能起着巨大的影响,为了使终端探测器的分辨率达到系统的要求,进一步提高跟踪、瞄准和捕获系统的性能,提出了一种新的提高探测器CCD分辨率的方法,即多次采样处理。通过将两次采样的数据进行叠加处理,然后利用软件进行控制,可使CCD的位置分辨率提高到亚像素的精度。模拟结果表明,利用该多次采样处理可以将CCD的位置分辨率提高到1/2像素,1/4像素或更高的精度。同时该方法还可以抵消诸如散粒噪声、暗电流噪流起伏等噪声,从而使信噪比得到提高。     

数字CR-(RC)n滤波器的脉冲成形技术研究

为保证放射性测量系统的能量分辨率,探测器输出脉冲通常被成形为高斯或类高斯波形。本文基于CR-(RC)ⁿ电路,将CR-(RC)ⁿ电路分解为CR电路和RC电路,然后采用数值微分方法分别建立CR电路、RC电路数学模型,实现数字CR-(RC)ⁿ脉冲成形。通过模拟串行噪声和并行噪声,对比了数字CR-(RC)ⁿ脉冲成形与梯形脉冲成形的滤波效果。实验结果表明,在相同达峰时间条件下,数字CR-(RC)ⁿ脉冲成形对串行噪声、并行噪声的滤波效果较梯形脉冲成形滤波效果好;CR-(RC)⁴脉冲成形对串行噪声、并行噪声的滤波效果较n=1,2,3时好;CR-RC脉冲成形对上升时间的免疫能力较CR-(RC)²,CR-(RC)³,CR-(RC)⁴脉冲成形强。     

一种高速高可靠性低功耗的电平位移电路

为了满足MHz以上频率的GaN半桥栅驱动系统的应用需求,提出了一种高速高可靠性低功耗的低FOM电平位移电路。串联可控正反馈电平位移电路通过仅在转换过程中减弱正反馈力度,实现了低传输延迟和高共模噪声抗扰能力,同时采用最小短脉冲电路设计以降低功耗。该电平位移电路基于0.5 μm 80 V高压(HV) CMOS工艺进行设计与仿真验证,结果表明,电路具有960 ps的传输延时、50 V/ns的共模噪声抗扰能力和0.024 ns/(μm·V)的FOM值。     

极紫外光子计数成像探测器采集电路的研制

为了使极紫外光子计数成像探测器能够高速采集数据并显示光子位置信息,研制了一款数据采集电路系统。分析了基于感应电荷楔条形位置灵敏阳极光子计数成像探测器的成像原理,选用符合性能要求的模数(A/D)转换芯片,在现场可编程门阵列(FPGA)主控芯片的控制下对去除峰值保持电路模块的模拟信号进行采样和转换。FPGA将接收到的数字信号处理以后通过USB数据传输系统发送给计算机,上位机软件再进行解包、计算和成像等工作,将光子的位置图像显示出来。最后对所成图像的线性度和分辨率进行鉴定。实验结果表明,该电路系统具有最高为2 MHz的采样速度和3路同步采样能力,并且在没有峰值保持电路的情况下采集到的图像仍具有很好的线性度和高达5 lp/mm的空间分辨率。能快捷准确地完成数据采集和绘图成像,满足极紫外探测器对采集电路的性能要求。     

一种新型Ce∶GAGG闪烁探测器性能研究

该文将新型掺铈钆稼铝石榴石(Ce∶GAGG)闪烁晶体与CR 173光电倍增管耦合,并将其和分压电路、高压模块、前放电路一起封装在铝合金外壳中,制成新型Ce∶GAGG闪烁探测器。研究了不同尺寸Ce∶GAGG闪烁晶体、不同耦合方式及反射层封装材料对新型Ce∶GAGG闪烁探测器光产额和能量分辨率的影响,同时与封装好的1英寸(1英寸=2.54 cm)掺铊碘化钠(NaI(Tl))闪烁晶体进行对比实验,并对Ce∶GAGG和NaI(Tl)闪烁探测器的能量线性进行测量。实验结果表明,小体积的Ce∶GAGG闪烁探测器性能最好;光学硅脂耦合可提高闪烁探测器的性能;银反射膜（ESR膜）材料封装闪烁探测器性能最好;Ce∶GAGG闪烁探测器性能优于NaI(Tl)闪烁探测器。     

UWB脉冲信号的时域波束形成方法

分析了超宽带（Ultra Wideband）脉冲信号阵列空时处理的一般原理,比较了它和传统正弦阵列的差别,给出了一种高精度的时域波束形成方法。精确的可变时延电路实现是时域波束形成的主要问题,采用数字延迟线和FIR延迟补偿滤波器相结合的办法实现UWB信号波束形成的数字化处理。设计了因果稳定的高精度的具有分数时延补偿特性的FIR滤波器,解决了UWB信号在小样本采样时时间量化对波束形成器性能影响的问题,相对于频域处理,在有效提高阵列方向图性能同时具有设计简单,运算量小等优点。     

Superconducting sigma-delta analog-to-digital converters

The sigma-delta architecture is the method of choice for designers and manufacturers of analog-to-digital converters (ADCs) for high dynamic range applications. This architecture uses oversampling and precise feedback to generate a shaped spectral distribution of the quantization noise. Subsequent digital filtering suppresses out of band quantization noise, yielding a large signal to in-band noise ratio. This permits the use of quantizers with only a few bits of resolution, most applications use single-bit quantizers. A unique advantage of superconducting electronics is the availability of the flux quantum which can be used to provide quantum mechanically accurate feedback at GHz rates. Josephson digital technology extends the realm of sigma-delta ADCs from MHz sampling rates to GHz sampling rates, from kHz signal bandwidths to MHz signal bandwidths, with comparable or better dynamic range when compared to semiconductor implementations. This paper presents circuits for Josephson sigma-delta ADCs, including single-loop, and double-loop modulators, circuits for quantized feedback, and digital data processing. Experimental results of a double-loop modulator sampling at 1.28 GHz are reported.     

UWB Impulse Radio Receiver Based on Single Bit Quantization

Impulse Radio (IR) modulation is perceived to be a practical means of exploiting the multi-gigahertz bandwidth available for UWB links. However, the RMS delay spreading of indoor channels relative to the transmitted pulse width is typically very large such that several hundred signal samples are required to be quantized and processed for each received pulse. To realize a relatively low power low-complexity receiver of satisfactory performance in low signal to noise ratio environments, signal sampling based on single bit quantization is proposed which is readily realizable at gigahertz rates with modest power consumption. In this paper, the architecture and performance of a coherent IR receiver based on single bit quantization will be analyzed from the perspectives of Rake receiver processing, channel estimation and signal detection. This paper demonstrates that single bit quantization results in a modest manageable performance penalty relative to linear multi-bit sampling. This penalty is readily justifiable in light of the significant reduction in overall receiver complexity.     

A wideband cascaded sigma-delta modulator with improved nonlinearity effects

This work presents a wideband cascaded sigma-delta modulator (CLFSDM) that reduces the nonlinearity effects of components. This architecture offers a new noise-shaping function to achieve high resolution in wideband applications and reduce digital-analogue converter (DAC) mismatch from the multi-bit feedback. Moreover, the error cancellation schemes can be added in the digital circuit part to cancel the coarse quantization errors and thus effectively reduce the non-ideal effects such as DAC mismatch. The mismatches between the two stages, such as in the gain error and pole error, may seriously degrade performance. The blind on-line calibration technique is used to eliminate these imperfect analogue circuit errors in the digital circuit. Accordingly, this architecture can reduce the over sampling ratio (OSR), and the in-band noise can be significantly suppressed to achieve a high resolution in Matlab and Switcap2 simulations. Simulation results indicate this sigma-delta modulator is very efficient in wide bandwidth applications.     

Color error-diffusion halftoning

Grayscale halftoning converts a continuous-tone image (e.g., 8 bits per pixel) to a lower resolution (e.g., 1 bit per pixel) for printing or display. Grayscale halftoning by error diffusion uses feedback to shape the quantization noise into high frequencies where the human visual system (HVS) is least sensitive. In color halftoning, the application of grayscale error-diffusion methods to the individual colorant planes fails to exploit the HVS response to color noise. Ideally the quantization error must be diffused to frequencies and colors, to which the HVS is least sensitive. Further it is desirable for the color quantization to take place in a perceptual space so that the colorant vector selected as the output color is perceptually closest to the color vector being quantized. This article discusses the design principles of color error diffusion that differentiate it from grayscale error diffusion, focusing on color error diffusion halftoning systems using the red, green, and blue (RGB) space for convenience.     

一种光电探测器接口电路的响应特性分析

针对窄脉冲激光时域/频域特性,对窄脉冲激光电路设计进行了详细的分析,包括探测器光敏面面元尺寸分析,以及取样电阻、反馈电容对信号带宽和信号完整性的影响等。为了提高探测系统的信噪比、稳定性等要素,对两种典型的光电接口电路进行了理论分析和软件仿真,得到不同的探测器结电容、取样电阻、反馈电容等参数对窄脉冲激光探测电路光电接口带宽、输出信号幅值、脉宽等响应特性的影响。根据不同种类的探测器及脉冲激光探测信号的频率特性,选取不同的偏置与放大电路,可以使前置光电接口电路的性能达到最佳。     

Resolution enhancement in long pulse OTDR for application in structural health monitoring

To improve the range resolution in inexpensive conventional long pulse optical time domain reflectometer (OTDR) for application in structural health monitoring (SHM) and robotic neural network, the Fourier Wavelet Regularized Deconvolution (ForWaRD) based on the adaptive wavelet method is employed. Since Deconvolution is a noise sensitive process, employing the (ForWaRD) method enhances the signal to noise ratio. Simulation for long pulse OTDR system is done and ForWaRD method is employed to improve the resolution of the OTDR system to the order of several centimeters. In this method the resolution is limited by the bandwidth of detector, bandwidth of electronic circuit, and the sampling rate of analog to digital convertor.     

激光脉冲测距双阈值时刻判别技术研究

在脉冲式激光测距技术中,回波信号幅度和上升时间变化引起的时间晃动误差是影响激光测距精度的主要因素之一.针对时间晃动误差带来的测距精度低的难题,在分析了时间晃动误差和总结一般时刻判别技术的基础上,设计了由高速比较电路,单稳态脉冲展宽电路、脉冲延时电路和快符合电路组成的双阈值时刻判别电路,并对电路进行了误差分析.与一般的时...     

A stationary sampling scheme for multilayer positron tomographs

A stationary sampling scheme applicable to tomographic instruments incorporating two or more detector layers is described and tested. In this concept, the detectors in adjacent layers are angularly offset by half the interdetector distance. By reconstructing in one single slice all lines of response defined by two adjacent rings of detectors, a fourfold increase in the number of coincidence lines is obtained and a uniform sampling distance equal to one-quarter the interdetector spacing is achieved. Whereas this is obtained at the expense of a 100% degradation of the resolution in the axial direction, with the recent breed of PET (positron emission tomography) scanners using nearly square cross section detectors, the resolution loss may be tolerable in many situations. In addition, normal reconstruction of the individual coincidence planes is always possible. The sampling concept was investigated experimentally with the help of the Universite de Sherbrooke PET camera simulator.     

Spatial Quantized Analog-to-Digital Conversion Based on Optical Beam-Steering

A novel optical spatial quantized analog-to-digital converter (ADC) is presented and the performance enhancements through employing this architecture are analyzed theoretically. A high-speed low-jitter ADC sampling clock is provided by a mode-locked laser. A high sampling rate is maintained by avoiding any speed-limiting conversion from optical to electrical domain in an all-optical quantization technique. A high quantization bandwidth is achieved by employing the all-optical quantization technique, benefiting from the high bandwidth characteristics of optical modulation. A high ADC resolution is obtained by using a single-channel quantization configuration and detecting a single image at each sampling step. A high power efficiency is achieved by extracting some portions of the required power from the analog electrical signal and optical sampling clock, directly. Various ADC-resolution limiting factors including the ambiguity of photodetectors, jitter of the optical sampling-clock, the limited beam deflector bandwidth, dispersion, phase modulator nonlinearity/mismatch, noise, and crosstalk have been identified and the contribution of each effect has been discussed.