On Fri, 2005-12-02 at 09:05 +0000, Luis Moreira wrote:

> I am building an integrator circuit using an OPA627 and I got the
> integrator to generate the ramp I require, but what I need also is to
> when the integrator reaches a certain point on the ramp, which will be
> variable, I need it to stop integrating.

Luis,

Another option to make the integrator stop integrating is by feeding it a
function whose integral is zero. This is hard to achieve in practice, but
one possibility is a high frequency square wave. Many years ago I needed a
DAC, but only had a spare opamp and an I/O pin. So, I created an
integrator from the opamp, and applied a step function to the input to
achieve a ramp and then a high frequency square wave to achieve a small
amplitude triangle wave. The small amplitude triangle wave approximated
the DAC output I needed. I had the luxury of milliseconds though, so I
doubt this is possible with your circuit.

The output looked something like:

     /\/\/\/\/\
    /
   /
  /
 /
/


Scott

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