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Design >> Mixed-Signal Design >> Random voltage offset
https://designers-guide.org/forum/YaBB.pl?num=1160508951

Message started by bharat on Oct 10^th, 2006, 12:35pm

Title: Random voltage offset
Post by bharat on Oct 10^th, 2006, 12:35pm

I am looking for good paper/material for voltage offset.

I am not sure how the followings are related: systematic offset, random offset, input referred offset. Can I say systematic offset and input referred offset are part of random offset ?
Please correct me, if I am not:
Systematic Offset: It is due to geometry/dimension (Width as well as Length) mismatch of the devices during fabrication.
Input Referred Offset: It is due to doping concentration variation of the diffusion, oxide thickness varition which results in Vth variation
The combination of above two is called 'random offset' ??
If so, what offset the simulator shows (without adding any Vth variation of channel lenght variation), what is that offset. Is it random/systematic/input referred

Thanks
-Bharat

Title: Re: Random voltage offset
Post by SATurn on Oct 10^th, 2006, 1:39pm

You can have a look on Prof. Sansen's textbook (Analog CMOS Design). Just I would like to add that systematic offset comes from some kind of asymmetry in your circuit even if all devices are well matched. For example different Vds of two NMOS current sources. So, when you run the simulator in normal condition (not statistical simulation), what you see is just systematic offset.

Title: Re: Random voltage offset
Post by loose-electron on Oct 19^th, 2006, 1:34pm

Let me propose some definitons here -- 8-)

Systematic Offset: Due to the circuit design characteristics, with all circuit elements perfectly defined as the ideal element model. All thresholds exactly the same, all currents exactly the same for 2 transistors of the same size. Two 1K resistors are both equalt to 1000.00000 ohms. An op-amp with low open loop gain, will have a systematic offsets due top the fact that the ideal op-amp has infinite gain.

Random Offset: Due to non-ideal circuit elements. Slightly different drain currents between two "identical" transisotrs. The 2 resistors one being 999 ohms and the other being 1004 ohms.

Input Referred Offset: Take all the sources of offset and mismatch. Sum up all their effects and approximate it as an equivalent number at the input of the system. Similar to "input referred noise" in thinking.

Hope that helps -
Jerry
8-)