台灣數位學習數位教學平台 RSS feed provider zh-tw http://lms.xms.com.tw/board.php?courseID=143&f=doclist&folderID=2229 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=12255 Wed, 23 Jul 2014 23:43:29 +0800 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=12254 Wed, 23 Jul 2014 23:42:10 +0800 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=12253 Wed, 23 Jul 2014 23:41:06 +0800 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=10742 Delta-Sigma ADC BasicsAug 13, 2012, 0 comments , in Electrical Engineering, Embedded DesignDelta-sigma ADCs.  Not a new technology by any means, yet still they are regarded by many embedded engineers as mysterious and magical.  In this post, I’ll go through the basics of delta-sigma ADCs, and delta-sigma modulation on a higher level.Understanding delta-sigma ADCs’ benefits compared to different ADCs (SARs, dual slope, etc) will require a broader understanding of delta-sigma modulation and its application in creating an ADC.  The block diagram below describes a delta-sigma modulator (DSM) on a high level.The input signal goes through a subtractor, taking the difference of the input and the output signal (fed through an impulse generator).  Remember, this output is a binary density stream!  When the output signal is 0, the differences passes the input signal straight through to the integrator.  This integrator continues to sum the input until it triggers the compare that follows it (at 0), at which point the output changes from a 0 to Vref.  We can think of this as one, for simplicity, but keep in mind that this block diagram is not implementation specific, so 1 may not make sense for every case.  When the output signal changes to Vref, the impulse block it passes through causes a very large, negative result from the difference, and thus creates a step down in the integrator’s output, causing the compare result to go to 0 again.  All of this can be a little difficult to imagine, so the figure below demonstrates the DSM modulating a DC signal.  In theory, the output goes high for an infinitesimally small amount of time, but let’s assume that this is a clocked digital system with a non-infinite impulse function so that we have a useable output.This difference of sums (delta-sigma, ho-ho!) creates a delta-sigma modulated density stream whose duty cycle is equal to Signal In/Vref.  So, if Signal In is 0.5 Vref, we will see a 50% duty cycle delta-sigma modulated density stream at the output.I can imagine you saying, “OK, that’s cool, but I thought we were talking about delta-sigma ADCs?”  We are, though!  This delta-sigma modulation is most of the work required to make a delta-sigma ADC.  To make this delta-sigma modulator into an ADC, we must simply count the density output and supply a periodic sample pulse to capture the counter’s result and reset it.  This relationship is laid out simply in the block diagram below.This reveals one of the great benefits of the delta-sigma ADC: the process of delta-sigma modulating the input into a density stream and summing it in a counter reduces aliasing of high frequency signals into the pass band greatly.  This means the delta-sigma ADC is more resistant to out-of-band noise than other types of ADC.A practical (simple) implementation of the delta-sigma ADC is implemented below.  As we can see, the elements from the basic DSM block diagram are created here in their analog counterparts.In coming posts, I’ll talk about the benefits and drawbacks of delta-sigma ADCs as compared to other common ADCs (SAR, dual slope, etc.), and also how better, higher order delta-sigma ADCs can be made.  Thanks for reading!http://stuartowen.com/home/2012/08/13/delta-sigma-adc-basics/#!/single_blog Tue, 04 Mar 2014 20:36:18 +0800 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=10319 艾鍗學院-數位電路術科實習作業繳交 Thu, 12 Dec 2013 00:51:58 +0800 http://lms.xms.com.tw/board.php?courseID=143&f=doc&cid=8602 固態繼電器的優點高壽命，高可靠:SSR 沒有機械零部件，有固體器件完成觸點功能，由於沒有運動的零部件，因此能在高衝擊，振動的環境下工作，由於組成固態繼電器的元器件的固有特性，決定了固態繼電器的壽命長，可靠性高。 靈敏度高，控制功率小，電磁相容性好:固態繼電器的輸入電壓範圍較寬，驅動功率低，可與大多數邏輯積體電路相容不需加緩衝器或驅動器。 快速轉換:固態繼電器因為採用固體其間，所以切換速度可從幾毫秒至幾微妙。 電磁干擾少:固態繼電器沒有輸入"線圈"，沒有觸點燃弧和回跳，因而減少了電磁干擾。大多數交流輸出固態繼電器是一個零電壓開關，在零電壓處導通，零電流處關斷，減少了電流波形的突然中斷，從而減少了開關瞬態效應。 ． 無機械式開關之火花問題。． 動作時無噪音。．小型及尺寸共通化、方便安裝。．ON/OFF動作速度快。．具輸入逆向保護。．採用表面貼焊技術，提供最可靠的品質。．具零點觸發方式，可有效避免電磁／高頻干擾。．配安全保護蓋，內裝指示燈（LED）指示其動作。 Wed, 30 May 2012 21:43:06 +0800