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Approach to IC design

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Hi,
I woulgd know what is your operative method to design cmos circuit. For example Allen Holberg is a good book for opamp design, but in the "real world" we don't have kn or lambda or VTH0...So, what's your method?
For example for a differential stage, you try with parametric simulation knowing that the current mirror and the current generator determine the ICMR and the differential couple defines the gain?

Thanks
 

in order to start with thte analog design you must do the hand calculations, it is right that the results are far from the simulation but is in the same direction, second it will give you the first values of the circuit then after the simulation you cam modify and improve the design,
the parameter you have to find it from the process specification under the technology you working from
 

senan said:
in order to start with thte analog design you must do the hand calculations, it is right that the results are far from the simulation but is in the same direction, second it will give you the first values of the circuit then after the simulation you cam modify and improve the design,
the parameter you have to find it from the process specification under the technology you working from
Click to expand...

Yes, but you need to know parameters as VT, Kn and Kp and lambda. HOw can you do it? Do they change with W and L?
 

Yes, the parameters depend on W, L a little, but for a rough first calculation, keep them constant.
You can find them by running simulations to characterize the transistors and check device characteristics. That's usual when you start designing with a new PDK.
 

in the hand calculation we will not think with the device parameter variation with T or W and L . we believe that with the hand calculation we are dealing with a very simplified model of the transistor and or the circuit so never expect that you will get the exact result. the simulator will verify your design and any difference you can modify from the simulation. in order to be able to modify you must had understand the circuit theory
 

1. Get all info possible.
2. Usually, the process that you are designing with comes with documentation containing stuff like vt, lambda etc, and also how they vary with process and temperature.
3. Since in MOS design, you can design almost everything with ratios of W/L, we fix the ratios, etc. ( have to to come up with the schematic first)
4. Now, fix L. L is kept the same for convenience, though its easy to find some places where the length is varied over a wide range.
5. Find L from the lambda parameter and the currents that flow through the transistor.
6. Iterate.

Hand calculation results aren't that far from normal results as far as i've seen.
 

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