Current and voltage matching of transistors

What is current matching and Voltage matching, Where its used in Analog layout.

Do you mean current balancing, as in spreading a load across several transistors?

Components can have slightly different specs. One transistor can hog current and burn up.

Balancing needs to be done so that all transistors get the same share of the load.

This is usually done by putting a low-ohm resistor inline with each transistor.

As an alternative you can fine tune each bias until all transistors are balanced. However it's error-prone and can be thrown off by later changes in load, or supply, or drift in operating specs.

---------- Post added at 14:01 ---------- Previous post was at 12:35 ----------

There is also current matching as in testing transistors/mosfets in order to find matching performance among a pair, trio, etc.

And it doesn't have to be for parallel load balancing. It may be to match a PNP transistor to an NPN type, in order to get balanced performance in an AB class amplifier.

Yes, I mean balancing current or maintaing constant voltage in the transistors.
How to achive this in layout because in some schematic they specify current to be matched or voltage to be matched.
I need to know rules to follow ( Ex: like for common centroid distributed, compact,same orientation.....)

For current matching, the current direction can be set to same for better matching.
For voltage matching, the current direction is no so important.

Yes to optimize the current u should do matching like common centroid technique....for more details read "Art of Analog Layout" by Alan Hastings...

Hey Thanks,

Why we use BJT's in 1:4, 1:8 or 24:1 fassion in Band gaps???

They do it again for CC matching

raj1234 said:

Hey Thanks,

Why we use BJT's in 1:4, 1:8 or 24:1 fassion in Band gaps???

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