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How to simulate the input-offset voltage ????

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firry

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input referred offset

Hi,
How to simulate the input-offset voltage and the systematic offset voltage of an op amp??
 

Vamsi Mocherla

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measuring input offset voltage

Put the Opamp in Open loop configuration and tie one of the inputs to bias level of VDD/2. To the inverting input, give another DC source and start sweeping the voltage till the ouput is at VDD/2. The input voltage will give input-offset/Systematic Offset Voltage. Make sure that you do very small increaments.

Another way to measure the systematic offset is to tie both the inputs to VDD/2 or some other comfortable bias level. Measure the output voltage. Now, input referred offset would be [Vo- (VDD/2)]/ DC gain of the amplifier

I hope that the point is clear
 

firry

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how to simulate input offset

Vamsi Mocherla said:
Put the Opamp in Open loop configuration and tie one of the inputs to bias level of VDD/2. To the inverting input, give another DC source and start sweeping the voltage till the ouput is at VDD/2. The input voltage will give input-offset/Systematic Offset Voltage. Make sure that you do very small increaments.

Another way to measure the systematic offset is to tie both the inputs to VDD/2 or some other comfortable bias level. Measure the output voltage. Now, input referred offset would be [Vo- (VDD/2)]/ DC gain of the amplifier

I hope that the point is clear

Thanks!
 

beckette

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how to measure input offset voltage

that's ok.
another way:put the opa in unit gain configuration, sweeping the uninverting input, the output voltage is the offset voltage.
 

pfd001

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measuring input referred offset voltage

That's misunderstand. Normally the dominate input offset is not the system offset. you should use a monte carlo analysis to simulate the input offset due to the mismatch
 

advaita

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simulate amplifier offset voltage

Vamsi Mocherla said:
Another way to measure the systematic offset is to tie both the inputs to VDD/2 or some other comfortable bias level. Measure the output voltage. Now, input referred offset would be [Vo- (VDD/2)]/ DC gain of the amplifier

Hi

I think that measuring the systematic offset at any convenient input bias won't be helpful - Systematic offset changes with the bias voltages in the situation your op-amp is put into. So, better will be to simulate the op-amp with its actuial stimulus and see the difference in its input signals. Makes sense?
 

findsriharsha

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I know this is an old thread, but would like to add few points for any novice designers:

We need to run monte carlo sims across worst case PVT to get "RANDOM" input referred offset.

For systematic offset (which is not random, but caused by bad design may be :roll: ), it will show up in typical PVT sims only.

For both random and systematic offset, I think sweeping input Vip across input CM range while Vin equal to VDD/2 (as mentioned above by some designer) is the best way I believe.
 

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