2 Replies Latest reply on Feb 18, 2014 3:06 AM by user_14586677

    Analog inputs

    james.marquardt

      Hello all,

         

      I am working with a PSoc3 chip.  First time using the PSoC, and I am wondering can I send a sine wave into an analog input to a low pass filter inside the PSoC?  Since the PSoC is running at 3.3vdc the sine wave will canter on 1.5vdc and swing approximately 1vp/p.

         

       

         

      Is this allowable or is the analog input DC level only?  Also, if the answer is YES that I can send a sinewave into the device, can I take th eoutput of my PWM, and send it through an internal integrator and output a sine wave?

         

       

         

      Thank you in advance.

         

       

         

      Jim

        • 1. Re: Analog inputs
          user_78878863

          Yes, you can send in a sine wave to the PSoC3 - its inputs are perfectly capable to handle AC inputs (up to several MHz, depending on the voltage levels). But you cannot go below ground or above Vdda with your signal - but your proposed signal would be fine even with 3.3V Vdda.

             

          I think there is no internal integrator, but you should be able to build one by yourself using the inernal OpAmps and some external capacitors / resistors. Or you go experimental and digitize the signal and feed it into the digital filter...

          • 2. Re: Analog inputs
            user_14586677

            Always examine data sheets to see if you are working withg R-R Inputs

               

            and outputs, otherwise limited CM range will limit pk-pk swings.

               

             

               

            To offset signals into PSOC you can ac couple to a simple divider that

               

            supplies the offset to the input. Or you can use the following which eliminates

               

            couplig cap, just uses two R's -

               

            http://electronicdesign.com/analog/use-excel-calculate-d-level-shifter-resistor-values

               

             

               

            Excel spreadsheet to calc values attached.

               

             

               

            For PWM integrator, a simple RC network offten surfices. This ap note discusses tradeoff of

               

            settling time and ripple in the RC filter.

               

             

               

            http://www.ti.com/lit/an/slyt076/slyt076.pdf

               

             

               

             

               

            Regards, Dana.