5 Replies Latest reply on Jul 5, 2015 1:14 PM by user_14586677

    Opamp in PSoC 4 BLE

    iamfantom

       I'm using a PSoC 4 BLE pioneer kit. The opamps do not provide an output voltage in the inverting amplifier configuration whereas the non-inverting amplifier configuration works perfectly.

         

      I'm using the example project provided in PSoC creator and I've attached a zip file of my project.

         

      Could someone please help me out?

        • 1. Re: Opamp in PSoC 4 BLE
          user_14586677

          You have an inverting amp, a G = 1, a 1V input, so output

             

          theoretically should go to - 1 V. But PSOC is a single supply

             

          analog device, no pin can go below ground or above Vdd, actual

             

          values in DC section of datasheet.

             

           

             

          So if you want to interface to PSOC you have to offset Vin to

             

          meet its single supply nature. Provide an offset to the NI input of

             

          the OpAmp.

             

           

             

          So what is the range of the input you want to supply to PSOC ?

             

           

             

          You can use the equation here for Vout, set R2 to 0, R4 to infinity. www.electronics-tutorials.ws/opamp/opamp_5.html

             

           

             

          Regards, Dana.

          • 2. Re: Opamp in PSoC 4 BLE
            user_14586677

            So in short bias the NI input of the OpAmp to Vdd / 2 with a pair of resistors.

               

            Then if Vdd is 5 V as an example, for an input that goes from 0 - 5 V the

               

            OpAmp output will go from 5 V to 0 V.

               

             

               

            Regards, Dana.

            1 of 1 people found this helpful
            • 3. Re: Opamp in PSoC 4 BLE
              user_14586677

              Another way of handling - input signals -

                 

               

                 

              Note this technique of offsetting with R to Vdd allows

                 

              for - input signals and biasing up to Vdd /  2 for max input

                 

              CM range. Also eliminates expensive coupling cap if doing

                 

              an AC coupled design. Use the Excel calculator in zip file

                 

              I posted to determine R values. One negative is input Z be-

                 

              comes the sum of the two Rs used for offsetting.

                 

               

                 

               

                 

                 

               

                 

              www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip

                 

               

                 

              Use the Excel calculator in the zip file to calc Rs.

                 

               

                 

              Regards, Dana.

              • 4. Re: Opamp in PSoC 4 BLE
                iamfantom

                 Hi Dana,

                   

                Sorry for the late reply.

                   

                I didnt know that the OpAmps on the PSoC were single supply. Providing an offset to the NI input of the OpAmp as you suggested worked perfectly.

                   

                Thanks a lot, Dana.

                • 5. Re: Opamp in PSoC 4 BLE
                  user_14586677

                  Glad I could help.

                     

                   

                     

                  Regards, Dana.