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虽然双极型运算放大器失调电压是固有的,但其量值要比场效应晶体管(FETS)低一个数量级,后者是由于它们的偏置电流低,所以广泛使用了。这篇报告将讨论双极型输入级的设计,当相等于场效应管的偏置电流时,它就要求保持一个低的失调电压和漂移。唯一的,对于高至125℃温度,偏置电流保持很小。 如(?)图1可以看出,这个设计利用一个按修正的达林顿连接的超增益晶体管。反偏晶体管Q_7为Q_1和Q_2提供相当地偏置电流,这个偏置电流可观地超过Q_3和Q_4的基极电流。实际上,这种偏置消除了复合晶体管连接的许多讨厌的特性。
Although bipolar op-amp offset voltages are inherent, they are orders of magnitude lower than field effect transistors (FETS), the latter of which are widely used due to their low bias current. This report will discuss the design of a bipolar input stage that requires a low offset voltage and drift when equal to the FET bias current. The only thing that happens is that the bias current remains low for temperatures as high as 125 ° C. As can be seen in Figure 1, this design utilizes a modified Darlington-connected super-gain transistor. Reverse-biased transistor Q_7 provides a relatively high bias current for Q_1 and Q_2. This bias current considerably exceeds the base current of Q_3 and Q_4. In fact, this offset eliminates many of the annoying features of a compound transistor connection.