[2.1 数字地，模拟地，电源地的处理](2.1%E6%95%B0%E5%AD%97%E5%9C%B0%EF%BC%8C%E6%A8%A1%E6%8B%9F%E5%9C%B0%EF%BC%8C%E7%94%B5%E6%BA%90%E5%9C%B0%E7%9A%84%E5%A4%84%E7%90%86.md) [2.2 关于开漏输出和推挽输出](2.2%E5%85%B3%E4%BA%8E%E5%BC%80%E6%BC%8F%E8%BE%93%E5%87%BA%E5%92%8C%E6%8E%A8%E6%8C%BD%E8%BE%93%E5%87%BA.md) [2.3 信号调理电路](2.3%E4%BF%A1%E5%8F%B7%E8%B0%83%E7%90%86%E7%94%B5%E8%B7%AF.md) [2.4 运放使用的下拉电阻](2.4%E8%BF%90%E6%94%BE%E4%BD%BF%E7%94%A8%E7%9A%84%E4%B8%8B%E6%8B%89%E7%94%B5%E9%98%BB.md)