与电压无关的基准

这个小弟从版图中提取出来的电路。以下是我个人理解。
本来是一个自举基准源，外面的两个pmos是为了对里面的两个pmos的分流，使里面的两个pmos的小信号输出阻抗变大，从而受电源变化的影响减小。
此电路没有启动电路?
二极管可以起稳压作用，但电阻怎么会是浮空的?是该接地 还是接电源?

望各位不吝赐教。

有没有提错啊?

If your circuit is right, then the open end of the resistor should be connected to an external adjustable voltage source or simply a certain fixed voltage.  In this case, the PMOS whose gate is connected to the resistor can function as a bias current source.  It can force the current through the PTAT current source.  After the PTAT current source goes into the normal stable point (not zero), the one whose drain connecting to the resistor will conduct.  And the drain voltage will go down to a level such that the bias current source and the bypass NMOS shut down.  The startup circuit is actually composed by 4 transistors.  The resistor provides a voltage drop when there is some current.  The diode is for ESD protection.  That is what I think.  Correct me if I am wrong.

Actually, a lot of PTAT current sources use single transistor+a big resistor as the startup circuit.  The advantage of this one, I think, is that it is controllable and better symmetry could be achieved.  Since the startup transistor will introduce systematic error to the PTAT current.

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