OPA615 as an integrator

Hello Nico,

I tried to get that circuit to work , but I could not.  I am not familiar enough with this part to offer any good suggestions. 

I did see that the IQadjust pin was not connected.  I put a 300 Ohm resistor to ground and the circuit does not ring anymore, but the integration function still does not look correct. 

You may try posting this question in the amplifiers and other linear section. 

http://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/default.aspx

Hello Nico,

Here is a possible circuit to integrated a small pulse.  Note that the integrator is done using the SOTA, so the cap selection on Chold needs to be adequate for teh pulse and amplitude range you want to measure.

I eliminated the feedback network as this was the root for the decaying oscillation you were observing.  Instead I am using the fact that you have a pulse on the input and am using it to control the S/H pin.

5732.OPA615_ns_pulse integrator.TSC

Hi Nico,

I do not see much for possible improvements.  The two things that can be done is try to minimize the droop.  It seems that a large portion of the droop is cause by the transistor used for reset.  A CMOS transistor may do better here.

The other possible improvement would be to provide additional gainto the output to help separate the amplitude further.  This can be achieved by using the C output as the may output and providing a 200ohm to 500ohm load resistance.  Note that this node would have to be buffered to the next stage if used that way to maintain the impedance.

4010.OPA615_ns_pulse integrator-2.TSC

Hi Xavier

Is the way in which i can still get the same results by ommiting the VCVS, This is beacuse it is a bit impractical

Can i run the simulation with another device on the place of the VCVS?

Thanks

nico

Hi Nico,

Yes, you can use an amplifier in a gain of 5V/V configuration.  An ideal amplifier would make it an easier setup.

Best regards,

Xavier

Hi Xavier

You are right that the ideal op-amp is the easier setup, i tried that and it worked, but again i need to be practical and use a 'real' op-amp as in the circuit attached. Results are undesirable.

How would you advice on the real op-amp setup

0820.resetting pulses of different amplitudes%80nschold real amplifier.TSC

Thanks

Nico

Hi Nico,

You will need and amplifier that is capable of high gain, depending on your signal and low propoagation delay.  I would recommend starting with the OPA695.