How to represent input offset voltage of opamp?

[treez]

Hello,

I am trying to add an offset voltage of 4.5mV into each of the opamps U1 and U2 in the below schematic.
(in the actual circuit, the MCP601 opamp will be used rather than LT1006)

Have i put the offset voltage source in the right place? (right way round etc)?

 

[FvM]

What do you mean with "right way round"? Offset voltages have accidental magnitude and polarity, up to specified limits. Normally distribution over a large production lot can be expected. Spice models have sometimes already a build-in offset voltage source.

 

[treez]

What do you mean with "right way round"?

...i think you answered it by saying they are "accidental"

Should i have connected those voltage sources in the other way round, or as they are?
.........................im certain the LT1006 model has no built in offset voltage...ie v(offset) = 0V.

 

[FvM]

Both or none at all. Depending what you want acheive.

 

[rahdirs]

im certain the LT1006 model has no built in offset voltage...ie v(offset) = 0V.

LT 1006 has a low offset of 20uV.
Even in chopper stabilized op-amps,offset is < 1uV but not zero.

 

[manojdharap]

Do not understand your query completely.
First question is do you want to add off-set voltage intentionally to actual circuit or do you want to add it for simulation purpose?
If you want to add it for simulation purpose, you can go to part properties (dependent on tool you are using) and add it and if you want to add intentionally, then voltage source is right thing.

But as a designer, I will not prefer to have multiple voltage sorces with this much low voltages, instead I will prefer to have gain adjusted in such a way that it will compensate off-set voltage.

 

[FvM]

The comment in post #1 suggests that the intention is to evaluate the effect of varying OP offset voltages in simulation. We'll usually want to find the worst case output respectively input referred offset voltage.

 

[LvW]

For simulation purposes, the right (larger) part of the circuit needs a ground connection.

 

[crutschow]

You likely need to simulate with both offset polarities for each op amp (one at a time) since there are some combinations that may actually tend to cancel each other in the circuit. You can do that with a .step function in LTspice.