Op-Amp Open Loop Gain

The high open loop gain leads to the voltage rule. 高开环增益导致电压规则

Practically, the gain is so high that the output will be driven to 实际上，增益非常高，使得输出会被驱动到 for any appreciable difference between 对于任何显著的差异之间 This is useful in the comparator. 这在比较器中很有用。 For practical applications other than the comparator, negative feedback is used to control the device gain. 在除比较器以外的实用应用中，负反馈用于控制设备的增益。

Negative Feedback

The use of negative feedback reduces the gain, but most other rationales favor its use. Part of the output signal is taken back to the input with a negative sign.

For an amplifer with negative feedback the gain becomes

The large open loop gain of an op-amp makes it possible to build amplifiers whose gain is determined by the feedback B and not by the gain of the amplifying element itself!

Rationale for Negative Feedback

Why would you feed back a negative signal from the output which cancels part of the input, reducing the gain? 为什么要把输出端的负反馈信号反馈回输入端，以抵消部分输入信号，从而降低增益？

Because:

• It helps to overcome distortion and nonlinearity.
  它有助于克服失真和非线性。
• It flattens frequency response or allows you to tailor it to a desired frequency response curve.
  它可以使频率响应趋于平坦，或者允许你根据所需的频率响应曲线进行调整。
• It makes properties predictable, less dependent on temperature, manufacturing differences or other internal properties of the active device.
  它使属性变得可预测，较少依赖于温度、制造差异或其他活性器件的内部属性。
• Circuit properties are dependent upon the external feedback network and are thus easily controlled by external circuit elements.
  电路特性取决于外部反馈网络，因此很容易通过外部电路元件进行控制。
• Circuit design can concentrate on function and not the details of operating point selection, biasing, and the other details characteristic of discrete transistor amplifier design.
  电路设计可以专注于功能，而不必考虑工作点选择、偏置以及其它特征于离散晶体管放大器设计的细节。