bwin�ͻ��- 模拟数字转换器的基本原理-National Semiconductor厂商_在线座谈

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主题：模拟数字转换器的基本原理
在线问答：
[问：sqhuang]	与AD421相配的场效应管有何要求，指标如何，代用型号？
[答：Kevin]	I think AD421 should be from ADI company, you can find the answer from them.	[2005-3-10 10:29:56]
[问：yangbinhua]	模数变换器的微分非线性是个什么概念？目前最好的模数变换器这个指标能到什么水平？
[答：Kevin]	DNL and DLE are the same thing and describe the error in step size. This is “small scale” code to code errors.	[2005-3-10 10:32:23]
[问：chenhuyu]	请谈谈AD/DA的动态范围?
[答：Daniel]	Basic dynamic range of ADC, we usually measure the biggest signal and smallest signal so that we can calculate the input dynamic range. And then based on this number, we can choose the right ADC.	[2005-3-10 10:33:02]
[问：haibin]	请比较一下各种转换方式的ADC对于转换效率、精度的影响；请问DAC在电流、电压输出方式中如何保证输出的精度、稳定？
[答：Daniel]	Good question!! We usually use SAR and Sigma-Delta ADC for lower speed, pipeline and flash at higher speed ADC. Sigma-Delta ADC is the most accurate ADC technology so far. For the accuracy of DAC, you need to make sure the stability of reference voltage and output impedance.	[2005-3-10 10:35:41]
[问：xiongshoufen]	想请角专家,能讲讲 sigma-delta 原理吗? 谢谢了
[答：Daniel]	You can realize it in digital way. If you sample a signal for 1000 times and then compute the average value of those 1000 numbers. Then, you can have the normal distribution of those number. At that time, we can know which value is the most possible answer for the sample at that moment.	[2005-3-10 10:37:44]
[问：东走西顾]	ADC的种类有很多，比如∑-△的，SAR的，Pipeline的在实际使用时，应该怎么选择ADC的类型那？
[答：Kevin]	Sigma Delta is often for more resolution but not care the speed SAR is the most used in the actual application due to lower cost,lower power consumption and better speed and other good performance. Pipeline is oftern used for high speed application.	[2005-3-10 10:38:21]
[问：东走西顾]	ADC的种类有很多，比如∑-△的，SAR的，Pipeline的在实际使用时，应该怎么选择ADC的类型那？
[答：Kevin]	have answered it, pls refer to the answer provided before.	[2005-3-10 10:39:12]
[问：format98]	可以介绍一下DAC和ADC的基本原理和工作原理如传输函数，量化，DAC和ADC的结构，工作方式，性能特点以及应用范围.应用系统中使用ADC和DAC的技巧和方法吗？
[答：Daniel]	To be honest, I need to write a book so that I can answer your question. Those basic topologies we have shown them to you. To use an ADC, you need to know how many channels you need, what bit resolution, how fast you need to sample the signal and what interface you should use to connect it to your MCU or DSP.	[2005-3-10 10:39:41]
[问：guanghui]	请问:对于高速设计应用是否用差分方式更好一些？谢谢！
[答：Kevin]	generally yes.	[2005-3-10 10:39:56]
[问：fpi_g]	ADC、DAC常见重要性能指标的含义及一般测试方法（ATE测试方法）
[答：Daniel]	ENOB, INL, DNL, bit resolution, THD, sample rate are all basic parameters for ADC/DAC. for ATE, it"s very complicated to describe them in short sentences. But we measure them item by item.	[2005-3-10 10:41:21]
[问：sunlan117]	如何保证ADC的精度,AD转换的满量程即是电源电压,对于单电源供电,零点的确定和量程都与电源电压有关,如果电源电压波动势必导致转换的误差,电路中如何解决,特别对小信号的采集.
[答：Peter]	Good morning you can choose pre-end AMP which precision match ADC precision. on the other, reference voltage is very importable which shoul match spec requirement for your power consideration, you should take careInadequate Supply Bypassing and Inadequate VA - VDR* Supply Decoupling, for small singal sample, the amp with low noise and gain should match system requirement.	[2005-3-10 10:41:51]
[问：东走西顾]	能否说明一下，在不同的应用场合，对于ADC的指标有什么不同的要求？比如说，哪些应用场合对ADC的INL还有DNL的要求比较高，哪些场合又对SNR和SNDR的要求比较高？
[答：Daniel]	It will depend on your application. I have no general rule so far. But you can specify your application, like Ultrasonic, medical, or industrial control.	[2005-3-10 10:42:29]
[问：unstrung]	在16位的AD转换器件中，如何合理地选择其模拟输入驱动运放
[答：Daniel]	First thing, you need to know the output signal from sensor or signal source. Then, set the highest voltage and lowest voltage of ADC. Then, you can choose rail-to-rail or single ended OP Amp. Based on the input bandwidth, you have to look at the bandwidth parameter of the Amp you want.	[2005-3-10 10:44:29]
[问：mq2001]	How to increase the precision of a flash ADC? Can a flash ADC provide >10 bit precision?
[答：Peter]	Good morning: The precision about Flash ADC is Limited to 10 Bits because of this kink of ADC product technics. thanks for your question.	[2005-3-10 10:45:19]
[问：ldrsxq]	请问有没有8位，双极性，正负5伏供电，转换速度为小于2微秒，并行输出的摸数转换芯片，型号？价格大约？
[答：Kevin]	you can find the correct part in our webiste:WWW.National.com/ADC, you can find not only the part number, but also the key spec, the application note etc.	[2005-3-10 10:46:02]
[问：eguozli]	如何测试ADC和DAC性能？
[答：Daniel]	For commont test, you can use signal generators to test. You need to move from lowest voltage to highest voltage and then use different waveforms, like sine wave, triangle wave or square wave to test ADC. The reverse test methodology to DAC.	[2005-3-10 10:46:07]
[问：ROCZHAN]	专家您好，请问比如说在做数据采集系统的时候，根据什么确定A/D转换的精度？还需要考虑的是什么。谢谢
[答：Daniel]	Based on your input signal.	[2005-3-10 10:46:31]
[问：ROCZHAN]	专家您好，我想提问的是：我在做一个小的系统是如何选用AD转换器，例如采集电压然后交给单片机处理这样
[答：Kevin]	depend on what spec you care for.	[2005-3-10 10:48:15]
[问：tangdogchaos]	请问AD转换速率的理论极限是多少?,目前实际能够作到的最高转换速率是多少? 影响A/D转换的精度都有那些因数? 在使用AD/DA器件进行设计需要注意什么?
[答：Daniel]	To be honest, it"s hard to answer this question. We can not have a perfect ADC for different bit resolution. National can have a technology to have 8bits, 3GHz sample rate now. We need to take care a lot of parameters to design a good ADC system. Basically, all the parameters are based on how much you know the input signal.	[2005-3-10 10:49:57]
[问：kevintang]	模数转换器的过电压保护是如何起作用的？谢谢！
[答：Daniel]	We design a circuit for analog input pin, and conduct those charge to ground inside ADC. It can only provide some level of protection, not to all range.	[2005-3-10 10:51:07]
[问：hurgo]	ADC中如采用放大器，设计时应该注意什么呢，如何保证尽量避免噪声的引入？
[答：Kevin]	match is the most key factor. for noise issue, the op-amp itself and external noise will be the noise distributor as well the ADC itself. it would be much better to select the diff output and lower noise op-amp.	[2005-3-10 10:51:27]
[问：mq2001]	how to reduce the power of pipeline ADC as much as possible?
[答：Peter]	Good morning, Pipeline ADC power consumpition deferent ADC supply is deferent, on the other hand, it is depend on sampling rate and channel number. you know NS ADC Power consumption is very low and package is very small comparing others. thanks!	[2005-3-10 10:51:35]
[问：patriot68]	输入信号幅度变化对AD转换输出的影响。
[答：Kevin]	it would impact the SNR,SINAD,ENOB etc.	[2005-3-10 10:52:38]
[问：cjwd9188]	请问设计一个补偿式交流稳压电源，把采集到的市电信号转换为数字信号，以便于单片机进行智能控制。应该选什么样的ADC。谢谢。
[答：Daniel]	Could you please desribe more about your needs?? I"m not quite sure and understand your problem. If it"s for power meter, that kind of stuffs. I"ll suggest you to use Sigma-Delta ADC because sample rate is not an issue to you.	[2005-3-10 10:53:00]
[问：zhxs]	在语音的ADC转换中，应注意那些性能指标，如何选择
[答：Kevin]	I think Resolution,q noise etc should be paied more attention.	[2005-3-10 10:53:47]
[问：kevintang]	模拟数字转换的转换速率如何计算？谢谢！
[答：Peter]	Good morning: You can refer to the ADC spec which has sampling time and conversion time. thanks!	[2005-3-10 10:54:21]
[问：nkchenliy]	ADC的带宽是如何定义的，如何测量？
[答：Daniel]	Are you talking about input bandwidth or something else?? If it"s input bandwidth, then it will depend how you design the input pad to sample and hold circuit inside ADC. It"s hard to measure by yourself because we use an expensive ATE to do it.	[2005-3-10 10:55:13]
[问：swellcom]	程工，您好，主持人好，我想用TMS320LF2407A DSP连接一个数模转换器，不用GAL译码应如何连接?请问如何做DAC的译码时序图？
[答：Daniel]	Can we discuss it off line?? Please send us an email so that we can think how to do it. We"re not familiar with TMS320LF2407A because it"s TI product.	[2005-3-10 10:56:31]
[问：xulei]	在PCB板上布局时需要注意什么？
[答：Kevin]	it would depend on the ADC speed. for the high speed ADC, we oftern use the single solid GND plane, use the separate power supply,and keep them on the same plane. and do remember that the trace is not just the trace, it should be considered as the trans line.	[2005-3-10 10:57:09]
[问：sun_zhijie]	目前大多数DAC都是用2R-R结构吗？采用2R-R结构，在输出位数很多的情况下，会不会由于IC内部热量不均匀，使得每个2R的值由于热效应而变化，从而使得输出精度降低？
[答：Daniel]	Not yet, right now every DAC maker has her own design and process to resolve this issue. For lower speed one, R-2R ladder is a good solution. But it"s not suitable for higher speed DAC.	[2005-3-10 10:57:48]
[问：zhangxjl]	高速DAC的输出一般都是小信号电平的，DAC是否可能实现直接较大功率等级的射频输出，这样在无线应用中（如短波）能省去功率放大器？在实现上采用大功率电流源加权叠加，这样的大功率DAC在设计上有什么难度吗?
[答：Peter]	Good morning: If you have more power ouput, you can add power amp for wireless application, it is needed. we can do this kind of ADC, but we will take look at market and cost. thanks!	[2005-3-10 10:58:30]
[问：fish272]	对于SAR转换器，如何确定其实际采样频率？资料上只有最大转换速率，不知两者是否一样？
[答：Daniel]	From presentation, you can see that we need 12 clocks to get 12bits data from 12bits SAR ADC. So, it"s hard to talk about sample rate, but we put conversion rate instead of sample rate. The meaning of these two are not exactly the same, but very close.	[2005-3-10 10:59:48]
[问：东走西顾]	比如，在超声波应用场合对ADC的哪些指标要求比较严格？为什么？
[答：Kevin]	关键要求：低功耗，高SNR，多ADC 由于与身体接触，势必会有噪声，所以SNR显得更重要由于在1个系统中有大量ADC，所以ADC尺寸是很关键性 SFDR是重要的，因为需要检测精确的图像（即，差的SFDR可能使医生作出癌症的错误检查）	[2005-3-10 10:59:51]
[问：hzzhangxin]	要采集2路模拟信号，要求采样精度18BIT以上，转换速率25M以上，输出一路DAC控制执行机构，要求12BIT以上精度，1M以上速率，选用什么ADC、DAC型号好
[答：Daniel]	I don"t know the exact part number for this application, National doesn"t have integrated solution for this. But we have ADC12010 can meet your request, 12 bits and 1MSPS.	[2005-3-10 11:01:17]
[问：eguozli]	能讲讲dBFs和dBc是如何定义的吗？
[答：Daniel]	In National Analog University, there is an presentation called "ABCs of ADC". It can answer your question.	[2005-3-10 11:02:11]
[问：luzhenpo]	r-2r的dac是否可以在ref端输入一个信号而实现信号的输出幅度的数字控制，如果可以，ref端输入的信号的频率有什么要求？
[答：Daniel]	Yes, I designed this circuitry before. It will depend on the R-2R ladders and input buffers you choose.	[2005-3-10 11:03:07]
[问：lianlian.liu]	1.转换精度的分析和计算； 2.在实际应用系统中影响转换精度的原因有哪些？如何解决？谢谢！
[答：Peter]	Good morning. Here is list for your reference: ADC resolution SNR and THD The Voltage Reference ... It will depend on system and your circuit, on the other hand, you choose right ADC is very important Thanks!	[2005-3-10 11:04:00]
[问：kkwd]	国半目前最高速的ADC是多少，对于80M以上的ADC在设计时应该注意什么？
[答：Kevin]	more than 1GSPS. pls refer to the answer I have provided for designning the high speed ADC.	[2005-3-10 11:04:01]
[问：东走西顾]	高速ADC中一般都包括一个S/H电路，是不是这个电路对ADC性能的影响很大？怎么提高其性能？比如说减小开关的电荷注入效应等等。
[答：Daniel]	If you"re mentioning about integrated S/H, then it"s done by designers. So, the only thing you can do is to prevent the noise to ADC through power, ground and reference voltage pins.	[2005-3-10 11:04:16]
[问：xlstyle]	积分线性误差（INL），微分线性误差（DNL）分别是如何定义？
[答：Kevin]	DNL and DLE are the same thing and describe the error in step size. This is “small scale” code to code errors. INL and ILE are the same thing and describe the bow in the transfer function. This is “large scale” overall transfer function error.	[2005-3-10 11:04:55]
[问：fish272]	请问：对于SAR ADC 怎样确定其采样频率？如果我想改变起采样频率和resolution（比特数）怎样实现
[答：Daniel]	You can change the input clock during the logic module we show inside presentation foils.	[2005-3-10 11:05:02]
[问：liuxiao98s2]	请问如何简洁地将A/D的结果复用为一路以便于信道传送？谢谢
[答：Peter]	Good morning: You can choose a Multiplexer for multi channels then, one channel output.	[2005-3-10 11:06:10]
[问：encaon]	数据线与CPU控制器总线如何进行隔离能取得好的效果?在PCB布局时要注意什么?
[答：Kevin]	pls refer to my answer for PCB layout.	[2005-3-10 11:07:09]
[问：encaon]	什么是过取样?欠取样?各有何优缺点?
[答：Daniel]	To be honest, it"s hard to pros and cons of over and under sampling. But we"ll do this often because of limitation of ADC which you can find in the market.	[2005-3-10 11:07:23]
[问：xinhr]	如何在实际应用中确定采样频率？
[答：Daniel]	Study your input signal first, and how can you recover the signal from digital data?? If you know it, then you can make sure what sample rate you need.	[2005-3-10 11:08:20]
[问：panjianghong]	在ADC转换时，提供的电源（若怕干扰）是否需要加去耦电容
[答：Kevin]	we oftern place by pass Caps and as near as possible to the pin of power supply.	[2005-3-10 11:08:28]
[问：zhangge]	请问替代ad1674的产品型号？
[答：Peter]	this is ADI AD, we have ADC12041 to replace it. thanks!	[2005-3-10 11:08:33]
[问：wangqh904]	目前，模拟数字转换器所使用的校验技术是什么？精确到什么程度？我对此很关心，谢谢！
[答：Daniel]	It depends on bit resolution you need. In the market, we usually implement so-called self calibration circuit inside ADC. If you"re interesting at this topic, I recommend you to search those papers or articles in Berkeley or Standford University.	[2005-3-10 11:10:11]
[问：w7612]	请问一下用手机电池电压采样ADC，有那几款
[答：Kevin]	we suggest ADC121S101, ADC101S101 and ADC081S101 for battery monitor app.they are fully pin to pin compatible.	[2005-3-10 11:11:29]
[问：cedar]	1、贵公司可提供的ADC最大采样率是多少？ 2、ADC、DAC的数字量最大是多少bit？ 3、在车载应用中，如何解决噪声问题？
[答：Daniel]	1.5GHz without DES (Double Edge Sampling) and 3GHZ with DES at 8 bits resolution. In car system, you need to resolve power noise first.	[2005-3-10 11:11:33]
[问：ldrsxq]	请问专家如果模拟信号为正负2.5伏，想采用单极性的A/D转换芯片，前极如何处理？谢谢
[答：Peter]	Good moring, you can add an Amp circuit for ADC input Span shifting circuits. Thanks	[2005-3-10 11:11:40]
[问：vvvzhzhh]	保持电路对于高频信号，如果充电不充分怎么办？
[答：Daniel]	Then, the part your choose is not suitable for your application if it doesn"t work while you fine tune the Capacitor.	[2005-3-10 11:12:31]
[问：cocow0222]	信噪比，信杂比有什么区别，计算公式呢。各种单位的关系。
[答：Kevin]	SNR = 6.02*N + 1.76 dB, it is related with the resolution.	[2005-3-10 11:12:38]
[问：wwwzhanf]	你好，我想问一下不同种类的ADC对输入信号的阻抗要求是怎麽样的
[答：Daniel]	You can see this parameter at ADC datasheet. Designers will design different Sample and Hold circuit based on different bit resolution (dynamic range) and different sample rate.	[2005-3-10 11:13:36]
[问：wwwzhanf]	关于单极性的ADC，怎样保证输入电压的范围非负，而且对信号的影响小。
[答：Daniel]	If you have question for this, then you need to look at the OP Amp circuits you used in front of ADC. We usually use an OP Amp before ADC just like the page we show in front of presentation.	[2005-3-10 11:14:56]
[问：maeleton1]	什么是管道ADC?它有何特点?
[答：Kevin]	it is called pipe line ADC. The pipelined converter allows us to realize high speed, high resolution ADCS with very low power. A number of stages “build” to final output word in assembly line fashion. Each stage produces a few of the bits of the final output word, plus one or two “extra” bits that are used for digital error correction. The input is digitized to a level less than the full, final resolution and the analog equivalent of that voltage is subtracted from the input of that stage to produce a “residual” voltage. This residual voltage is amplified and presented to the next stage. The output bits from each stage is sent to an error correction circuit, which combines all of these output bits and corrects for errors before sending the final word to the output driver stage. After the first sample is converted and sent to the next stage. Another sample is taken with the first stage. This assembly line method sends the results along, as through a pipeline. Each word is similarly built up, making its way through the pipeline in “D” number of clock cycles. This number of cycles is known as the “pipeline delay” or latency. Immediately after this latency the output word is presented to the output driver circuit. The output drivers exhibit a propagation delay through them, known as the “output delay”, or tOD. A new conversion result is available at each clock cycle, but the data for a given sample is available at the output pins the pipeline delay (or latency) plus the output delay after that input is sampled. Feedback (servo) systems can not tolerate the pipeline delay because it will lead to circuit “hunting”. Although this latency is a disadvantage is some systems, this architecture is a popular one because it permits high speed, high resolution ADCs to function at very low power levels.	[2005-3-10 11:15:15]
[问：xlstyle]	D/A转换器的建立时间（Setting time）、A/D转换器的转换时间（Converting time）一般是多少？
[答：Peter]	basically, it depends DAC/ADC. thanks	[2005-3-10 11:16:30]
[问：mrok]	单端输入和双端输入各有什么有缺点？怎样选择？
[答：Daniel]	The SNR of differential inputs are often better than single ended, but expensive than single ended inputs ADC. I would like to say that you can choose them based on your input signals of sensor.	[2005-3-10 11:16:32]
[问：fish272]	请问：SAR ADC采样频率，转换速率和系统时钟和量化比特数之间有联系吗？
[答：Daniel]	Simple to know that you at least need 12 clocks to convert and get a 12 bits ADC output.	[2005-3-10 11:17:26]
[问：encaon]	目前NS最快的DAC芯片速度能达到多少?精度达到多少位?
[答：Peter]	14bit and 135Msps. thanks!	[2005-3-10 11:17:29]
[问：chenhuyu]	请提供一个最低成本的视频AD/DA解决方案?
[答：Kevin]	it is very hard to provide the solution baed on such simple condition.Anyway,you can check our AFE called ADCS9888 for video application.	[2005-3-10 11:17:30]
[问：翟晓辉]	AD转换器要求严格限制输入模拟电压的值，所以加了两个二极管分别做高低电平钳位。高电平钳位用参考电压Vref合理吗？（芯片集成的参考电压发生器，如果过电压会不会烧坏芯片。）
[答：Daniel]	Possibly it will burn the ADC reference pins. I recommend you to add two bypass capacitors to protect and regulate them.	[2005-3-10 11:18:36]
[问：stick]	DAC的转换速率是否主要受制于输出缓冲器的影响？高速DAC是否一般都采用电流型结构？
[答：Daniel]	Yes	[2005-3-10 11:18:53]
[问：hugoshiuaa]	DAC的输出如何和平滑滤波器连接?对滤波器有何要求?
[答：Daniel]	Look up the bandwidth parameter first.	[2005-3-10 11:19:24]
[问：ljiangf]	请推荐几种16bit正负双向输出的ADC芯片
[答：Kevin]	so far we only have one part for 16bits ,it is ADC16061CCVT	[2005-3-10 11:19:36]
[问：guanghui]	请问：对于高速设计输入信号工作频率为200MHz，我想用带通欠采样进行，请问在芯片选型上应注意哪些问题？谢谢！
[答：Daniel]	If you can use FPGA for it, then I"ll recommend ADC08200 or even higher.	[2005-3-10 11:20:38]
[问：xlstyle]	防止DA/AD的干扰一般都可采取哪些措施？
[答：Peter]	Good morning: here is list for you: right Analog Input stable Voltage Reference good ADC Clock Inadequate Supply Bypassing Inadequate VA - VDR* Supply Decoupling Noisy Components/Conditioning Circuitry Quantization Output to Input Coupling	[2005-3-10 11:20:45]
[问：kevintang]	模拟数字转换的转换精度与哪些因素有直接关系？谢谢!
[答：Daniel]	reference voltage, bit resolution and ENOB of the chip you choose. Besides, you may need to be careful for the layout surrounding ADC.	[2005-3-10 11:21:37]
[问：yammay]	请问ADC器件本身如何抗干扰?在设计中有什么防止自身被干扰的手段和方法要注意哪些方面?谢谢!
[答：Kevin]	generally it is very hard to describe it within limited words.Generally you can pay more attention to the PCB layout.	[2005-3-10 11:21:40]
[问：xlstyle]	DAC的毛刺是如何引起的？
[答：Daniel]	Many reasons can cause it. You need to look at the reference voltage at your system first. Besides, you may check the INL and DNL parameters as well.	[2005-3-10 11:22:53]
[问：ldrsxq]	在pcb设计过程中A/D转换器件的GND是接在模拟地上，还是接在数字地上？对转换结果和受噪声干扰有影响吗？谢谢！
[答：Kevin]	pls refer to my answer for high speed Layout.	[2005-3-10 11:23:04]
[问：xulei]	对于集成有多通道采样保持功能的A/D转换器，如何避免通道间串扰？
[答：Daniel]	It"s hard to avoid them, to be honest. Once the chip is done, then the crosstalk level is fixed. You can choose the discrete solution to make sure you can reach your own target at board level.	[2005-3-10 11:24:19]
[问：lbgy]	如何解决小信号的干扰问题？
[答：Kevin]	you mean the input signal?? diff input for ADC is welcome since it can reduce the common noise.	[2005-3-10 11:24:32]
[问：luogongqiang]	在ADC的选择中,电流输出型和电压输出型的应该怎样选择呢?有何优缺点?
[答：Peter]	depend on your application: right output current and voltage you can refer to ADC Spec to understand their gain , Vin and output current. thanks!	[2005-3-10 11:25:13]
[问：chengping]	如何鉴别一个转换器是否为高分别率？
[答：Kevin]	you can find the answer from the ADC arc, and some spec like SNR etc.	[2005-3-10 11:25:31]
[问：stick]	怎样提高数模转换器中电阻或者电流源单元的匹配程度？
[答：Daniel]	I recommend you to look at the DAC parameter you use carefully, and then test it at your board. We often ignore the coupling capacitor and inductor effects in our PCB, but it may have some impacts to your application.	[2005-3-10 11:25:57]
[问：maeleton1]	PCB布局时，有哪些措施可降低噪声对DAC的影响？
[答：Daniel]	Grounding, power and make sure your DAC is far away from other high speed digital signal.	[2005-3-10 11:26:36]
[问：luzhenpo]	对于r－2r的dac用于控制信号幅度的答复我想知道我从datasheet内的哪个参数可以得知让r－2rladder的频率响应特性？
[答：Daniel]	From the sample rate, you can know it. It often is contrainted by output buffer and input buffers.	[2005-3-10 11:27:53]
[问：h_happy]	把DAC 输出的模拟信号，用AD直接采回，数据失真有多少。如何才能失真最小？我考虑过几个问题： 1。DAC的滤波器 2。采样率 3。位宽。如何才能做到损失最低，成本最低？
[答：Daniel]	Then, your ADC sample rate should be around 10 times faster than your DAC.	[2005-3-10 11:28:31]
[问：starluck]	dsp中内含ＡＤ，它的conversion time (minimum)为５００ns，那摸它的输入信号频率范围限制是多少，在实际工程应用中的是多少那？
[答：Peter]	Good moring, You can take look the single from pre-amp, you should consider that: Settling time vs. ADC sampling rate in DSP. The combined settling time for an op amp and ADC for a full-scale step input to within 1 LSB must be less than the ADC’s specified sampling rate. Thanks!	[2005-3-10 11:28:39]
[问：luzhenpo]	请教主持人，为什么delt－sigma的adc不能有很快的转换速率？
[答：Kevin]	I think it was deponded on segmDelta arc itself. since it include the modulator,comb filter and FIR filter etc, which will limited its speed.	[2005-3-10 11:28:56]
[问：东走西顾]	现在很多高速ADC使用LVDS接口讲并行的数据转换成串行的数据这样可以使得PCB别的布局比较简单。LVDS的接口有两个标准，一个是NS提出的ANSI-664，一个是IEEE的std 1241-2000，这两个标准有多大区别？分别符合这两个标准的LVDS收发器可以正常通讯嘛？
[答：Daniel]	Actually, LVDS is proposed by NS and send it to IEEE. So, they should be the same. If you"re talking about MLVDS, then it"s different.	[2005-3-10 11:30:04]
[问：fish272]	您好，请问对于一个8位SAR转换器，我想改变比特数，如何实现？即实现依次变为8，7，6，5，。。1比特。硬件电路或软件编程，哪个可以实现？
[答：Daniel]	Use software to drop LSB by yourself. DO NOT use hardware to implement it because of price.	[2005-3-10 11:31:01]
[问：wy_niu]	请问语音ADC一般需要多少Bit位的片子？有无推荐型号？
[答：Kevin]	sigma delta ADC is often used for audio or voice application due to hgiher reslution, so far we have not the individual Sigm Delta ADC.	[2005-3-10 11:31:28]
[问：shenghuade]	1，怎样可以买到ADC121S101套件？价格如何？2，本次讲座能否下载？
[答：Kevin]	you can contact our Beijing office Kevin Cheng or shang Hai office Peter Qian for detailes.	[2005-3-10 11:32:44]
[问：yammay]	象ADC这样的混合器件在电路中工作对电源有什么要求?如何测试?
[答：Daniel]	You can look at the presentation about "ABCs of ADC" in National Analog University. There is a foil which is discussing about Power Supply Rejection Ratio. From the formula, you can design your own circuit to evaluate it.	[2005-3-10 11:33:10]
[问：eguozli]	INL，和DNL通常有什么用，一直不太明白。谢谢！
[答：Kevin]	it is for step size and overall transfer function scale	[2005-3-10 11:33:37]
[问：hunk lovesbonnie]	SAR ADC的精度和其内部DAC精度有多大关系?
[答：Kevin]	generally the DAC resolution is higher than ADC reslution.	[2005-3-10 11:34:35]
[问：hzzhangxin]	一般ADC有模拟地和数字地之分，请问怎样布线连接才能获得最好的效果
[答：Kevin]	singel solid GND plane	[2005-3-10 11:35:09]
[问：foxconn]	请问贵公司有没有跟高精度的ＡＤＣ？
[答：Kevin]	so far 16bit.	[2005-3-10 11:35:59]
[问：cjgwz]	一般情况下，在选择AD器件的时候，选带采样保持的转换器好，还是分开选好？
[答：Daniel]	If your application is simple and not so accurate, then I"ll recommend you to use integrated one.	[2005-3-10 11:36:36]
[问：encaon]	如何降低DAC的噪声？对于时钟有何特殊要求？
[答：Daniel]	The spec of input clock will be described in datasheet. Basically, just follow the rising time and falling time of spec, and moreover to prevent the overshooting and undershooting.	[2005-3-10 11:37:42]
[问：xulei]	请比较各种方式ADC的精度和分辨率。
[答：Daniel]	In presentation file, we had already show the distribution of them by speed and bit resolutions.	[2005-3-10 11:38:30]
[问：maeleton1]	多路输入的ADC输入切换和取样频率之间有何关系?
[答：Peter]	Good morning, sampling rate for all ADC channels. it will depend on Acquisition Time, Throughput Time=Conversion Time + Acquisition Time thanks!	[2005-3-10 11:39:27]
[问：luogongqiang]	如果降低温度对DAC性能的影响?或者提高温度使用范围?
[答：Daniel]	You can see those spec in datasheet of ADC. You need the accurate spec after those makers test the chip at ATE.	[2005-3-10 11:39:28]
[问：silenyang]	测试ADC的SNR时，对clock的jitter有什么要求？对输入信号的SNR有什么要求？谢谢！
[答：Kevin]	clock jitter is very important for your SNR.You can find the answer in our ADC website.	[2005-3-10 11:39:38]
[问：hzzhangxin]	ADC转换速度25M以上，转换精度18位以上，不知道这样的ADC有没有
[答：Peter]	Sorry, Now we do not have . thanks!	[2005-3-10 11:40:14]
[问：guanghui]	请问：在高速实际设计中应注意哪些问题？谢谢！
[答：Kevin]	pls refer to answer I provide before	[2005-3-10 11:40:49]
[问：hzzhangxin]	我想用25M以上速度，18bit以上精度，不知道这样的ADC有没有
[答：Kevin]	so far we have not yet.	[2005-3-10 11:41:32]
[问：lindylong]	模拟数字转换器在工业应用方面的趋势
[答：Daniel]	Accuracy is the most important feature, and sample rate may not be the big concern in industrial control. But for some high speed data acquisition system, people may ask for higher sample rate. The final trend will be the input voltage sewing.	[2005-3-10 11:43:08]
[问：xlstyle]	请谈谈各种类型ADC的优缺点！逐次逼近SAR、积分---
[答：Kevin]	SAR ADVANTAGES: Low Power Single Comparator DISADVANTAGES: Limited to About 5 Msps Integration ADC ADVANTAGES: Noise Immunity High Resolution Possible Can Notch Out Unwanted Frequencies Handles Low Level Inputs Well DISADVANTAGES: Very Slow Reliance upon Accurate Components Limited to D.C. and Low Frequency Inputs	[2005-3-10 11:43:15]
[问：micheas]	如果我想得到你们的demo板是不是可以免费向你们索要呢
[答：Daniel]	You can contact with our sales office to see if we can provide you or not. For some ADC, we need to follow US Expoert Control Law.	[2005-3-10 11:43:59]
[问：5812114]	A/D D/A 模块误差使用不同厂家的变送器信号输出都是4-20毫安用同一主板显示采集的数值为何不一样? 侯国轩13837478479
[答：Peter]	Mornging: Pls refer to their input range whether their requiements are deferent. thanks!	[2005-3-10 11:44:20]
[问：qilin315]	随着采样频率的提高，以后模拟电路和数字电路还会有区别吗？
[答：Daniel]	Over some critical mess, like about 300MHz, all digital circuits are running at analog way.	[2005-3-10 11:44:48]
[问：覃小林]	AD器件的转换分辨率怎样确定？
[答：Kevin]	SNR = 6.02*N + 1.76 dB also you can get the ENOB form the SINAD	[2005-3-10 11:44:50]
[问：vvvzhzhh]	对比较器的输出要求是不是要求很高？否则精度怎么保障？
[答：Daniel]	If you use ADC, then you don"t need comparator at all. If you"re talking about the comparator to make an ADC, then the answer is yes.	[2005-3-10 11:45:40]
[问：luzhenpo]	为什么在national的网站上找不到1G以上的adc？
[答：Kevin]	the part number is ADC08d1000, ADC081000	[2005-3-10 11:45:53]
[问：曹振生]	ADC的功耗是多少
[答：Kevin]	depend on which type ADC. SAR ADC will have less power consumption but pipe line ADC has more power than SAR ADC.	[2005-3-10 11:47:08]
[问：fish272]	adc 转换速率单位有hz,sps, 他们一样吗？
[答：Peter]	SPS 是采样,Hz是它的单位.	[2005-3-10 11:47:48]
[主持人：ChinaECNet]	恭喜您，杭州朗杰测控技术开发有限公司的hzzhangxin经过电脑抽奖您在本次座谈中获得一部MP3播放器。请网名为hzzhangxin的用户与中电网联系(8610-82888222-7008 或 lilin@chinaecnet.com)。	[2005-3-10 11:47:49]
[问：lbgy]	取样保持时间和取样频率之间的关系如何计算?一般为多少比例?
[答：Daniel]	You need to keep those input level same after you finish the conversion. It is controlled by ADC itself, and you don"t need to concern about it. If you want to use external S/H chip, then you had better make them the same.	[2005-3-10 11:49:09]
[问：kkwd]	请推荐几个80M 以上适合数据采集用的ADC型号
[答：Kevin]	we can provide you many ADC which can meet your speed. you can find the part number from our website: WWW.National.Com/ADC	[2005-3-10 11:49:29]
[主持人：ChinaECNet]	祝大家事业有成、生活愉快！欢迎多提宝贵意见，欢迎关注中电网，下次再见。	[2005-3-10 11:50:05]
[问：yangtao shuixiang]	现在最高的精度是多少
[答：Kevin]	released products:16bits	[2005-3-10 11:50:06]
[问：fish272]	我的输入信号是sine wave,square wave,triggle signal,因为是AC信号，双极性信号，在选ADC时要注意什莫？想用8比特并行的SAR。信号由波形产生器产生，ADC之前用加防混淆滤波器吗？
[答：Daniel]	Yes, you need filter or use OP Amp before ADC. The simplest way is to use differential input ADC with Op Am as antenuator.	[2005-3-10 11:50:27]
[问：hzmxr]	我的气象数据仅有3微安,附近有雷达,如何解决抗干扰?
[答：Daniel]	The best way is to use ground shilding to prevent noise.	[2005-3-10 11:51:08]
[问：luogongqiang]	如何正确选择DAC?转换速率和带宽应如何取舍？
[答：Peter]	you can take care resolution and convertion time SNR, THD, and other AC performation you shoud conderate depending on your application.	[2005-3-10 11:52:28]
[问：starluck]	我使用ＡＤ的输入电压范围是０～３.３Ｖ，但我的输入信号是零点几个毫，伏级，前端需要加放大，能建议几种温度范围在－４０～１２５间的运算放大器和仪表放大器吗？
[答：Daniel]	We have LMH2011/2012/2013, and they are all presicion OP Amp which can be used in equipment.	[2005-3-10 11:53:53]
[问：luogongqiang]	视频应用的ADC和DAC如何选择?它的关键性规格是哪几个方面呢？
[答：Peter]	this application need high speed adc and dac. you consideration can cover: Resolution, speed and SNR, THD and other AC performance.	[2005-3-10 11:54:46]
[问：kevin.zheng]	DAC的毛刺应如何消除？
[答：Peter]	Here is list for you: Inadequate Supply Bypassing Noisy Components/Conditioning Circuitry Quantization Clock Output to Input Coupling	[2005-3-10 11:56:22]
[问：lixiaobai]	转换一个模拟信号到数字信号要多长时间？
[答：Daniel]	It depends on what techology you"re using. For flash and pipeline, it takes 2 to 3 clocks. But it takes a lot of time to convert signal with SAR and Sigma-Delta ADC.	[2005-3-10 11:56:46]
非在线问答：
[问：]	r-2r的dac是否可以在ref端输入一个信号而实现信号的输出幅度的数字控制，如果可以，ref端输入的信号的频率有什么要求？
[答：]	yes, but it depends on what kind of input buffer you're using.
[问：]	SNR是如何定义的？
[答：]	The ratio of input signal over noise above the signal.
[问：]	单电源和双电源的DAC在性能有何区别?
[答：]	No big difference actually, but may easier for you to design your system at some cases.
[问：]	"模拟数字转换器的應用領域?"
[答：]	Just like I said, it's the bridge between real world and computer world.
[问：]	模拟数字转换器选用该注意那些问题？
[答：]	I'll suggest you to look at your input signal first, and then decide SNR and use SNR to calculate the bit resolution for your ADC.
[问：]	目前的D/A能达到多少位
[答：]	There are many 16bits DAC in the market now.
[问：]	你们AD转换器的最大速率有多大
[答：]	1.5Giga Sampling Per Second
[问：]	请简要介绍模拟数字转换的几种方式
[答：]	You can look at our presentation foils or file in National's Analog University
[问：]	请谈谈Sigma-dailta 模数转换器的基本工作原理。
[答：]	Please refer my answer to another question but same as yours.

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