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Q&A

Comments on Is a BJT 3-transistor Wilson mirror faster than a simple mirror?

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Is a BJT 3-transistor Wilson mirror faster than a simple mirror?

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My question is trying to understand if there is an effect on the switching time, on both turn-on and turn-off, between the following configurations.

A mirror set up to switch a current, and there is switching on the input side of the mirror input (for other reasons), meaning the simple mirror's base voltage must ramp up and down from near zero each time. In this configuration, is there a speed benefit to the 3-transistor Wilson mirror? Talking about discrete components, ~1 MHz switch freq.

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General comments (4 comments)
General comments
Olin Lathrop‭ wrote about 3 years ago

We don't know what you think a "half-Wilson" mirror is. If you want to compare two circuits, show the schematics of both of them. Also the current would be a step, not "ramping" up and down. Do you mean the voltage ramps up and down to nearly both rails?

Pete W‭ wrote about 3 years ago · edited about 3 years ago

@Olin, sorry for not being more clear. Edited to hopefully clarify what I'm asking. I didn't mean that it is an intentionally controlled ramp, rather that the output (i.e. collector current sunk from the node at the top of the cap) takes measurable time to go from 0 to the value that it will have. I sort-of think the 3rd transistor would bring in extra current from the output side, but maybe this is offset by having another transistor to turn on, hence thought I would post the question.

Andy aka‭ wrote about 3 years ago

Use a simulator. Really, use a simulator. If you are not able to use a simulator let me give you some very, very good and strong advice: Get a simulator and learn how to use it.

Pete W‭ wrote about 3 years ago

@Andy aka -- yes, you are right. It's something I have been avoiding. Thanks for the push to get me there.