factors affecting current mirror

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lucky8

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Hi,

I would like to ask, what are the things that i need to consider for simple current mirror.
I know that the output current of the current mirror is linked to the emitter area of the transitors and the avalanche voltage, VA.
What other factors that i need to look upon for this current mirror?
 

base current, and mismatch, output resistor, perimeter
 

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    lucky8

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You might find some info you need in an old article I wrote.
**broken link removed**
it is not exactely the same, but closely related.
 

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    lucky8

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the main factors sre

matching

output volatge

voltege swings

the impedane at the inputs of the transistor may cause errors.
 

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    lucky8

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output voltage?
do u mean the VCE?

I've read that the output impedance is the measure of the current mirror quality, and how is that?
 

lucky8 said:
output voltage?
do u mean the VCE?

I've read that the output impedance is the measure of the current mirror quality, and how is that?
Click to expand...

An ideal current source is simplay a current source with an infinite shunt resistor.

So, the higher the output impedance of you mirror the less it will be susceptible to load variations. Generally, a current mirror can drive a low impedance node with no problems. Having a high output resistance means you can drive higher impedance nodes with the current source or, alternatively, you have a high quality current source
 

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    lucky8

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You can try for a better performance using cascoded transistors. It will give you a better matching between the 2 currents (you have a much higher output resistance)
 

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    lucky8

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