[问答]

PIC32MZ差分ADC需要内部上拉电阻

问答对人有帮助，内容完整，我也想知道答案 0 大家好。我希望有人能给我解释一下我在PIC32 MZ遇到的一个奇怪的行为。我设计了一个超声波板，通过一个电容器给差分信号的每一条腿供电，然后在模拟前端生产商推荐的PIC32 MZ2048 EFH144上提供模拟引脚。PIC固件配置引脚是差分I类模拟输入。它也在100US突发中采样非常快（10 MSPS），使用DMA将样本发送到缓冲器。如果我设置的引脚，你通常会为ADC（没有上拉电阻，没有ODC），它不起作用。但是，如果我设置了引脚，使内部拉电阻，它工作得很漂亮，并在100US窗口采样干净的声波。我很高兴，我找到了一个解决方案，但这对我没有任何意义。文档说明在配置为ADC的引脚上禁用上拉和下拉电阻器。如果没有禁用PUs，那么这不会破坏信号吗？这种行为在许多专业组装的PCB上是相同的。我到处找不到任何信息，勘误表里什么也没有。如果有人对发生的事情有任何想法，我很感兴趣。谢谢，安迪。以上来自于百度翻译以下为原文 Hello everyone. I'm hoping someone can explain to me a strange behavior I've encountered with the PIC32MZ. I designed an ultrasound board that feeds each leg of a differential signal through a capacitor, then to analog pins on a PIC32MZ2048EFH144, as recommended by the analog front end manufacturer. The PIC firmware configures the pins to be differential class I analog input. It's also sampling very fast (10 MSPS) in a 100us burst, using DMA to send the samples to a buffer. If I set the pins how you normally would for ADC (no pull up resistors, no ODC), it doesn't work. If however, I set the pins to enable the internal pull up resistors, it works beautifully, and samples a clean sound wave over the 100us window. I'm happy that I've found a solution, however this doesn't make any sense to me. The documentation states that pull up and pull down resistors are disabled on pins that are configured for ADC. If the PURs weren't disabled, wouldn't that corrupt the signal? This behavior is identical across many PCBs that were professionally assembled. I couldn't find any information anywhere on this, and there isn't anything in the errata. I am very interested if anyone has any ideas as to what is happening. Thanks, -Andy 0
2018-10-23 15:46:37　　评论淘帖0 邀请回答您可以邀请以下用户，快速回答问题 × qun333 该类别下有 57 个回答。邀请回答 caoguiqun 该类别下有 56 个回答。邀请回答技术发广告该类别下有 56 个回答。邀请回答 psw30 该类别下有 44 个回答。邀请回答伊丹姿子该类别下有 41 个回答。邀请回答 uwufwjrw 该类别下有 39 个回答。邀请回答 hetao1111 该类别下有 38 个回答。邀请回答 lc123617 该类别下有 35 个回答。邀请回答欧阳大大该类别下有 32 个回答。邀请回答作死不止该类别下有 31 个回答。邀请回答 asd010 该类别下有 31 个回答。邀请回答 60user92 该类别下有 29 个回答。邀请回答 wy8719 该类别下有 29 个回答。邀请回答嘻嘻爱哈哈该类别下有 28 个回答。邀请回答 haikitty 该类别下有 28 个回答。邀请回答 ju978779 该类别下有 28 个回答。邀请回答 xiuzhen122 该类别下有 27 个回答。邀请回答 pol666 该类别下有 27 个回答。邀请回答 ueywyrsdfs 该类别下有 26 个回答。邀请回答 lhly23 该类别下有 25 个回答。邀请回答举报李可熠相关推荐 • PIC32MZ可以同时上拉和输入捕捉吗？ 1348 • 怎么选择PIC32MZ2048EFH144的触摸驱动器 1692 • PIC32MZ(EC) Board + PIC32MZ2048EFH144出现错误 2472 • 为什么pic32mz gpio速度需要50ns？ 778 • PIC32MZ谐波动态驱动程序入门 651 • pic32mz的stdlib在哪里？ 1474 • Harmony PIC32MZ扫描所有ADC，但缺少Class1 AN0-AN4 1686 • PIC32MZ Uart不能发送TX到终端 2716 • 为什么PIC32MZ不支持密钥存储？ 835 • PIC32MZ扫描的ADCHS串扰采样时间问题 1051 2个回答

答案对人有帮助，有参考价值 0 HI，ADC输入在器件内部充电一个采样电容，ADC在转换期间具有稳定的电压。当转换完成时，采样电容在连接到ADC输入之前被放电，用于下一个样本的充电。如果有交流耦合输入信号，将有BIa。S网络需要将平均电压拉到有效范围内，如果没有偏置，输入电压可能被拉到有效范围以下。在这种情况下，内部WPU看起来可能提供偏置电流。应该使用直流模式的示波器来观察信号，并验证输入电平是否为I。n范围。迈西尔以上来自于百度翻译以下为原文 Hi, ADC inputs charge a sampling capacitor inside the device, for ADC to have a stable voltage during conversion. When conversion is completed, the sampling capacitor is discharged before connecting to ADC input for charging for the next sample. If there is AC coupled input signal, there will be a bias network needed to pull average voltage into valid range. If there is no bias, input voltage may be pulled down below valid range. In this case, it may seem that internal WPU provide bias current. You should apply a oscilloscope using DC mode to observe signals, and verify that input levels are within range. Mysil

2018-10-23 15:58:23 评论举报李铭鑫

答案对人有帮助，有参考价值 0 哇，这正是问题所在。我去掉了去耦电容，信号的每一个支路现在被偏置在1.5V。采样波可以在我们的软件中显示，现在看起来与外部范围的采样几乎相同。数据表非常混乱。谢谢你的小费！-安迪以上来自于百度翻译以下为原文 Wow, this is exactly what the problem was. I removed the decoupling capacitors and each leg of the signal is now biased at 1.5V. The sampled wave can be displayed in our software, and now looks nearly identical to sampling with an external scope. The datasheets are pretty confusing. Thanks for the tip! -Andy

2018-10-23 16:16:36 评论举报乔丽娜