Both long-channel and cascode MOS transistors are used in VLSI design to increase output impedance of current sources (for instances : AE_Lecture8_PartB_Incremental Model of FET or Bias circuit design for low-voltage cascode transistors DOI: 10.1145/1150343.1150372).
Moreover, self-cascode MOS transistors can be definitely seen as a single long-channel MOS transistor (Self-cascode composite transistor Analog and Mixed-Signal Center - ELEN 607 ESS).
So, to improve the output impedance of a current sources, what are the pro/cons reasons to choose a longe-channel or a cascode MOS output transistor?
Adding to the colleagues above, I think the cascode current mirror configuration is basically outperforms the long channel transistors as the output transistor in the cascode is common gate transistor where the long channel transistor is still common source suffering from channel shortening due to the an increase in VDS. This effect is called Early effect. But it may have an area penalty against the cascode current mirror where a lower output resistance is acceptable for the current mirror.
Best wishes
I agree:
In between a single transistor and 2 cascoded transistors, the second solution provides better performances (but use more than 2 times space).
The question is more, whats the difference in the case of 2 cascoded transistors vs 1 transistor twice as long (long-channel)? ...using essentially the same surface area
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