1. 下列說(shuō)法正確的是 （ ）
A. Java語(yǔ)言不區(qū)分大小寫(xiě)
B. Java程序以類(lèi)為基本單位
C. JVM為Java虛擬機(jī)JVM的英文縮寫(xiě)
D. 運(yùn)行Java程序需要先安裝JDK
2. 下列說(shuō)法中錯(cuò)誤的是 ( )
A. Java語(yǔ)言是編譯執(zhí)行的
B. Java中使用了多進(jìn)程技術(shù)
C. Java的單行注視以//開(kāi)頭
D. Java語(yǔ)言具有很高的安全性
3. 下面不屬于Java語(yǔ)言特點(diǎn)的一項(xiàng)是( )
A. 安全性
B. 分布式
C. 移植性
D. 編譯執(zhí)行
4. 下列語(yǔ)句中，正確的項(xiàng)是 ( )
A . int $e,a,b=10
B. char c,d=’a’
C. float e=0.0d
D. double c=0.0f
The exercise should be finished in English.
2. According to Prof. Zhang s requirement, this exercise mainly focuses on the BER performance of some wireless communication system using specific coding and modulation type through the AWGN channel. Signal-to-Noise ration (SNR) varies from 5dB to 20dB.
The software is capable to simulate space time code [1] for QPSK modulation using different number of state. Examples of generator matrix up to 256 stetes are provided. Variable signal to noise ratio (SNR) might be applied to produce bit error rate (BER) or frame error rate (FER) curves.
Abstract: Specifications such as noise, effective number of bits (ENOB), effective resolution, and noise-free resolution inlarge part define how accurate an ADC really is. Consequently, understanding the performance metrics related to noise isone of the most difficult aspects of transitioning from a SAR to a delta-sigma ADC. With the current demand for higherresolution, designers must develop a better understanding of ADC noise, ENOB, effective resolution, and signal-to-noiseratio (SNR). This application note helps that understanding.
Designers of signal receiver systems often need to performcascaded chain analysis of system performancefrom the antenna all the way to the ADC. Noise is a criticalparameter in the chain analysis because it limits theoverall sensitivity of the receiver. An application’s noiserequirement has a signifi cant infl uence on the systemtopology, since the choice of topology strives to optimizethe overall signal-to-noise ratio, dynamic range andseveral other parameters. One problem in noise calculationsis translating between the various units used by thecomponents in the chain: namely the RF, IF/baseband,and digital (ADC) sections of the circuit.
鎖定放大是微弱信號(hào)檢測(cè)的重要手段。基于相關(guān)檢測(cè)理論，利用開(kāi)關(guān)電容的開(kāi)關(guān)實(shí)現(xiàn)鎖定放大器中乘法器的功能，提出開(kāi)關(guān)電容和積分器相結(jié)合以實(shí)現(xiàn)相關(guān)檢測(cè)的方法，并設(shè)計(jì)出一種鎖定放大器。該鎖定放大器將微弱信號(hào)轉(zhuǎn)化為與之相關(guān)的方波，通過(guò)后續(xù)電路得到正比于被測(cè)信號(hào)的直流電平，為后續(xù)采集處理提供方便。測(cè)量數(shù)據(jù)表明鎖定放大器前級(jí)可將10-6 A的電流轉(zhuǎn)換為10-1 V的電壓，后級(jí)通過(guò)帶通濾波器級(jí)聯(lián)可將信號(hào)放大1×105倍。該方法在降低噪聲的同時(shí)，可對(duì)微弱信號(hào)進(jìn)行放大，線性度較高、穩(wěn)定性較好。
Abstract:
Lock-in Amplifying（LIA）is one of important means for weak signal detection. Based on cross-correlation detection theory， switch in the swithched capacitor was used as multiplier of LIA， and a new method of correlation detection was proposed combining swithched capacitor with integrator. A kind of LIA was designed which can convert the weak signal to square-wave， then DC proportional to measured signal was obtained through follow-up conditioning circuit， providing convenience for signal acquisition and processing. The measured data shows that the electric current（10-6 A） can be changed into voltage（10-1 V） by LIA， and the signal is magnified 1×105 times by cascade band-pass filter. The noise is suppressed and the weak signal is amplified. It has the advantages of good linearity and stability.
All inputs of the C16x family have Schmitt-Trigger input characteristics. These Schmitt-Triggers are intended to always provide proper internal low and high levels, even if anundefined voltage level (between TTL-VIL and TTL-VIH) is externally applied to the pin.The hysteresis of these inputs, however, is very small, and can not be properly used in anapplication to suppress signal noise, and to shape slow rising/falling input transitions.Thus, it must be taken care that rising/falling input signals pass the undefined area of theTTL-specification between VIL and VIH with a sufficient rise/fall time, as generally usualand specified for TTL components (e.g. 74LS series: gates 1V/us, clock inputs 20V/us).The effect of the implemented Schmitt-Trigger is that even if the input signal remains inthe undefined area, well defined low/high levels are generated internally. Note that allinput signals are evaluated at specific sample points (depending on the input and theperipheral function connected to it), at that signal transitions are detected if twoconsecutive samples show different levels. Thus, only the current level of an input signalat these sample points is relevant, that means, the necessary rise/fall times of the inputsignal is only dependant on the sample rate, that is the distance in time between twoconsecutive evaluation time points. If an input signal, for instance, is sampled throughsoftware every 10us, it is irrelevant, which input level would be seen between thesamples. Thus, it would be allowable for the signal to take 10us to pass through theundefined area. Due to the sample rate of 10us, it is assured that only one sample canoccur while the signal is within the undefined area, and no incorrect transition will bedetected. For inputs which are connected to a peripheral function, e.g. capture inputs, thesample rate is determined by the clock cycle of the peripheral unit. In the case of theCAPCOM unit this means a sample rate of 400ns @ 20MHz CPU clock. This requiresinput signals to pass through the undefined area within these 400ns in order to avoidmultiple capture events.
