3 Replies Latest reply on Sep 6, 2018 3:45 AM by vsrs

    Rules for Opamp and ADC connection

    morimoto-n_1534561

      Hello,

       

      I would like to confirm the rules for Opamp and ADC connection.

       

      when OpAmp is used for signal amplification.

      - The gain is determined by the external resistance of R1 and R2.

      - The output of the OpAmp is output to the external pin via the 10x buffer.

      - The output of the OpAmp and the input of the ADC have to connected not via the internal wiring but via the external analog pin.

       

      Please review attached pptx file.

       

      Best Regards,

      Naoaki Morimoto

        • 1. Re: Rules for Opamp and ADC connection
          vsrs

          Hello Naoaki san,

           

          Your understandings are right

           

          1. The gain of the opamp is decided by the external resistors as per your circuit.

           

          2. The opamp has an internal(1X) driver and an external driver(10X). 1X output driver is suited to drive smaller on-chip capacitive and resistive loads at higher speeds. The 10X output driver is useful for driving large off-chip capacitive and resistive loads. If the output of the opamp is connected to the SAR ADC, it is recommended to choose the 1X output driver. If the output of the opamp is connected to an external pin, then, choose the 10X output driver. As your case is a combination of both, 10X output is selected automatically as output is given to a pin. There is no problem in using this configuration.

           

          3. As per your schematic, the pins have to be connected externally. You may be able to do it with a single pin too. In that case you have the schematic will look similar to this.

           

           

          Best Regards,
          VRS

          • 2. Re: Rules for Opamp and ADC connection
            morimoto-n_1534561

            Thanks for the reply.

             

            In your diagram, OpAmp is connected to the external pin and is set to use 10x Driver.

            However, it is not a problem to connect to ADC with internal wiring, right?

            Best Regards,

            Naoaki Morimoto

            • 3. Re: Rules for Opamp and ADC connection
              vsrs

              Hello Naoaki san,

               

              Connecting using internal routing is not an issue. Only thing is that as the complexity of the project increases routing can get congested and at some point routing will not be possible with the available resources. One more thing you can check is that the route taken in CYDWR -> Analog tab. If it is complex, the route will add additional resistance from Opamp output side to ADC input side(switch resistance + route resistance). You can use the ohm meter feature to see the approximate value of the resistance.

               

              Best Regards,
              VRS