A programmable gain amplifier with a DC offset calibration loop for a directconversion WLAN transceiver

A high-linearity PGA(programmable gain amplifier) with a DC offset calibration loop is proposed.The PGA adopts a differential degeneration structure to vary voltage gain and uses the closed-loop structure including the input op-amps to enhance the linearity.A continuous time feedback based DC offset calibration loop is also designed to solve the DC offset problem.This PGA is fabricated by TSMC 0.13μm CMOS technology.The measurements show that the receiver PGA(RXPGA) provides a 64 dB gain range with a step of 1 dB,and the transmitter PGA(TXPGA) covers a 16 dB gain.The RXPGA consumes 18 mA and the TXPGA consumes 7 mA (I and Q path) under a 3.3 V supply.The bandwidth of the multi-stage PGA is higher than 20 MHz.In addition,the DCOC(DC offset cancellation) circuit shows 10 kHz of HPCF(high pass cutoff frequency) and the DCOC settling time is less than 0.45μs.     

976 nm高效率半导体激光器

976 nm高效率半导体激光器是这几年研究的热点,在固体激光器泵浦领域有广阔的应用。通过优化半导体激光器材料外延结构中包覆层和波导层的铝组分,降低了工作电压;通过采用微通道水冷系统,并进行优化降低了热阻,从而提高了室温下的电光转换效率。25℃室温连续测试条件下,1 cm的线阵列(巴条),2 mm腔长,50%填充因子,在110 A下,出光功率为114.2 W,电压为1.46 V,电光转换效率为71%。15条微通道封装成的垂直叠阵,进行光束整形后,获得了室温976 nm连续输出功率1 500 W,电光转换效率大于70%。     

基于AT89C2051的四字LED显示屏的设计

针对现今LED广告屏的广泛使用,应用AT89C2051的可编程功能和串口通信功能,设计一个与计算机通信,可控的LED显示系统。上位机为计算机,下位机为单片机控制16块8×8LED显示屏构成的电路,下位机通过串口与上位机通信,改变显示内容。除了分析其设计思路外,还给出硬件原理图与软件流程图。系统具有设计简单、显示清晰、可靠性高的特点。     

A New Flexible Filter Bank for Low Complexity Spectrum Sensing in Cognitive Radios

Conventional filter bank-based spectrum sensing methods employ uniform discrete Fourier transform filter bank (DFTFB). In this paper, we propose a multi-stage coefficient decimation filter bank (MS-CDFB) for wideband spectrum sensing in cognitive radios. From an initial fixed-coefficient modal filter, a filter bank that has multiple passbands of either uniform or different passband widths can be obtained using coefficient decimation. Design examples show that proposed MS-CDFB offers a complexity reduction of about 30% over the DFTFB while giving a superior sensing accuracy than the latter. The complexity reduction of MS-CDFB over the DFTFB is 85%, if both the spectrum sensors are designed to produce identical sensing accuracies.     

An Area Optimization Method for Digital Filter Design

In this paper, we propose an efficient design method for area optimization in a digital filter. The conventional methods to reduce the number of adders in a filter have the problem of a long critical path delay caused by the deep logic depth of the filter due to adder sharing. Furthermore, there is such a disadvantage that they use the transposed direct form (TDF) filter which needs more registers than those of the direct form (DF) filter. In this paper, we present a hybrid structure of a TDF and DF based on the flattened coefficients method so that it can reduce the number of flip‐flops and full‐adders without additional critical path delay. We also propose a resource sharing method and sharing‐pattern searching algorithm to reduce the number of adders without deepening the logic depth. Simulation results show that the proposed structure can save the number of adders and registers by 22 and 26%, respectively, compared to the best one used in the past.     

Transient electroluminescence determination of carrier mobility and charge trapping effects in heavily doped phosphorescent organic light-emitting diodes

Transient electroluminescence (EL) was used to measure the delay between the excitation pulse and onset of emission in OLEDs based on phosphorescent bis[3,5-bis(2-pyridyl)-1,2,4-triazolato] platinum(ΙΙ) doped into 4,4′-bis(carbazol-9-yl) triphenylamine (CBP), from which an electron mobility of 3.2 × 10⁻⁶ cm²/V s was approximated. Delayed recombination was observed after the drive pulse had been removed and based on its dependence on frequency and duty cycle, ascribed to trapping and de-trapping processes associated with disorder-induced carrier localization at the interface between the emissive layer and electron blocker. The data suggests that the exciton recombination zone is at, or close to the interface between the emissive layer and electron blocker. Despite the charge trapping effects, a peak power efficiency of 24 lm/W and peak external quantum efficiency of 10.64% were obtained. Mechanisms for the electroluminescence and delayed recombination are proposed.     

Controversy over cellular mobile-telecommunication base-station-antenna installations

The two most compelling issues that cause cellular-telephone towers to be so controversial are the public health and aesthetic concerns. People love the wireless convenience and instant connectivity, but no one likes the antenna tower that enables it. The siting of the cellular mobile telephone towers remains a divisive issue, worldwide. Some concerns stem from a lack of personal freedom of choice, in being subjected to the radio-frequency radiation emitted by the tower antennas and its potential health effects. Others have raised concerns about aesthetics and property devaluation. Cell-phone towers with graceful and artistic designs that are tastefully constructed would go a long way toward calming the fears of those who abhor the presence of ugly-cell phone towers looming over homes and businesses. It would be propitious both for the wireless telecommunications industry and the local planning and zoning commissions to collaborate in creating innovative solutions to the design, siting, and installation of cellular telecommunication base-station towers.     

Comments on "A noncoherent tracking loop with diversity and multipath interference cancellation for direct-sequence spread-spectrum systems"

For original paper see IEEE Trans. Commun., vol.46, p.1516-24 (1998 November). In the original paper, the authors presented a noncoherent tracking loop with diversity and multipath interference cancellation to improve the loop performance on frequency-selective fading channels. However, the effects of imperfections in multipath interference cancellation have been dropped out in the statistical analyses, and only evaluated by using computer simulations. The present authors show that such effects can change the error characteristic, at least in the mean sense, and thus make the analyses of jitter performance improper.     

Turbo encoding and decoding of Reed-Solomon codes through binary decomposition and self-concatenation

This paper presents a two-stage turbo-coding scheme for Reed-Solomon (RS) codes through binary decomposition and self-concatenation. In this scheme, the binary image of an RS code over GF(2/sup m/) is first decomposed into a set of binary component codes with relatively small trellis complexities. Then the RS code is formatted as a self-concatenated code with itself as the outer code and the binary component codes as the inner codes in a turbo-coding arrangement. In decoding, the inner codes are decoded with turbo decoding and the outer code is decoded with either an algebraic decoding algorithm or a reliability-based decoding algorithm. The outer and inner decoders interact during each decoding iteration. For RS codes of lengths up to 255, the proposed two-stage coding scheme is practically implementable and provides a significant coding gain over conventional algebraic and reliability-based decoding algorithms.     

A 21-mW 8-b 125-MSample/s ADC in 0.09-mm/sup 2/ 0.13-/spl mu/m CMOS

This paper presents an 8-b two-step subranging analog-to-digital (ADC) using interpolation, averaging, offset compensation, and pipelining techniques to accomplish an effective number of bits of 7.6 b at 125 MSample/s. The 0.13-/spl mu/m CMOS ADC occupies 0.09 mm/sup 2/ and consumes 21 mW.