can i set the current mirror ratio to 20:1

Status
Not open for further replies.
F

foreverloves

Member level 1
Joined
Mar 23, 2006
Messages
38
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,620
If i need a steady but not an accuracy current, can i set the current mirror ratio to
20:1?

for example, I have a current source of 200uA, but I need a current of 10uA(10.5, or 9.6 are also ok, accuracy is not required, I need it to be steady), can i
set the current mirror ratio to 20:1?

can there be any other problems ?
 

as far as i know since accuracy is not required then there is no problem
 

With CMOS you should be ok scaling down currents. Scaling up can be an issue because any input noisae will alsi scale up.
 

definitely you can. In fact, with this ratio you can even scale up, with proper care in layout, quite accurately.
 

In terms of layout (or reliability) issue, I would recommend 200uA to 50uA, then 50uA to 10uA.
 

sure u can, but assure current mirror matching in the layout
 

Hi wpchan05
why u recommend 200uA to 50uA, then 50uA to 10uA in term of layout.
better matching can be got with low current ratio ?
 

i am using ratio of 100!!! ,, accuracy idnt concern me much as long as i am within the specified limits,,,as in my application i depend on the current gain ,,i.e. as it is bigger it is better,,,,if anyone can tell me the problem of that it would be great,,,
 

davidwong said:
Hi wpchan05
why u recommend 200uA to 50uA, then 50uA to 10uA in term of layout.
better matching can be got with low current ratio ?
Click to expand...

I always limit all my current mirror ratio up to 5 or down to 1/5 so as to reduce parameters variation of the transistors within a chip. Although the first author mentioned that a high precision current gain is not required in his design, I have no confidence on expecting a current mirror with a ratio of 20:1 can achieve 95% accuracy, from a statistical point of view.
 


well , i f i want a certain current , then can i make sweep to get it regardless the ratio of current mirror ? is this will create a problem??,,
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…