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Design >> Analog Design >> High speed, high mirror ratio current mirror
https://designers-guide.org/forum/YaBB.pl?num=1211923481

Message started by jiesteve on May 27^th, 2008, 2:24pm

Title: High speed, high mirror ratio current mirror
Post by jiesteve on May 27^th, 2008, 2:24pm

I am trying to design a current mirror with a high mirroring ratio (1:12, input current=40uA, output=480uA). Do you think the topology attached could work? How should I size the source follower and current source? I need very fast settling time, ~10ns.

Title: Re: High speed, high mirror ratio current mirror
Post by weber8722 on Mar 17^th, 2009, 7:27am

Hi,

for good settling you need a frequency compensation. Use a series RC from input to Vdd, like 500fF + 10k.
Otherwise you get a large overshoot and big noise peaking too.

Bye Stephan

Title: Re: High speed, high mirror ratio current mirror
Post by rf-design on Mar 24^th, 2009, 10:39am

Very fast depending on your tech, Vdsat and Length.

A good guess is to have a sqrt(12) * input current on the mirror buffer.

Title: Re: High speed, high mirror ratio current mirror
Post by vivkr on Mar 25^th, 2009, 12:04am

AnalogDE wrote on May 27^th, 2008, 2:24pm:

I would also try to see if a Wilson current mirror could be used (headroom permitting). This is generally quite fast for high mirror ratios.

Regards,

Vivek