current mirror problem

[memsgg]

I have a 5 uA refference current, I need 200uA current by current mirror.

can I use one current mirror with very large w/l (>100:1) to get this 200 uA current? Is there any problem?

thanks a lot

 

[ieropsaltic]

Such an idea may work but with a very major disadvantage; the reference noise will be multiplied by the same ratio yielding to a very large noise at the output .So, if noise is not an issue for you, you can try this solution .

 

[ravet]

as i see, you want to mirror by ratio 40 times , so as mentioned above, reference noise will be multiplied by the same ratio !! , increasing the size decreases the flicker noise of the devices & also the current source becomes better as its output resistance increases ( when you increase the length of the device ) if the noise annoys you , then you will need to put low path filter between the reference and the mirrors, this LPF will not eleiminate the flicker noise of the devices as it is usually at low frequencies and you will need a very big cap to reach this frequencies, but you can decrease the flicker noise by increasing the devices size, and thus you have trade-off between: 1- filtering the reference noise 2- when adding the filter this will affect the start-up time of the circuit 3- area

enjoy ic design

 

[memsgg]

Such an idea may work but with a very major disadvantage; the reference noise will be multiplied by the same ratio yielding to a very large noise at the output .So, if noise is not an issue for you, you can try this solution .

Yes, noise is an issue for me, then what should i do? just reduce w/l?

 

[drabos]

rather increase

 

[wallycharlo]

you will desire a high overdrive for good matching,which would argue for large L ...