7 Replies Latest reply on Sep 25, 2012 9:46 PM by srihari.s

    How good is PSoC comparator.

    srihari.s

       I have an incoming signal of 5vpp which is dc shifted by 2.5V These signals come once in a while and i need to convert these signals to Pulses.

         

      My idea is to compare this value with the 2,5V DC voltage . But this DC voltage may be noisy.....Is this a good idea???? or

         

      I can give the same signal to 2 different amplifiers of different gains and give to comparator....is this a better choice????

        • 1. Re: How good is PSoC comparator.
          user_22393527

          Do you a sine, square, or triangle shaped pulse?

          • 2. Re: How good is PSoC comparator.
            srihari.s

             The incoming is my sine wave........I am sorry about providing info about the incoming signal.....its not 5Vpp......but in the order of few10s of  milli volts around 2.5v dc.

            • 3. Re: How good is PSoC comparator.
              ki.leung

               

                 

              You may need to use the comparator with Hysteresis enabled and with debouncing as well. However you can also have th signal thru filters to remove the noise.

              • 4. Re: How good is PSoC comparator.
                user_22393527

                 My only design (so far) with the comparator was quite good, but I had a 4V p-p square wave coming in. To get the best results I ran it into one of the dedicated op amp inputs, and buffered the signal with the fastest op amp setting. Then it ran it through the comparator, with the good Vref (not the power supply split resistor). It was rock solid, but my wave was sub 10KHz.. Actually, now I recall I have another design that operates on a 1 v p-p sinve wave and the above approach worked just fine.

                   

                If the signal is a few mV it might be worth it to amplify your signal? The opamp offset is 2 mV, and comparator hysteresis is on the order of 10 mV. PGA's are built in (though watch the 3db cutoff), or use external resitor and an opamp.

                   

                I am really bad at calculating things, so generally I go for the build and test approach, I think that may be why I like PSoC, since its really just like a breadboard, but all inside one IC..

                • 5. Re: How good is PSoC comparator.
                  user_14586677

                  Depends on the nosie level as well. You might consider a simple

                     

                  RC LP filter in the input signal path to take out fast L and C transients that

                     

                  might exceed hysterisis levels used. Another way of doing this is

                     

                  to use an OpAmp as a comparator, and set its power level low, hence

                     

                  its slew rate and BW will act as a LP filter to transients.

                     

                   

                     

                  Just some options.

                     

                   

                     

                  Regards, Dana.

                  • 6. Re: How good is PSoC comparator.
                    user_14586677

                    One additional comment. An OpAmp has a compensation cap in it, thats

                       

                    what is key in limiting full power BW (vs small signal BW). Thinking another

                       

                    way, it acts like a LP filter to large transients, as well as its small siganl BW

                       

                    effects. A comparator has typically no compensation cap in it.

                       

                     

                       

                    Regards, Dana.

                    • 7. Re: How good is PSoC comparator.
                      srihari.s

                       My signals are 40k signals. Since the hysteresis is of 10mv, i think i can sustain with the noise corrupting my signals......

                         

                      PGA can act as a good low pass filter...as gain increases the cutoff comes down....But the falloff is 20db per decade so the harmonics of my 40k can easily creep in even though not having high gain......