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Explanation of mismatch and dummy devices

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Newbie level 6
Dec 13, 2005
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1.what is the mismatch of devices.
2.what is the full strapping in detail.
3.what is the exact coupling in devices.
4.what is capacitor matching.
5.i know what is dummuy device and what are the advantages of it in various applications.
6.what is the critical or HV signal widht requirement. can we convert lambda to micron rules.


advantages of dumys is to createt same environment

then to suit comon centroid configuration when evev devides are nott present

to equalise the offset of etching in a group of divices for all the devices

Re: I have some doubts

Mismatch is the major concern in the analog layouts which will arise due to the random mismatches and systematic mismatches. some examples of the mismatches are offset mismatch,gain errors....u can eliminate these partially by matching the devices properly (using common centroid layout techniques...).the mismatch mainly depends on the device geometry.large area devices produces less mismatch.again for the capacitor matching same resons.u can follow the common centroid technique to eliminate the stress ,temperature gradients.

Dummy devices serves a greate role in analog layouts in creating same environment and most importently they will save the original devices from the over etching and under etching processes.

lambda rules are process dependent and they will provide eqivalent of lambda in terms of microns.

It is the minimum width of the metal required to handle the current through that particular net. Genarally we used to take 3-4 times the critical width for the reliability issues.

I think i've answered most of ur querys.

Re: I have some doubts

Mismatch is a time independent random variation in identically designed elements.

It can occur due to process,electrical parameters.

Gradients between the two identically designed devices can be eliminated by arranging the devices in common centroid or interdigitiged pattern depending on the requirement.

Idea of placing the dummy device is to create same environment there by yielding less mismatch.Let me explain with example U have A(1) B(2) to be matched,we know tht

B A arrangement cacels gradients in both direction.But we have A(1) not two.

B Dummy

Dummy acts like another A device PHYSICALLY but not electrically.

There by satisfying the common centroid rules to have better match.

Capacitors will follow the same rules of matching with others except Random mismatch.

Width of the metal can be selected using DC level of the signal Rather than the AC

Width is decided by current density of tht material.Analyze the Blck's equation for more expertise.

If anything Un answered to the point ,U can bring out for the discusssion

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