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Current source Loads.

Hi,

Recently I came across a topic"Common source stage with current source as load" while going through single stage amplifiers design using MOS. I came across a statement that in Common Source stage, "PMOS is more preferred to used as current source load than NMOS". I would be grateful, if someone please explain me the actual reason of that statement. Kindly mention the reference link if any. 

Thanks in advance!!!

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  • This not the proper forum to answer this question in detail. But the short answer comes from an observation by analog transistor level IC designers that in most IC processes the output resistance i.e. Ro, source to drain resistance in saturation of PMOS is higher than NMOS.

    Why is that generally the case you ask? A full answer is beyond what could be discussed here but again the short answer is that MOS transistors are minority carrier devices and the holes (PMOS) have different properties than electrons (NMOS).

    I would suggest you read a solid state physics text book for a more detailed explanation ( or take a course in .solid state physics ).

    Doug

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  • This not the proper forum to answer this question in detail. But the short answer comes from an observation by analog transistor level IC designers that in most IC processes the output resistance i.e. Ro, source to drain resistance in saturation of PMOS is higher than NMOS.

    Why is that generally the case you ask? A full answer is beyond what could be discussed here but again the short answer is that MOS transistors are minority carrier devices and the holes (PMOS) have different properties than electrons (NMOS).

    I would suggest you read a solid state physics text book for a more detailed explanation ( or take a course in .solid state physics ).

    Doug

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