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about layout of mirror

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lhlbluesky

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to mirror current exactly,the ratio of W/L of the mirrored and mirroring transistor should be exact,too;i want to ask ,for W/L=50/0.5 with finger number=10 (mirroring transistor)and W/L=10/0.5 with finger number=2 (mirrored transistor),how is the layout?if i use the technique of sharing source and drain,the parasitic cap may be different,and the ratio can be not exact;how to solve it.pls.
 

your ration is a little too large: 500/20
try unit element and cc techniques etc.
 

lhlbluesky said:
to mirror current exactly,the ratio of W/L of the mirrored and mirroring transistor should be exact,too;i want to ask ,for W/L=50/0.5 with finger number=10 (mirroring transistor)and W/L=10/0.5 with finger number=2 (mirrored transistor),how is the layout?if i use the technique of sharing source and drain,the parasitic cap may be different,and the ratio can be not exact;how to solve it.pls.

Usually the parasitic of Current mirror is not critical.
And is 50/0.5 is the total size?
if it is 500/0.5 and the other is 20/0.5, the ratio will be too large,
you'd better use the high swing cascode mirror.

And 0.5u length is too small for current mirror.
Beside, which circuit does the current mirror use?
 

Usually the parasitic of Current mirror is not critical.
And is 50/0.5 is the total size?
if it is 500/0.5 and the other is 20/0.5, the ratio will be too large,
you'd better use the high swing cascode mirror.

And 0.5u length is too small for current mirror.
Beside, which circuit does the current mirror use?[/quote]


I think 50/0.5 is the total size,If it is 500/0.5,the parameter would be M=10,but here it is nf=10,the finger width is 5/0.5
I have met the same poblem when designing a current mirror with chartered 0.13um process. When I used the 'w=10u ,M=5' ,total width is 50u, the current will be well matched,but when I use 'w=50u,nf=5',it has a great mismatch about 10%.
I think the layout is like 'w=50u,nf=5'.
I also want to kown,which one I shoud use,thanks
 

sgoat said:
I have met the same poblem when designing a current mirror with chartered 0.13um process. When I used the 'w=10u ,M=5' ,total width is 50u, the current will be well matched,but when I use 'w=50u,nf=5',it has a great mismatch about 10%.
I think the layout is like 'w=50u,nf=5'.
I also want to kown,which one I shoud use,thanks

I think for good matching of current mirrors they should have same W , finger no.s , & length .While varying the no. of units (M) to vary the mirroring ratio.
 

Hi
Using large values for w and l would result in better matching. The parasitic caps can restrict your BW not your matching.
 

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