who can help me explain this problem!

[yin83]

Recently,I have done a simple circuit design and simulation , what i only can cumpute is the W\L, but i don't know how to decide the MOSFET's channel length.
as i know ,the MOSFETs with different channel length ,although have the same W\L ,have different performance ,please help me!
thanks

Added after 1 hours 16 minutes:

why nobody replys me ?
you can display your explaination whatever it is right or wrong,there is no matter!
thanks all

 

[benchen]

I think if there is no match problem or channel modulation cosideration, use the smallest L.

 

[yin83]

this is the W\L in the circuit,184um\9um,184um\6um,36um\10um,145um\12um,
so i think there is no relationship with match problem or channel length modulation for considering this problem,because all the channel length is big
can somebody explain this?
thanks for every one replying me !

 

[nassim_el85]

It may relate to the ro of transistors. For example, if the architecture is an amplifier, the lengths of the transistors are usually set to achieve specific ro and therefore gain.

 

[analog_prodigy]

if u put different channel lengths, there will be definetly matching problems in layout.
though it works in simulations, there will be defenetly a problem in real envionment

 

[yin83]

all the matched transistors have the same length ,so i think it is not the answer of the problem ,this circuit is in the book of CMOS Analog Circuit Design,the Second Edition.so i think all the channel length in this circuit is right .It should be selected like it show.
this circuit with low ouput resistance can be the cushion output level of the op-amp ,and its gain is unity.so i don't think it has relationship with amp gain through evaluating the bigger channel length.
My english is poor ,if i havn't express it right ,please ask me again .
thanks!

 

[jeffsky520]

help yourself to choose channel length if nothing considered.