套筒式结构运放为什么很难使输入和输出短接

Generally, telescopic opamp Input CM range is too small to cover telescopic opamp Output Signal range (including CM+DM components)。Once output signal range exceed telescopic opamp Input CM range，the performance (eg. gain/bandwith) of telescopic opamp will degrade.
However, in casethat the input signal is a DC voltage level and within the Input CM range of telescopic opamp, the input and output terminals of telescopic opamp can be connected directlty to configure a non-inverting gain (=1) amplifier/buffer.

因为输入共模点的问题

这书上不是说的很明白吗

明白了，谢谢大家的解答

overlap of input and output range is little

学习了.