What is the MOS matching?

Hi 2 all,

What's a MOS matching ???

gafsos

Re: MOS matching

To make a mos as same as another one~~. such as the input pair of OP, current mirror......... Reading textbook will help you

Re: MOS matching

MOSFET matching means making two or more MOSFET equal in terms of device geometry. For simplicity, you draw two MOSFET with the same size means "matched"
In reality, they are not equal in size since they face device differences independently during fabrication. That's why ppl always find ways to make sure
the devices drawn to be exactly the same as the other. This is the idea of matching.
How we can acheive that? By careful layout using common centroid approach and add dummy transistors to smooth out the profile across the devices.
In real silicon, two transistors can NEVER match with one another but to a degree it is acceptable and therefore ppl always find ways to compensate it. For example, input offset from Op-Amp input pair, and ppl used for example, auto-zero-ing to compensate the mismatch between input pair

Re: MOS matching

Not only the MOS, the resistor, the capacitor and the biploar also needs too care about matching.

Re: MOS matching

Hi comrade Che,

Say you have a differential pair. All the characteristics of the Transistors should be identical in order to achieve best amplification and have less secondary effects. Basicly is as hung_wai_ming described.

After designing the circuit you have to layout it to a physical body. When you try to implement in a waffer then you understand that whatever the technique, you will have impurities, differences from mm to mm on the waffer wich will finnaly effect your identical characteristics on the design.

many techniques are for compensating matching. hung_wai_ming gave the designing techniques, but in layout you also have physical implementation that will minimize the mismatch :

1. Cross quad: Working for pairs or quads or even number of devices. Instead of putting the devices next to each other, you break it to half and you are forming a quad where M1 ( Tr1) will be implemented with one half on the upper left corner and the other half on the lower right. Same applies for M2 (Tr2). working symmetrrical with the interconnection, you have minimized any mismatch effect caused by non-identical matterial of the two Transistors.

2. Dummy components. Say you have 3 resistors. You put them one close to the other. But the resistor in the middle has a resistor to each side. The two others doesn't . You create a dummy resistor ( same or smaller but standing on the free side of the other two.

3. Say you have 3 transistors you have to match. Cross quad doesn't apply here. You can make it like cross quad with 6 pairs. You can make the two cross quad and split the other one on both sides of the square, etch, etc.

There are many techniques for compensating mismatch. All derived by the fact that technology can not yet achieve the ultimate waffer and the ultimate creation of a chip. Therefor you should take could care when you layout an IC .

D.

Re: MOS matching

Hi ,

Mos Matching represents , preventing the MOS form process variations . During fabrication tox is not same throughout the die it varies . If A and B are two Mos transistors ( Which can be diff amp , current mirrors ) having 3 fingures each, if u place side by side due to process all parameters of MOS will change , by which A and B will not act as same . To avoid this mismatch between A and B we go for device matching ( Matching may be Common centroid or Interdigitized ). Dummies are placed for outer side transistors to prevent from etching variations .

Best Regards ,
Madhu