DIY-WB... It's alive...

[Chris Conlon]

At 12:55 PM 9/3/01 -0800, Ludis Langens wrote:

>rr wrote:
>> 
>> The spec sheet for the LM9044
>> makes no mention of a bias voltage output to the O2 sensor.
>
>The data sheet I have does mention a bias.  Check the spec called
>"Non-Inverting Input Bias Current".  The typical value is +/- 380
>nanoAmps.  (In other units, 0.00000038 amps.)

That bias current is not intentional, it's an artifact of real world
devices as opposed to ideal op-amps. If they could make an op-amp
with zero input bias current, they would. (Modern devices are damn
close, too. Picoamp bias currents are not uncommon.) The value is
spec'ed for you so you can determine how much noise voltage will be
generated at any given source impedance. Basically this value is
telling you how much current the amp will draw from (or supply
to) the input.

Now I don't know one way or the other about the correct answer to
the original question (where does the 0.450v bias come from), but
I can tell you that the input bias current isn't part of the answer.

   Chris C.

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