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一、密勒定理可用于双端输出差动放大电路带负载情况下电压放大倍数的分析。图1为双端输出差动放大电路的一部分。带负载时的电压放大倍数计算公式为对于为什么取1/2R_ L的理由,大多数教科书差不多都是这样叙述的:“因为输入差动信号时,C_1和C_2点的电位向相反的方向变化。一边增量为正,另一边增量为负,并且大小相等,可见负载电阻R_L中点是交流地电位,所以在差动输入的半边等效电路中,负载电阻是1/2R_L。”这样说固然不错,但若用密勒定理证明则更为严格一些。
A, Miller’s theorem can be used for double-ended output differential amplifier circuit with load magnification analysis. Figure 1 shows a part of the double-ended output differential amplifier. The voltage magnification at load is calculated as the reason why 1 / 2R_ L is taken. Most textbooks describe this almost as follows: "Since the differential signals are input, the potentials at points C_1 and C_2 change in opposite directions. The increment is positive and the other increment is negative, and the size is equal. It can be seen that the middle point of the load resistor R_L is the AC ground potential, so the load resistance is 1 / 2R_L in the half-equivalent circuit of the differential input. Although not bad, Miller’s theorem is more restrictive.