Integrated Operational Amplifier

In China:

The $\infty$ 表示理想中的无限放大

In United States:

这里补一个概念：

电流为0时可以有电压（没电流时电压可能存在）
解释：电压一直有但没回路、没负载，电阻无穷大，电流为0
没有电压必然没有电流（有电流一定有电压）
解释：因为电流(电子)流动是因为有电压差

Inversed_Integrated_Operational_Amplifier (反向输入比例运算电路)

\begin{align*} &\because i_+ = 0 \text{ , } \therefore u_+ = 0 \\ \\ &\because u_+ = u_- \text{ , } \therefore u_- = 0 \\ \\ &\text{ } i_1 = \frac{u_i - u_-}{R_1} = \frac{u_i}{R_1} \text{ , } i_f = \frac{u_- - u_o}{R_f} = \frac{-u_o}{R_f} \\ \\ &\because u_- = 0 \text{ 无电压就无电流, } \therefore i_1 = i_f \\ \\ &\therefore u_o = -\frac{R_f}{R_1} u_i \end{align*}

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Inversed_Integrated_Operational_Amplifier (反向输入比例运算电路)

\begin{align*} &\because i_+ = 0 \text{ , } \therefore u_+ = 0 \\ \\ &\because u_+ = u_- \text{ , } \therefore u_- = 0 \\ \\ &\text{ } i_1 = \frac{u_i - u_-}{R_1} = \frac{u_i}{R_1} \text{ , } i_f = \frac{u_- - u_o}{R_f} = \frac{-u_o}{R_f} \\ \\ &\because u_- = 0 \text{ 无电压就无电流, } \therefore i_1 = i_f \\ \\ &\therefore u_o = -\frac{R_f}{R_1} u_i \end{align*}