LM139A: Polarity of input offset voltage

John Vranes

Part Number: LM139A

Hello,

The datasheet for LM139A specifies an input offset voltage but only shows it as a positive value. Does that mean that the input offset voltage is always going to be a positive value, or can it also be a negative value (and polarity is simply left off intentionally in the datasheet)?

Thanks,

John

over 5 years ago

0 Paul Grohe over 5 years ago

TI__Guru 52776 points

Hello John,

Offset is modeled as a voltage source in series with the positive input.

See section 2 of the TI Precision Labs series on Offset voltage

TI Precision Labs - Op Amps: Input Offset Voltage and Input Bias Current

So if there is a positive offset voltage, it raises the effective threshold voltage (assuming the reference voltage is on the non-inverting input). If the reference is on the inverting input, a positive offset would lower the effective threshold.

Obviously, a negative offset would reverse the above...

0 Paul Grohe over 5 years ago in reply to Paul Grohe

TI__Guru 52776 points

Hello John,

Ooops..the rest of your question was "below the fold".

Offset can be positive or negative. Always assume the offset number is +/- unless specifically stated with a negative only sign, or a note.

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LM139A: Polarity of input offset voltage