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what is the need of matching for analog circuits, i want technical reason. can anybody tell me pls. which type of gradients will reduce by using matching and how?
The functionality of analogue circuits usually depends on either symmetry between devices, or precise ratios. For example, if you're making a differential pair, you will (most likely) want the transistors to be exactly the same, or the circuit behaviour will be funny. If you're making a current mirror, then mismatch will result in an output current which is different than what you intended.
Matching is very important in precise analog circuits like ADCs , if you take a differential amplifier as an example , you need the differential pairs matched to each other so that they behave in the same manner across PVT variations , and so , they would have a good CMRR , and this gives immunity against common mode noise ,also , in current mirrors , usually you need accurate mirroring ratios , and so , you need the transistors to be matched as possible as you can , matching decreases systematic offset as well , ....
Any analog circuit....its performance is highly dependant on the precision of the device parameters and accurate ratios. And if u consider a wafer, the device parameters are not uniform throughout the wafer, every device will have atleast some kind of mismatch which results in not so good performance of a analog circuit.
Mismatches can be variation of threshols voltage, (W/L), channel length modulation, and any other device parameters and care must be taken to see tht mismatch is negligible.
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