How to layout cascode opamp ?

[holddreams]

How to layout the cascode opamp on RAZAVI'S book ,figure 9.48?

Any suggestion?
In figure 9.48,
(1) put the M1,M2 ,M1P,M2P in the middle of M9 ,M10 ,M3, M4, M5, M6, M7, M8
(2)put the M1, M2 ,M1P,M2P just in the left or right of M3 to M10
which one will be better?

 

[sunking]

here is a lecture for you reference

 

[tony_wu_ad]

I have just see the figure of 9.48

I think it is not better to put the M1,M2 ,M1P,M2P in the middle of M9 ,M10 ,M3, M4, M5, M6, M7, M8 .I think it will be increase mismatch of M9 M10

 

[holddreams]

Thanks a lot , I will try.

 

[holddreams]

hi,
sunking,

which size of M1,M2 you use in design a cascode opamp?
I mean ,when layout the cascode opamp circuit,
if the fingers of M1,M2 is large,then the w/l will be too small.
Which size of w/l will be suitable?2.5 /1 or else.

thanks.

 

[disney]

I will go for option 2, which is more practical and reduces lot of inter layer capacitances...

 

[holddreams]

I have read the lecture sent by sunking,
The lecture introduces a way to draw cascode opamp layout of same L.
Here I have a question:
How to draw the layout when the Length of all MOS transistors are not same?
For a cascode opamp ,if increase the Length of M5,M6,the gain will increase too.

 

[sunking]

I think it is not the same L, but the same W.
And the lecture is just a method.
By the way, you can split the W for the same finger

 

[holddreams]

yes ,the W is the same,
but when the length is different, how to place?
The total length (include the dran and source length ) of each of the stacked mos transistors should be equal?

 

[sunking]

it is need not.
in fact, the method of lecture is just for you reference.

 

[tony_wu_ad]

I think it is not the same L, but the same W.
And the lecture is just a method.
By the way, you can split the W for the same finger

not the same L, but the same W?

I have a question: if it is not the same L, but the same W, the Leff of MOS will be not same to eachother.

So , I think it is the same L ,not the same W

 

[starcoming]

Agree to the lastest answer. It is the same L for the same channel length effect.

 

[holddreams]

according to the pdf uploaded by sunking ,the method is to draw the layout ----

(1)same width of the fingers in the same stack,possibly different length.

(2)use(almost)the same number of finger per stack.

Maybe there will other good way.