[sdiy] Op amp clips prematurely?

[Donald Tillman]

On Feb 2, 2014, at 10:33 AM, nvawter at media.mit.edu wrote:

> However, I was greatly surprised when I began testing my circuit.  I haven't  attached it to the micro yet.  Simply looking with a scope at the op-amp output has shown me a serious issue (4).  While the bottom end of the range produces the expected one-to-one linearity, it appears as if there's a discontinuity where the input range 2.8V to 3.3V all maps to 3.3V.


It appears that the input voltage is beyond the opamp's spec'd common mode input voltage range.

When the input voltage gets high enough the diff amp at the opamp's input gets turned off and the output slams to the rail.

  -- Don

--
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com