| 主题: 驱动精密ADC：如何为您的ADC选择最合适的基准电压源和放大器? |
| 在线问答: |
| [问：callhxw] |
如何评定一颗ADC非线性？丢码？ |
| [答：Jing] |
you can use ADC"s INL and DNL parameter to evaluate the non-linearity
and you can also use ENOB parameter to check code loss. Thanks!Generally
ENOB releated with ADC"s SNR |
[2006-2-28 10:32:08] |
| [问：吉星] |
在差分输入时，不考虑直流，使用差分放大器和变压器哪个更好． |
| [答：Mariah] |
Transformer is better for the better noise and distortion performance,
especially in very high frequencies. |
[2006-2-28 10:32:14] |
| [问：Jane Yang] |
请问应如何处理板级噪声对于高精度AD的影响？特别是输入部分的噪声？ |
| [答：Jing] |
This is a good question and it"s very difficult to answer. Generally,
You should consider all the input noise derived from sensor/AMP/BUFFER.
You can also use a LPF to reduce the input noise. Remember the BGP of
AMP should be 100x of ADC"s throughput. Thanks! |
[2006-2-28 10:34:30] |
| [问：石林艳] |
AD变换的参考基准源很重要，对模拟供电电源和数字供电电源的要求也很高吗 |
| [答：Rui] |
模拟供电电源，和数字供电电源相对基准源来说，精度要求相对较低，一般情况下用10uF的电容和0.1uF滤波即可。 |
[2006-2-28 10:34:31] |
| [问：zcs_1] |
请解释一下，分辨率和转换精度之间的区别 |
| [答：Mariah] |
For conversion accuracy, it involves many aspecs. For example, INL,
DNL, offset, gain error. |
[2006-2-28 10:34:46] |
| [问：Leemour] |
對不起能否講一下什麼是：RAIL TO RAIL，這個我一直不太明白。 |
| [答：Xiangquan] |
轨到轨指输入轨到轨，或输出轨到轨，具体指的是输入信号或者输出信号的范围基本接近于电源，譬如电源是+-5V，输入信号或输出信号可以达到+-4.9几V以上 |
[2006-2-28 10:35:25] |
| [问：jlwg] |
很多种adi的a/d转换器件都自带有标准电压源，请问是使用器件自带的标准电压源好还是另外使用独立的标准电压源更精确？
另外使用ad7710时，每次转换通道后的第一次转换结果是否是有效的？ |
| [答：Troy] |
Use an independant reference to get the highest accuracy and lowest
temperature drift. It depends on how much accuracy your application
needs over temperature. |
[2006-2-28 10:37:14] |
| [问：xwlcba] |
您提到驱动AD的运放增益带宽积要求大于100倍采样速率,请问对运放的转换速率有何具体要求? |
| [答：Troy] |
To get the lowest distortion (THD), we recommend using an amplifier
with at least 100x gain-bandwidth product greater than the sample rate. |
[2006-2-28 10:39:36] |
| [问：bly1979m] |
本人最近做了一个项目用于精确测量温度的，就用到了这两种器件！请推荐几款贵司产品？并说说它的大概价格是多少？ |
| [答：Jing] |
It"s depend on the accuracy of your system requirement. I am pleased
to recommend that you can use our ADR421+AD7799. For price, you can check
it on our web or consult our distributor according to your volume. Thanks! |
[2006-2-28 10:39:40] |
| [问：guahuahua] |
选用AD7788时，能选择的最适当的参考基准源是哪一款 |
| [答：Mariah] |
You can try the software we recommended in the presentation "reference
selection wizard". You can download it from the link of http://www.analog.com/Analog_Root/static/techSupport
/designTools/voltageReference/download.html
|
[2006-2-28 10:41:33] |
| [问：arzhiy] |
RC滤波器设计在ADC前就会出现相位漂移的情况，这样采集到的信号是一个失真的，是这样的吗？ |
| [答：Troy] |
The RC filter will not add any distortion to the signal. The
RC filter will reduce noise at frequencies higher than its cutoff frequency. This
improves ADC performance because it reduces out-of-band noise to the ADC
input. |
[2006-2-28 10:44:33] |
| [问：yz_yjg] |
我们的有一个双通道数字示波器产品，当进行垂直移位时，即施加给AD9288的直流电平改变时，发现发现基中一个通道在LCD屏上的某些区域的基线变粗（这有规律，如每间隔16或32出现），有2mm到8mm左右不等，更换AD9288即可。大多数是其中的一个ADC有问题，我们希望基线在屏幕上移动时（不加信号），扫描基线的不要发生粗细变化，请问是什么原因？AD9288能完全消除这种现象吗？ |
| [答：Mariah] |
We need to know more details about your circuit. Would you please send
your question and schematic in details to china.support@analog.com, and
then our engineer will help you on that. |
[2006-2-28 10:45:35] |
| [问：callhxw] |
双极性输入信号，采用OP转换为单极性的到ADC，设计时应关注哪些？ |
| [答：Jing] |
First , you can select AD8129/AD8130 to realise the function. But this
will reduce the ENOB. I suggest you use differential input ADC too. You
should consider the noise from the AMP and the GBP of the AMP.You had
better to select a high GBP and CMRR and low noise AMP. Thanks! |
[2006-2-28 10:45:35] |
| [问：Jane Yang] |
which reference is better: external or on-chip,
for high speed (40~105M) and 12~14bit ADC? |
| [答：Troy] |
External references give better initial accuracy and lower drift over
temperature. Using the on-board reference or an external one
depends on the accuracy you need in the application. Generally
speaking, the higher the ADC resolution (# of bits), the more likely you
will need an external reference. |
[2006-2-28 10:46:16] |
| [问：liu.gy] |
1、就ADI的产品而言，请给出“基准电压源+ADC”的两种方案：分离与集成 两个方案的优缺点？
2、运放到ADC之间什么时候需要加滤波处理？如果加滤波处理，请给出滤波的方式及性能比较？ |
| [答：Xiangquan] |
1。集成主要带来方便，但是往往由于工艺的限制往往不能发挥转换器的最高性能，如果选择合适的外部参考源，则可以比较好的发挥转换器的性能
2。运放与AD之间的滤波主要为的是滤除噪声，抗混叠，以及给ADC的转换产生的瞬态能量提供缓冲，一般一阶RC低通滤波即可，或者对于带通滤波，可以根据自己的要求进行设计 |
[2006-2-28 10:46:34] |
| [问：chenhaifeng] |
放大器的PSRR是否与外电路及输入信号无关？ |
| [答：Haoran] |
PSRR主要是电源对信号的影响，与外电路和信号无关 |
[2006-2-28 10:47:12] |
| [问：hzluoping] |
请问：1）精密ADC的数字地和模拟地的正确接法及对ADC转换精度的影响？ 2）在单片机系统应用时，对精密ADC的启动和数字信号的输出的控制
有何要求？ |
| [答：Jing] |
1> you should consider the system current. If the digital current
is small, you can seperate digital GND and analog GND and combine them
together in one point. If the digital current or noise is very large,
you can also look ADC digital GND as analog GND.
2>I don"t know what you mean. Generally ,some of our ADC has hardware
start and software start selection. |
[2006-2-28 10:48:39] |
| [问：arzhiy] |
常用的RC往往本生噪声也很大，这样且不是更加增加了采样的噪声？ |
| [答：Haoran] |
噪声主要来源于电阻，实际上在可能的情况下或电路稳定的前提下，尽量增大电容可以提高噪声性能。 |
[2006-2-28 10:48:50] |
| [问：boclandc] |
我采用了AD7671,测试8通道的线性电子尺(等效线性电阻),请问有什么好的多通道切换,我采用了二片MAX4052后面通过AD620做驱动,但是切换至稳定时间需达10uS,在切换速度上非常不理想.不知贵公司有否这样的方案,使切换速度小于或等于2uS?谢谢!! |
| [答：Mariah] |
ADI has many new mux and switches which has better performance, like
ADG121x, ADG13xx and ADG14xx. Also the settling time also depends on your
circuit. You can send your schematic and question to china.support@analog.com.
Our engineer can analyze your circuit and give out the solution. |
[2006-2-28 10:49:42] |
| [问：ecnanjing_EBY7E] |
请问,电压基准的精度和温度系数对AD的精度的影响的换算关系是怎样的? |
| [答：Haoran] |
你可以在今天的资料中找到，并且可以从我们的网站上下载 |
[2006-2-28 10:50:00] |
| [问：hzluoping] |
模拟地和数字地的接法对ADC影响大，如何作好接地？ |
| [答：Rui] |
地的接法一般有两种，1。把地平面分割为模拟地和数字地，或者一层数字地，一层模拟地，然后共同接到共地点。2。不分割模拟和数字地，使用多点接地。
对于第一种情况，注意数字地层和模拟地层不能重叠。
对于第二种情况，要提供尽量多的接地点。 |
[2006-2-28 10:50:14] |
| [问：amatist] |
基准源有齐纳二极管和带隙电压基准等几种,它们有何优缺点? |
| [答：Troy] |
References built using bandgaps have lower temperature drift, but they
are more complicated and more expensive. Zener references are
usually less expensive, but have more noise and may have lower initial
accuracy and higher drift over temperature. |
[2006-2-28 10:50:22] |
| [问：amatist] |
对电压基准源的要求主要有那些指标?如何选择电压基准源? |
| [答：Jing] |
Intinal accuracy, temperature drift is two of the key factor. You can
according to your system error requirement and download our REF+CONVERTER
wizard to select the corresponding REF. Thanks! |
[2006-2-28 10:50:22] |
| [问：elmer] |
放大信号中出现大的脉冲信号，怎样去除这个信号？ |
| [答：Haoran] |
你可以先在运放前增加低通滤波器。 |
[2006-2-28 10:51:00] |
| [问：wzj0713] |
pA~mA的高动态低变化速率输入的信号调理拟使用ADI产品ad8304，现在需咨询的是如何最小限度的减小引入噪声（从PCB版图、工艺和电路处理两方面）。 |
| [答：Jing] |
You can use AD8304 to interface a PIN and converter current to voltage.
To minize the input noise, you should select a better PIN--this is the
first noise source. Then you should select high accuract resistor and
capacitor . Of course, multi layer PCB is better to minize the inout noise. |
[2006-2-28 10:53:35] |
| [问：yz_yjg] |
ADI有没有可编程的基准电压源?型号? |
| [答：Troy] |
We do not have a digitally programmable voltage reference today. The
AD8555 is a digitally programmable instrumentation amplifier with a built-in
voltage reference. You could use this just as a programmable
voltage reference by grounding the +IN and -IN pins. |
[2006-2-28 10:54:40] |
| [问：hanxin] |
在使用ADI的AD转换器的时候,如何确定是否需要前端的运放? 如何根据不同的AD确定需要哪一种运放?如何处理前端的RC
? 是否可以分别就AD7865和AD7656来说明? |
| [答：Haoran] |
AD7865是14bit的ADC，输入端为低阻，所以前端必须选用双极性的运放。整个带宽内的噪声要满足14比特ADC的要求。OP497/OP4177是不错的选择。
AD7656是16bit的ADC，输入端为高阻，所以模拟前端可用高性能的双极性运放，也可以不用。但我们建议采用，这样信号的完整性比较好。当然运放的选择，电路的设计要满足噪声要求。OP4177/AD8674是不错的选择。 |
[2006-2-28 10:56:03] |
| [问：zcs_1] |
Ad8138使用应注意哪些地方，好像电阻不能设置很大的阻值？ |
| [答：Jing] |
AD8318 is our RF LOG-AMP. I don"t know which resistor you are mentioned.
For better performance, you should pay attentation to the impedance match
of input/output circuit. This is the very important factor. |
[2006-2-28 10:56:11] |
| [问：hanxin] |
选择基准的时候,我们主要需要看那些参数?哪些参数决定一个基准是比较好的? |
| [答：Troy] |
Initial accuracy is the easiest spec to compare. Temperate
drift in ppm/C is also important. If you are using a portable
application, supply current will be important. For 16+ bit
ADC applications, the output noise is also important. |
[2006-2-28 10:56:46] |
| [问：shandong] |
降低噪声的主要措施和手段都有那些?并且比较经济和实用的有那些? |
| [答：Xiangquan] |
不确定您的应用场合是什么，总体来说，你可以：1.选择高性能的器件，2.对感兴趣的带宽进行滤波，3.模拟地和数字地的分割(layout issues) |
[2006-2-28 10:57:20] |
| [问：zrg175] |
请问用电感进行滤低频的话，电感的值怎样选择，有什么规律吗？谢谢！ |
| [答：Rui] |
一般情况下，电路中使用电容滤波，高通滤波器的截至频率为1/(2Pi*RC).
如果您有特殊需要，必须使用电感进行滤波，请把具体的情况和问题提供给 china.support@analog.com 寻求更详细的帮助 |
[2006-2-28 10:57:25] |
| [问：luyisa] |
在多通道测量中，模拟开关出来的信号是否能直接进ADC?若中间要接运放的话，对运放的要求有什么？ |
| [答：Jing] |
Yes , you can interface MUX and ADC together.
if you want to get better performance, you can add AMP before the MUX
for every channel. |
[2006-2-28 10:57:51] |
| [问：石林艳] |
怎样提高A/D变换的有效位数，尤其对高频的变换？ |
| [答：Haoran] |
在选定一定位数的ADC之后，前端信号的处理要满足精度要求，参考电压的噪声要尽量的小，对于高速ADC,时钟的精度也是要考虑的重要因素。 |
[2006-2-28 10:58:34] |
| [问：xiexinpo] |
请问：对于AD9235BRU-40,选择3.3V单电源，用AD8137做前级缓冲并转换成差分输出（1.625V 参考电压），然后用AD8330ARQ做增益调整是否可行？应注意哪些问题？是否要增加低通滤波器？其低电压电源对于模数转换器的线性和动态范围有多大的影响？谢谢！ |
| [答：Mariah] |
There would be no problem for use the combination of these parts. For
low voltage application, use rail to rail output amplifiers will increase
the dynamic range. As you know, AD8330 is a rail to rail output amplifier.
There should be a anti-aliasing filter before the ADC. You can find the
typical connection of the AD8330 and ADC. You can just add a R-C filter
between AD8330 and the ADC. |
[2006-2-28 11:00:56] |
| [问：tjshen] |
高精度ADC、电压源和放大器的长期稳定性的测量方法及其设备的要求。 |
| [答：Troy] |
We characterize at least 300 units for 1000 hours before qualifying
a product family released for sale. Offset voltage is measured
before the 1000 hours and after the 1000 hours. The difference
in offset voltage is the drift. We calculate long-term drift
based on these numbers. Stability is verified on the bench
by observing the output voltage with an oscilloscope. |
[2006-2-28 11:01:04] |
| [问：caitouc] |
精密应用时是否需要对电源50Hz进行滤波?如何实现? |
| [答：Xiangquan] |
一般心电信号（mV级信号）、脑电信号（uV级信号），以及一些小信号的测量需要进行工频抑制，因为工频信号往往可以引起伏级干扰；如果对50Hz进行滤波，主要有软件和硬件的方法来实现notch
filter，也可以利用提高系统的共模抑制比(CMRR)来实现。 |
[2006-2-28 11:02:38] |
| [问：arzhiy] |
对于24bitADC我们一般选取什么样的基准源，例如采用AD公司的哪个型号？ |
| [答：Troy] |
I recommend the ADR420 family. |
[2006-2-28 11:02:53] |
| [问：Jane Yang] |
To evaluate your AD, such as AD9236, what
kind of clock source and signal source should be equiped? could you give
some examples? |
| [答：Jing] |
For clock, you can use ADF4360-X or ADF411X+VCO or AD9510+VCO . For
signal source , you can use some instrument such as rohde-schwarz company"s
instrument . |
[2006-2-28 11:03:01] |
| [问：engronger] |
运算放大器有时候会有温漂的现象,请问调整温漂有什么好的办法? |
| [答：Haoran] |
对于普通运放，你可以看到Offset Drift这个参数，他的大小代表了温漂。当然，你还可以选用我们zero drift的放大器，AD8628/9/30是目前最好的放大器。 |
[2006-2-28 11:03:57] |
| [问：lsqbank] |
AD转换芯片的Gain Error，一般最坏情况都能达到0.25%FSR，请问，如何减小这一误差，Gain
Error Match是否是在已经进行调整后，AD芯片的Gain Error所能达到的最好性能？ |
| [答：Mariah] |
Generally speaking, gain error is a linear error. So you can use calibration
to remove this error. The main concern of using the ADC is the gain nonlinearity
error. Nonlinearity error is difficult to remove. |
[2006-2-28 11:04:30] |
| [问：ecnanjing_EBY7E] |
双极信号转为单极信号要引入直流分量,对AD的精度有无影响? |
| [答：Troy] |
Not if you use an instrumenation amplifier. If you use external
resistors, the accuracy is only as good as the resistor matching. |
[2006-2-28 11:04:40] |
| [问：zcs_1] |
请问如何根据设计来选择合适的位数的AD或DA芯片 |
| [答：Rui] |
主要是根据您的系统所需要到频率和精度所决定的。
首先确定信号的工作频率，选择能够满足采样速度的AD或DA，
其次确定信号的幅值，选择能够提供足够输入/输入范围的ADC，同时可根据需要的精度或允许的误差范围选择放大器的位数。
还有输入/输入为差分或者单端，输入的信号的路数，有无内置参考源，内置缓冲等等都可以作为选择的标准。 |
[2006-2-28 11:04:51] |
| [问：kivin_G] |
现在的电压基准源最低电压能达到多低?有没有电压为0.6V的电压基准源? |
| [答：Troy] |
Usually about 1.2V. I am not familiar with a 0.6V reference. You
could use a forward-biased diode to generate 0.6V to 0.7V. |
[2006-2-28 11:05:46] |
| [问：sxfs1984] |
如何降低运算放大器输出的波纹?应该考虑那方面的因素? |
| [答：Haoran] |
首先你要先考虑这个纹波是从哪里来的，然后再确定在怎么处理。 |
[2006-2-28 11:06:26] |
| [问：ecnanjing_EBY7E] |
请问放大器的相位失真如何控制? |
| [答：Mariah] |
you can use compensation circuits to do that. |
[2006-2-28 11:07:06] |
| [问：amatist] |
向多个电路提供基准电压源时,如何扩充基准电压源的输出能力? |
| [答：Troy] |
One way to increase output current is to use a unity-gain buffer at
the output of the reference. This is a very common technique
for improving the reference output drive. |
[2006-2-28 11:08:21] |
| [问：sxfs1984] |
什么情况下要选择隔离放大器?如何选择? |
| [答：Mariah] |
When there are potential high voltage difference between two sides,
you need to isolate them. For example, medical applications, motor control
applications. |
[2006-2-28 11:09:32] |
| [问：hzluoping] |
对直流纳级弱信号放大时，增益带宽积问题如何看 |
| [答：Rui] |
一般情况下，对于小电流信号，放大倍数要求都会比较大，例如1000，如果信号频率同时又比较高，就要注意增益带宽积的限制的问题。
增益带宽积为信号频率和放大倍数的乘积，在选择器件的时候要注意该数值不能超过放大器的给出的增益带宽积参数 |
[2006-2-28 11:09:55] |
| [问：woodxp] |
对于低频信号也需要加抗混叠滤波器吗？ |
| [答：Mariah] |
Yes. |
[2006-2-28 11:10:05] |
| [问：htc703] |
1.放大器的噪声en的峰峰值(Vp-p)和有效值有联系吗？怎么换算？
2.在24-bit数据采集系统设计中应该注意哪些问题？ |
| [答：Haoran] |
1。Vp-p=6.6Vrsm
2。在sigma-delta ADC中，SNR是比较重要的参数。设计中主要应注意前端的处理，以及版图方面的考虑。 |
[2006-2-28 11:10:07] |
| [问：bly1979] |
1。请问目前性价比最高的ADC是哪一款？大概价格是多少？
2。位数最大的ADC是哪一款，多少位？大概价格是多少？
3。低功耗ADC是哪一款？最低功耗多少？大概价格是多少？ |
| [答：Jing] |
1. It"s very hard to answer this question. It should according to your
application such as your accuracy,error ,power supply,throughput etc.
2. Now we have 24bit ADC such AD ad7799 etc
3. AD7680 is a good selection for portable instrument---3mW For
price,please present your volume and consult our distributor our check
it on our web. Thanks! |
[2006-2-28 11:11:10] |
| [问：lewisflame] |
专家您好、主持人您好，ADC基准经过放大器驱动后，通过镜像结构输出基准电流，每一对镜像管的版图是不是最好使用相同的单条尺寸：W不匹配会不会增大失配？ |
| [答：Troy] |
Yes. It is a good idea to use the same metal width.W不匹配会会增大失配 |
[2006-2-28 11:11:31] |
| [问：xiexinpo] |
自动校零放大器对ADC的噪声有多大影响？ |
| [答：Troy] |
Auto-zero amplifiers have slightly more noise than non-auto-zero amplifiers. In
many cases, the noise will still be much lower than 1LSB. Many
customers use auto-zero amplifiers and do not have any problems with noise. Auto-zero
amplifiers have no drift over temperature and almost zero offset voltage. I
recommend using them when possible. |
[2006-2-28 11:15:06] |
| [问：woodxp] |
在ADC前加RC滤波，不会影响ADC的性能吗？因为ADC一般有采样保持电路，在其前面并上一个电容，则会影响其采样保持时间吧？ |
| [答：Haoran] |
加RC滤波不会影响ADC的性能，相反还会提高它的性能和稳定性。ADC内部一般有采样电路，外部的电容可以在每次采样的时候提供快速的充放电，提高它的精度。一般ADC外部都会有运放来驱动，所以电容不会影响保持时间。 |
[2006-2-28 11:16:35] |
| [问：shandong] |
为了降低噪声在布PCB板方面应注意那些问题. |
| [答：Troy] |
I suggest using a 4-layer board. One internal layer is ground,
and the other internal layer is power. We recommend using separate
digital and analog ground and power planes. Many times, you
can use a split plane to keep digital currents separate from analog currents. This
greatly improves noise performance. |
[2006-2-28 11:17:11] |
| [问：cola] |
AD８０３１是一个很好的信号调理运放，它具体可以实现哪些调理？ |
| [答：Haoran] |
AD8031信号带宽和噪声参数都比较好，所以可以作为前端信号的处理以及参考电压的驱动。 |
[2006-2-28 11:17:48] |
| [问：ddac87] |
放大电路的频宽问题: 我们知道引入负反馈可以拓展放大器频宽. 那如果OP-AMP的BW是3MHZ,
是否用这OP-AMP构成的放大器的频宽可以达到更宽,如4MHZ ? |
| [答：Mariah] |
I don"t think using the negative feedback can make the bandwidth of
the amplifier larger. |
[2006-2-28 11:18:06] |
| [问：pulan] |
请问有没有输入范围为0-10V的差分12BIT的AD |
| [答：Mariah] |
What is the sample rate you want? |
[2006-2-28 11:18:19] |
| [问：hzluoping] |
降低基准电压是否能提高分辨率 |
| [答：Haoran] |
不可以，ADC的分辨率一般都是相对于它规定的参考电压。 |
[2006-2-28 11:18:29] |
| [问：gsdiscover] |
我使用的AD620，设定的放大倍数为10倍，对于正输入信号，输入输出之间关系非常线形，效果很好，可是负向信号输入时，小信号（0.08V以下）时放大效果也很好，线形度也行，但是信号强度超过0.08V时,其输出就不再发生变化，始终是0.823V左右，好像是放大后的信号被斩波了,出现了失真，我的供电电压为+-12V，输出5脚REF接地了，请给出解决办法？？ |
| [答：Mariah] |
What is your input common mode voltage? |
[2006-2-28 11:19:28] |
| [问：ecnanjing_EBY7E] |
在做环保测量设备中,通常前端的信号多是pA级的,请问选用AD什么样的放大器最为适合? |
| [答：Troy] |
The AD8691 is an excellent amplifier for many applications. |
[2006-2-28 11:19:29] |
| [问：zcs_1] |
DA后面的抗混叠滤波器怎么设计效果会比较理想？ |
| [答：Jing] |
It"s depend on your application such as the Fc or BPF bandwidth and
settling time. You can use our web fliter design tools to select your
corresponding filter . |
[2006-2-28 11:20:26] |
| [问：cqz] |
我检测行程传感器,使用外部的线性滑动电阻,要求采样频率20K,分辨率12bit请问ADI有什么合适的解决方案?SPI接口的AD有么,此外运放与AD间的RC怎么选择,它好像除了减少外部噪声的扰动外也跟内部的开关采样保持电容有关.上述要求麻烦给我个ADI的解决方案,包括基准源.性价比高些的. |
| [答：Xiangquan] |
I"m not sure your exact application, but for 12 bit, 20ksps sampling
rate ADC, you can choose AD7920, which is a low cost ADC, doesn"t need
external reference; For the low pass filter design, the simple one order
RC filter is enough, which fc=1/(2*pi*R*C) |
[2006-2-28 11:20:29] |
| [问：sxfs1984] |
怎样解决数据采集或ADC中的电磁干扰问题？ |
| [答：Troy] |
The best way to solve electro-magnetic interference (EMI) is surrounding
the circuit with a metal shield. Keep all trace lengths short. Using
a ground plane will also help. Where possible, use differential
signals. Most ADCs today are differential input for this reason. |
[2006-2-28 11:21:46] |
| [问：life1313] |
Can you advise a device for me to replace
ADC DEVICE of TVP5150A which is TI product |
| [答：Wenshuai] |
ADV7181 or ADV7180. 您给出更详细的要求的话，我们可以给您选择更合适的产品。也可以联系800 810 1742 |
[2006-2-28 11:22:37] |
| [问：jiaguowei] |
ADC或DAC如何选择数字地和模拟地的共地点，以减少数字地对模拟地的影响？ |
| [答：Jing] |
You can seperate digital GND and analog GND if the digital noise is
large. You can also look ADC/DAC"s digital GND as analog GND if the digital
noise and current is very large . You can combine digital and analog GND
together in one point. How to select the point is key . You can select
the minimun digital current circul and analog circul and combine it here
together. Thanks! |
[2006-2-28 11:23:51] |
| [问：吉星] |
ADC产品给出的数据参数ENOB与实际误差多大 |
| [答：Mariah] |
The ENOB is exactly what we measured. It depends on your system design. |
[2006-2-28 11:24:08] |
| [问：cola] |
能否介绍几种ＡＤＩ对高精度ＡＤＣ进行测试的方法？其优劣又在哪里？谢谢！ |
| [答：Haoran] |
对静态参数，输入直流信号要保持高精度，然后你可以测出INL，DNL还可以得到柱状图。
对动态参数，输入交流信号要保持高精度，时钟也要多考虑，做FFT分析，可以得到SNR和ENOB。 |
[2006-2-28 11:24:29] |
| [问：dengyt] |
请问专家,您对放大器温度补偿方法有何见解? |
| [答：Troy] |
It is very difficult to compensate an amplifier for temperature drift. Each
amplifier is different. We suggest using a low-drift amplifier
for precision applications. For example: AD8628 or AD8661. |
[2006-2-28 11:24:59] |
| [问：yz_yjg] |
有没有可能用分压器或别的方法来获得低电压的电压基准源? |
| [答：Haoran] |
ADI 有很宽范围的输出电压，从1V到10V都有。 |
[2006-2-28 11:25:59] |
| [问：roboy] |
我选用的AD转换器是AD7457，这是一个差分输入的转换器，假设信号的驱动能力足够强，我是否可以直接把外部输入信号的信号地直接接到vin-，而信号接到vin+，从而不用差分运放？。 |
| [答：Jing] |
If the input signal is large enough , you can do this. But I still recommend
that you use a differential AMP that will promote CMRR and you can also
condition your input signal commond voltage to the middle of the ADC input
voltage and add some LPF to minimize noise. |
[2006-2-28 11:26:39] |
| [问：dengyt] |
放大器的输出短路保护能力如何?在设计上如何考虑过载能力? |
| [答：Troy] |
Most amplifiers have output short-circuit protection. This
prevents the amplifier from damaging itself if the output is shorted to
ground. Our engineers design special circuits to detect if
there is a lot of output current. The amplifier turns off its
output stage in such a condition. Output short-circuit protection
is quite reliable. |
[2006-2-28 11:27:33] |
| [问：wzj0713] |
我们现在有一个数字场强仪的设计，目前正在对信号的前级输入作调理，输入信号是一个检波二极管采到的大尺度电流信号，向询问如何将这一信号藕进我们的目标电路可以使小信号不被淹没在噪声里？ |
| [答：Xiangquan] |
Could you please send the circuit and your questions to china.support@analog.com?
thanks |
[2006-2-28 11:27:46] |
| [问：yanmings] |
高输入阻抗、低偏置电流的运放在使用时需要注意什么？调零电路是否必须？ |
| [答：Jing] |
This kind of AMP always interface with current inout signal and you
should also pay attentation to the voltage offset and BGP of the AMP.
If you want to get better performance, you should add selt calibration
circuit to minimize the Ibias both in software of in hardware. Thanks! |
[2006-2-28 11:28:54] |
| [问：luckywin] |
差动放大器和差分放大器什么区别?差分放大器是用来干什么的,哪里有它的基本原理 |
| [答：Rui] |
差动放大器，Difference amplifer
可以在很高的共模电压的差分信号中，提取出差分信号。传递函数为 Vout=(V+IN)-(V-IN)
差分放大器 Differential amplifer
指输入/输入均为差分信号的放大器。增益由外接电阻设置
对于差动放大器，请参考AD629数据手册。对于差分放大器，请参考AD831*系列 |
[2006-2-28 11:29:12] |
| [问：jlwg] |
我在做称重系统时，电桥传感器需要10v的激励电压，我的做法是把ad7710自带的2.5v电压源作为标准电压源,并且将其接到运放op07的输入上，经放大成10v后再接到传感器上作为传感器的激励源。请问这样使用可不可以？对转换精度有无不良影响？ |
| [答：Mariah] |
You can use OP07 to generate the 10V excitation voltage of the bridge.
But you should think about the error which OP07 would bring, for example,
temp drift. Also the current driving capacility of OP07 should be considered.
If the output current of OP07 is not enough, you have to use a transistor
to dirve. |
[2006-2-28 11:31:02] |
| [问：xurn] |
请问有没有２．５Ｖ的带恒温的基准源？
有没有１８位以上的双极性输入、１００Ｋ以上的转换速率的ＡＤＣ芯片？
达到１８位以上的精度，双极性输入转差分如何实现？ |
| [答：Haoran] |
ADR431 is 2.5V output reference.
until now, we have no bipolar input 18bit ADC, but you can use bipolar
amplifier to attenuate signal to 0~5V, then use 18bit ADC. you can find
schematic in this presentation, which can be download in ADI website. |
[2006-2-28 11:31:17] |
| [问：jnfxt95] |
我用过AD7730信号调理器，用于衡器设计，性能指标非常好（特别是失调温度漂移很小，比AD7710好很多）。但AD7730是1998年的产品，价格有些贵。ADI近几年有没有推出用于衡器的新产品？ |
| [答：Mariah] |
AD7799 is the new product with high precision and highly recommended
to use in weigh scale design. |
[2006-2-28 11:31:49] |
| [问：yanmings] |
在弱信号放大器中，如何降低电源引起的噪声？ |
| [答：Jing] |
For small signal, You should select low Voltage offset and I bias AMP
such as AD8528,AD8555 etc. If the power supply is the major noise source,
I suggest you select a linear voltage source instead of switching power
supply. You can also filter the power supply using Pi filter and de-coupler
capacitor is very inportant, please select the low ESR capacitor in your
application and ensure the voltage ripple less than 1/10 of your signal. |
[2006-2-28 11:32:27] |
| [问：hzluoping] |
纳伏级直流信号放大是的增益带宽积如何计算 |
| [答：Rui] |
直流信号放大的时候不需要考虑增益带宽积的限制。
增益带宽积为信号放大倍数乘以信号频率。 |
[2006-2-28 11:33:22] |
| [问：dengyt] |
如何减少差分放大器的输入信号干扰? |
| [答：Haoran] |
it is hard to understand you question. you can contact 800-810-1742
for detail explaination. |
[2006-2-28 11:33:37] |
| [问：石林艳] |
时钟的选择用正弦波还是方波比较好？ |
| [答：Mariah] |
Can you give the specific application? It would be different in different
applications. |
[2006-2-28 11:33:43] |
| [问：engronger] |
放大器有时会出现自激和来自外部的干扰,如何避免? |
| [答：Troy] |
If you are refering to electro-magnetic interference (EMI), the best
way to avoid it is to enclose the circuit in a metal shield or box. Keep
all signal trace lengths short and use a ground plane if possible. Transmit
signals differentially to reduce any noise the traces pick up between
the amplifier and the ADC. |
[2006-2-28 11:33:43] |
| [问：xiexinpo] |
请问：在ADI的ADC Demo board 中有的模拟地和数字地用一只Ferrite
Bead 相连，而有的则直接相连，这两种方法区别又多大？那种更好些？谢谢！ |
| [答：Jing] |
I think a Ferriet Bead should be better to monimize the interter between
digital GND and analog GND. |
[2006-2-28 11:34:07] |
| [问：253760] |
我用AD872做间隔性数据采集，需要AD采集时才给时钟信号到AD872的时钟端，比如连续给1K个5Mhz时钟脉冲，前30个脉冲采集的结果总是不对，可能是什么原因? |
| [答：Xiangquan] |
you can try to keep the ADC continuously, it may be the ADC need time
to set up |
[2006-2-28 11:34:35] |
| [问：hznetwork] |
能否提供相关的技术资料以及设计案例 |
| [答：Rui] |
请问您需要相关什么的技术资料？如果需要更详细的帮助，请打800-810-1742，或者发邮件到china.support@analog.com寻求帮助 |
[2006-2-28 11:35:09] |
| [问：pulan] |
请推荐几款电表计量芯片。介绍一下 |
| [答：Jing] |
single phase:ADE7751/3/5
three phase : ADE7752/4/8
anti-theft: ADE7751/ADE7761 |
[2006-2-28 11:35:10] |
| [问：ypqecum] |
如何对电压基准源的温漂进行补偿? |
| [答：Troy] |
It is very difficult. Each part is different. We
recommend using a low drift amplifier or low drift amplifier for precision
applications. |
[2006-2-28 11:35:15] |
| [问：leontree] |
选择AD7789和779X时，能选择的最适当的参考基准源是哪几款 |
| [答：Mariah] |
ADR43x, AD780. You can use the reference wizard tool recommended in
the presentation to select the exact part which can meet all of your specific
requirement. |
[2006-2-28 11:35:17] |
| [问：pulan] |
AD输入前端是0-10V的信号，采用电阻分压的方式会对精度有何影响？专家有什么好的建议？ |
| [答：Troy] |
The voltage will be as accurate as the tolerance of the resistors. 1%
resistors will result in 1% voltage accuracy. |
[2006-2-28 11:37:01] |
| [问：pulan] |
现在的AD芯片对静电要求高吗？还有焊接这些是否会对AD造成致命伤害？ |
| [答：Xiangquan] |
almost all our parts have ESD protection in internal structure, soldering
commonly can not destroy the parts, but we highly recommend you power
off the soldering equipment during soldering |
[2006-2-28 11:37:03] |
| [问：roboy] |
ADI有没有能对pA级弱电流进行放大的器件？谢谢！ |
| [答：Haoran] |
AD8605/6/8 are good recommendation to you. |
[2006-2-28 11:37:11] |
| [问：caitouc] |
24位ADC需要什么样精度的基准电压源? |
| [答：Mariah] |
The most concern is the temperature drift and noise performance. |
[2006-2-28 11:38:05] |
| [问：shandong] |
请推荐几款高精度高速度的ADC芯片? |
| [答：Mariah] |
Would you please give the specification in details. |
[2006-2-28 11:38:38] |
| [问：ypqecum] |
如何消除EMI对基准电压源的输出噪音的影响? |
| [答：Troy] |
We recommend keeping the circuit inside a metal shield or box. Use
a low noise ground plane underneath the voltage reference. Use
a 0.1uF ceramic capacitor on both the input and output pins of the voltage
reference. You can add an additional 1nF capacitor in parallel
- smaller capacitors are better for reducing higher frequency noise. |
[2006-2-28 11:39:27] |
| [问：mayongtao] |
请问ad6644用什么放大器来驱动？ |
| [答：Jing] |
You can use AD8138 to drive it. Thanks! |
[2006-2-28 11:40:20] |
| [问：gsdiscover] |
如果一个测试系统的传感器输出电压范围为0-0.5v,精度为0.5mv,采用12位A/D转换器,应该选用的放大器增益为多少? |
| [答：Jing] |
If the input range of the ADV is 0--Vref, you can select a gain of 5
and Rail to rail amp to drive it such as AD8027 |
[2006-2-28 11:41:54] |
| [问：kivin_G] |
电压基准源流出和吸入电流的能力要留有多大的富余量? |
| [答：Troy] |
Very little. Most references require less than 1mA of supply
current. Refer to the datasheet for supply current specs. |
[2006-2-28 11:42:27] |
| [问：shandong] |
对于高速的ADC在布PCB板时,如何降低噪声,保证良好的精度. |
| [答：Mariah] |
You can send an email to china.support@analog. Then we can send the
application note talking about the details of high speed circuit layout. |
[2006-2-28 11:43:04] |
| [问：boclandc] |
现在我选用AD7655,输入信号差分信号,现在我选用AD620做驱动AD7655,是否合理,有没有更优的方案?谢谢!! |
| [答：Haoran] |
AD8221 is better one that can be replace AD620. |
[2006-2-28 11:44:37] |
| [问：kivin_G] |
在并联电压基准源时,需要考虑的因素有那些?能否推荐一些适合并联的电压基准源产品型号? |
| [答：Troy] |
We do not offer any combined voltage references. I don"t
know of any disadvantage to offering a combined reference. We
just haven"t offered one before. |
[2006-2-28 11:44:39] |
| [问：callhxw] |
使用外部基准源时，推荐为1.25V，而使用时采用1.2V，其他参数相同。请问能否达到要求？软件处理如何？ |
| [答：Mariah] |
First, you need to check whether the converter can accept 1.2V voltage
input. In your software, you also need to change the full scale point. |
[2006-2-28 11:44:50] |
| [问：msshen2003] |
选择精密ADC器件的原则是什么？ |
| [答：Mariah] |
Offset, noise, linearity and etc. |
[2006-2-28 11:45:47] |
| [问：engronger] |
运算放大器在使用的时候会有零漂的现象,请问调整零漂有什么好的办法? |
| [答：Troy] |
Use an auto-zero amplifier. AD8628 is an excellent choice. |
[2006-2-28 11:46:02] |
| [问：石林艳] |
AD6644基准参考源的输入电流有要求吗？ |
| [答：Jing] |
No special requirement, there is a BUF in our AD6644 that will promote
the deiven ability . |
[2006-2-28 11:46:07] |
| [问：woodxp] |
直流信号和交流信号的采集中分别需要根据哪些参数来选择合适型号的ADC如在高精度的低频信号测量中和图像采集需要怎么考虑？如何计算和测量实际电路中ADc的精度？ADc的精度和分辨率有何关系？在不考虑成本的情况下是不是量化位数越高越好？ |
| [答：Xiangquan] |
For ADC selection, mainly according the signal BW and your precision
requirements, for low speed signals, you can select sigma-delta ADCs if
the precision requirments are high, for video applications, we have video
ADCs and video decorders like ADV7180; For ADC precision measurements,
you can measure the peak to peak resolution of your system, the ADC bits
don"t equal precision, you can send a email to china.support@analog.com
for these concepts |
[2006-2-28 11:46:28] |
| [问：gsdiscover] |
我想问一下有什么方法能提高AD的动态范围 |
| [答：Jing] |
No better solution. One special ADC has it"s fixed maximum dynamic range
according to it"s specifaciton and datasheet. Thanks! |
[2006-2-28 11:47:59] |
| [问：yuke] |
你们哪的A/D可以低电压工作吗.耗电怎么样,有没有像MSP430的低功耗啊,可不可以给我几块A/D啊,我现在正想应用于张力控制,与温度采样.(:成功的话量大. |
| [答：Xiangquan] |
I"m not sure the voltage you require, some of our ADCs can work under
very low voltage, like AD7466, which can work under 1.6v power supply,
if you want to measure pressure and temperature, you can try AD7799, which
is a low power dissipation part; for sample application, pleas visit www.analog.com
for free sample request |
[2006-2-28 11:49:27] |
| [问：luckywin] |
请教,我要用运放设计一个射极跟随器,作为隔离电路，但要保证需要的中心频率21MHz，带宽4MHz的信号不被滤掉，请问用什么放大器比较好啊 |
| [答：Jing] |
You can use our Analog filter Wizard to for a BPF such as AD8027,AD8221
etc |
[2006-2-28 11:50:30] |
| [问：吉星] |
AD8067能否响应上升时间１０的钟形脉冲．若不能请推荐一个型号． |
| [答：Troy] |
The AD8067 rise time is close to 10ns and has a slew rate of 650V/us. You
should examine the AD8099 amplifier as well. Refer to the ADI
website at www.analog.com. |
[2006-2-28 11:50:45] |
| [问：yanmings] |
请问在ADC前级的放大器放大线性度不好时应如何进行调节? |
| [答：Xiangquan] |
You"d better select a right amplifer, as it"s hard to compensate |
[2006-2-28 11:50:56] |
| [问：honghai_zhu] |
基准电压源 有哪些值得关注的指标? |
| [答：Jing] |
Initial accuracy, reference voltage and temperature drift is important. |
[2006-2-28 11:51:09] |
| [问：hanxin] |
在选择前端运放的时候,有个参数叫"摆率",什么样的系统需要什么样的摆率哪?比如AD7865前端使用模拟开关,在电力系统应用需要选择运放的话,一般需要什么样的摆率的运放? |
| [答：Mariah] |
The slew rate depends on the signal frequency and amplitude. |
[2006-2-28 11:52:08] |
| [问：jessiesong] |
what"s the most important parameter in choosing
reference for ADC? |
| [答：Troy] |
It depends. Initial accuracy is usually important. So
is drift over temperature. 16+ bit applications may require
low noise. Portable applications need low supply current.
I find to many customers, the most important parameter is price! |
[2006-2-28 11:52:13] |
| [问：253760] |
我需要ADC间隙性工作，因此也间隙性给时钟，需要采集时才给时钟，这样是否有利于减少功耗，但这样会带来什么问题 |
| [答：Jing] |
You can do that. But please pay attentation to the clock jitter and
settling time . You should ensure the clock is stable for ADC,
then you can sample the input signal. By the way, fast switching should
also result some noise for your system. Thanks! |
[2006-2-28 11:53:09] |
| [问：zhouyl] |
请问我用10bit的ADC芯片需要高精度的参考电源吗？ |
| [答：Mariah] |
You should calculate your system precision requirement and then select
the suitable reference. |
[2006-2-28 11:53:21] |
| [问：吉星] |
能否推荐高阻抗，低输入电容，低噪声的放大器． |
| [答：Troy] |
I recommend using resistors with less than 200 ohms. Larger
resistors contribute more noise. Amplifiers with less than
12nV/root(Hz) noise are considered low noise. There are many
low priced low noise amplifiers you can buy, such as the AD8691 and AD8667. |
[2006-2-28 11:55:36] |
| [问：callhxw] |
请再加上ADC数据输出稳定数据与分辨率及精度之间的定义区别？ |
| [答：Rui] |
ADC的分辨率是指在不丢码的情况下ADC能达到的最高的Bit数
ADC的精度是指ADC的INL和DNL的误差。 |
[2006-2-28 11:56:03] |
| [问：cola] |
请问：基准电压源对ＡＤＣ的精度的影响具体表现在哪里？ |
| [答：Troy] |
The higher number of bits in the ADC, the greater the accuracy must
be from the voltage reference. |
[2006-2-28 11:56:28] |
| [问：ecnanjing_EBY7E] |
在微信号放大电路中,布线、印刷电路板的材质、焊接点、信号接入对整体性能的影响往往超过了放大器件本身的影响，请问专家对以上影响，特别是部线有何高见？ |
| [答：Mariah] |
You can send an email to china.support, then we can send some techinical
material on the PCB layout for high precision circuit. |
[2006-2-28 11:57:18] |
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