ADC选择最合适的基准电压源和放大器

如何为您的ADC选择最合适的基准电压源和放大器

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 /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@, 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？