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大家好，希望有人能帮上忙，我用16F1779做一些模拟的事情，我用的是所有的OPA模块，它仍然没有“干净”我的信号。所以我使用了一个比较器的输出，它有点噪音，把RC LO通行证放在上面，得到了一个不错的信号，我认为另一个比较器可以。当我把这个连接到比较器输入时，出现了一个17KHz锯齿状的噪声位！如果我引用比较器的+输入到GND，噪音就会消失（DAC 1是+输入）。有人有这样的问题吗？似乎噪音来自DAC？或者是比较器模块？（一个比较器在喂另一个？干杯杰夫
以上来自于百度翻译 以下为原文 Hi all, Hope someone can help, I'm using a 16f1779 for some analog stuff, I'm using all the opa modules, which still didn't 'clean' my signal enough. So I used the output from a comparator which was a bit noisey put a rc lo pass on it and got a nice signal which I thought another comparator could make digital. When I connect this to a comparator input a ~17khz saw tooth bit of noise appeared! If I reference the + input of the comparator to gnd the noise goes away (DAC 1 was + input). Anyone had problems like this? It seems the noise is coming from the DAC? Or could it be the comparator module? (One comparator is 'feeding' another?! Cheers Geoff 
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12个回答
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通常，OpAmps的级联会引起自振荡问题：增益太高，或者相位旋转（由于电容器等）…
以上来自于百度翻译 以下为原文 Usually, yep, a cascade of OpAmps can cause self-oscillating issues: too high the gain, or phase-revolving (due to capacitors etc)... |
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谢谢，这个信号在连接到一个ANOLG输入的范围内看起来很好，只有当它连接到比较器时，我才看到噪音。有什么办法解决它吗？欢呼杰夫
以上来自于百度翻译 以下为原文 Thanks, the signal looks fine on the scope even connected to a anolog input, its only when connected to the comparator I see the noise. Any idea how to resolve it? Cheers Geoff |
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我在输入上有迟滞，这是我唯一没有尝试改变的东西！这会引起我的注意吗？当我回来的时候，我会尝试改变它。谢谢杰夫。
以上来自于百度翻译 以下为原文 I have got hysteresis on the input at the moment, that's the only thing I haven't tried changing! Could that cause what I'm seeing? Am away from it at the moment will try changing it when I get back. Thanks Geoff |
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可能你在DAC中得到一些电源馈通？
以上来自于百度翻译 以下为原文 Possibly you are getting some power supply feedthrough in the DAC? |
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你用什么来做DAC参考？VDD或FVR？如果您正在使用FVR，尝试将VREF+引脚（如电池）上的非常稳定的电压改变为快速测试。您还可以尝试在睡眠中运行模拟测试，以隔离任何杂散的数字干扰。
以上来自于百度翻译 以下为原文 What are you using for the DAC reference? Vdd or FVR? If you are using the FVR try changing to a very stable voltage on the Vref+ pin (such as a battery) as a quick test. You can also try running the analog tests in sleep to isolate any stray digital interference. |
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我用VDD作为DAC电源，不知我是否需要改进我的过滤器？它只是一个电阻器和电容器。以前的版本与需要额外的比较器一起工作，这是一个带有外部运算放大器的16F1827，我从数据表中看到，1872的HYS是65 MV，典型的是75个最大的1779×4MV。？！我以为他们是一样的？我也认为我需要更多，所以可能需要在外部添加。我看不到电源上的噪音。谢谢杰夫。
以上来自于百度翻译 以下为原文 I'm using vdd as the DAC supply, I wonder if I need to improve my filter? It is just a resistor and capacitor. A previous version worked with out needing this extra comparator, this was a 16f1827 with external op amps, I see from the data sheet the 1872 has 65mv of hys and the 1779 45mv typical 75 max??! I had assumed they would be the same ? I also think I need more than that so may need to add it externally. I can't see noise on the supply. Thanks Geoff |
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你能解释一下这段话吗？第二个比较器是由另一个比较器或运算放大器喂的吗？
以上来自于百度翻译 以下为原文 Can you explain this paragraph? Is the second comparator being fed by a another comparator or an op amp like I first thought when I read your initial post? |
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没错，有一些短的变化我想摆脱，低通就行了，但是我不能用那个信号驱动下一个比较器。我试着改变RC的值，如果它是输入阻抗问题。假设我什么都不知道，你不会错的，我想我很幸运。1827个比较器，我需要~65毫伏的HYS。谢谢杰夫
以上来自于百度翻译 以下为原文 That's right, there were some short changes I wanted to get rid of, the low pass did that OK but I can't drive the next comparator with that signal. I've tried changing the values of the rc in case it was a input impedance issue. Assume I know nothing and you won't be far wrong, I think I was lucky with the 1827 comparator, I need ~65mv of hys. Thanks Geoff |
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我不确定我理解你为什么级联2个比较器。你确定第一个不应该是运算放大器吗？
以上来自于百度翻译 以下为原文 I'm not sure I understand why you are cascading 2 comparators. Are you sure that the first one shouldn't be a op amp? |
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它可能应该是，我试图使我的电路与什么板上的1779，所以所有运算放大器使用。我想这可能是个办法吗？我以前的电路与4个外部运算放大器，所以我希望这将……谢谢杰夫
以上来自于百度翻译 以下为原文 It probably should, I'm trying to make my circuit with what's on board the 1779, so all the op amps are used. I thought this maybe a way round that? My previous circuit works with 4 external op amps so I was hoping this would...... Thanks Geoff |
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谢谢你的评论，你让我走上了正确的道路！我重新访问运算放大器部分并提高了前面两个运算放大器的增益，这已经给出了足够的分离，以便从比较器获得良好的输出。
以上来自于百度翻译 以下为原文 Thanks for the comments, you have sent me down the right path! I revisited the op amp section and upped the gain on both of the preceding op amps, this has given enough separation to get a good output from the comparator. Cheers Geoff |
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