5 Replies Latest reply on Jun 29, 2011 4:29 PM by maria.josep.lopez

    Feed PSoC with an AC signal

    maria.josep.lopez

      Hi,

         

      I'm trying to feed the PSoC with an AC signal and I have doubts how to do it. I configured the PSoC with: 3-OPAM and ADCINVR. The AC signal is providing by a wien oscillator so exist a gnd there. I don't know if to design the wien oscillator I have to take in account the AGND (2.5V) of the PSoC.

         

      Now I'm trying feeding the INV- of INSAMP with AGND (refmux) and NOINV+ directly with the output of the wien oscillator.

         

      Is this method right?

         

       

         

      Thanks for your support!

         

       

         

      Regards.

        • 1. Re: Feed PSoC with an AC signal
          maria.josep.lopez

          Hi everyone,

             

           

             

           Could someone help me with this issue?

             

           

             

          Thanks for your feedbacks!

          • 2. Re: Feed PSoC with an AC signal
            graa

            Check out the below blog post.  Let me know if this helps.

               


               

            http://www.cypress.com/?rID=50815&cache=0

               

             

               

            Best Regards,

               

            Ganesh

            • 3. Re: Feed PSoC with an AC signal
              maria.josep.lopez

               Hi graa,

                 

               

                 

              thank you for your post! It helped me. Now I connected the AGND (output of RefMux) to the gnd of the circuit (for making the same AGND in all parts, as it said in the post). Then, I have connected the signal AC in the pin NOINV the INSAMP and the AGND of the circuit to INV (will it be the same as connected directly to the output of Refmux, isn't?).

                 

              I would like to ask you also, if the result I saw in the LCD (using INSAMP and ADCINVR) I have to subtract 2.5 to obtain the real value? Because, all circuit considers AGND of 2.5 so, is like it existed a DC component that move the real signal to treat it in the PSoC.

                 

               

                 

              Could you tell me if I'm in the right direction?

                 

               

                 

              Thanks for your feedbacks!

                 

              Regards,

              • 4. Re: Feed PSoC with an AC signal
                graa

                If the ground of the input signal is isolated from the VSS of the PSoC, then yes, you are in the right direction in connecting the input signal to the PSoC.

                   

                 

                   

                Regarding the ADC output and the 2.5V offset, if you set the ADC's Data Format to "Signed", the  the ADC will work with AGND as the reference.  ie, if the input AC signal is 0V, then ADC output will be 0, if input signal is +ve, ADC output will be +ve.  if input signal is -ve, ADC output will be 2's compliment -ve.  So, you do not have to subtract any value from the ADC value.

                   

                 

                   

                Best Regards,

                   

                Ganesh

                • 5. Re: Feed PSoC with an AC signal
                  maria.josep.lopez

                  Hi Graa,

                     

                   

                     

                  thanks for your confirmation.

                     

                  I asked you this (substract 2,5) because I'm using the INSAMP, 3-OPAM, and I saw in the datasheet of this module that the output will be: Vagnd+G*(Vdiff) so, is like the signal always goes with this offset... This equation made me think that perhaps in the signal output or the value I was seeing in the LCD was with 2,5 added. However, I saw that the configuration 2-OPAM has an Vref added but, in this case you can choose the reference, isnt?

                     

                  Which one is better to treat an small voltage AC signal? There are a lot of difference in using one or other?

                     

                  Thanks for your reply!

                     

                   

                     

                  Regards,