input buffer question


I am trying to interface to an oxygen sensor and am interested in a circuit with the following characteristics.

low output impedance. single rail bias into the 0 - 12V range. High input impedance (~1Mohms)

I have seen many single rail op amp applications, yet they all require either zener diode (frequency problems - especially low frequency) and resistor ladders which place the input impedance into the 50kohm range i.e. two 100k in parallel.

Anyone got any ideas how to build a simple single rail input input buffer that yields > 1Mohm input resistance and relatively good low frequency performance?

Thanks in advance


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Don't most (automotive) oxygen sensors produce a 0 to 900mV output, with no external bias needed? Any single-supply opamp follower or non-inverting amplifier should work fine.

I imagine you'll want a 10M resistor to ground, etc., so the opamp input won't be "floating" during the open condition the oxygen sensor exhibits when it's cold.

    - Win
Reply to
Winfield Hill

The kind of oxygen sensor I'm familiar with is essentially a battery, albeit one with quite variable internal resistance (essentially open when cold, as you say). The voltage out is determined by the Nernst equation.

Best regards, Spehro Pefhany

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Spehro Pefhany

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