4 Replies Latest reply on Dec 31, 2011 6:51 PM by user_37926942

    Op Amp Modeling


      Hello All,


      I would like to design with the PSoC OpAmp. Does Cypress have a spice model availible for it? If not, is it similar enough to another Op Amp to use a model of the similar op amp in its place?





        • 1. Re: Op Amp Modeling

          Cypress does not have a spice model for the opamp. If not equivalent, the opamp might be similar to some standard opamp. I will let you know the exact details after investigating.

          • 2. Re: Op Amp Modeling



            Is there any update on this?


            The gain bandwidth product of the op amp and other parameters are key to determine if a high Q analog filter can be designed. It would be very helpful to figure out if one's analog filter even has a prayer of working before commiting time and hardware to it.


            Diode Dan

            • 3. Re: Op Amp Modeling



              Figure on a standard opamp model with unity gain-bandwidth of 5 MHz (at high power) and output resistance of about 20 ohms. The standard multiple loop RC-active topology has center frequency that is sensitive to GBW by Q^2. There's another topology in Moschytz and Horn for "medium Q" with feedback to the non-inverting input that is sensitive by only 2*Q (that's bad but better) . For the first case, a typical filter at 170 kHz and Q=5 gets pushed down to 125 kHz and is VERY sensitive to GBW, the second topology gets pushed down to 155 kHz, is less sensitive, but has two more parts so that much more accumulated tolerance error. This is a case where lots of GBW doesn't help. If you design counting on GBW=5 MHz, and we deliver at GBW = 8 MHz, then your design shifts a bunch. As a rough rule, look for GBW = Gain(inband) * Fcenter * Q * 30 for this general topology. PSoC 3 is inadequate for this application by a factor of about 5. If you need better, consider the switched capacitor filters in PSoC1, good to 200 kHz but noisy, or using an external opamp with a whole lot of GBW or trusty inductors and capacitors.


              ---- Dennis



              • 4. Re: Op Amp Modeling

                 It looks like the Q factor can become a problem due to device manufacturing variances. I will probably end up using the DFB or an external op amp for this application.