7 Replies Latest reply on May 12, 2010 8:16 AM by userc_42488

    Diff Amplifier

      I have a serious problem with a simple DiffAmplifier.

          I implemented the diffblock placed into example 1 in AN2041 example:   
          My intention is to implement the programmable current source showed at AN2089:   
          Basically my problem is that I’m not be able to obtain the differential signal.   
          I get properly the common mode but not the differential.   
          I studied the SC Block in detail and the correct parameters,  and these look like to be right   
          As the example shows for the DiffBlock I put the Diff SC Block and the global resource parameters:   
          - The DiffBlock parameters as in the first paper commented above.   
          Global params:   
      • Slepp Timer: 512 Hz.
      • Sysclock/ Power: 24MHz, +5V
      • VC1= SysClk/6
      • VC2=SysCLk/4
      • RefMux: Vdd/2+-Bandgap
      • Analog Power: SC On/ Ref Hi

      Are equal than an example I found working with the same parameters in:



          Where implement the two examples.   
          Please don’t send me the AN2367 document:   
          I want a unipolar output differential amplifier nor a two outputs diferential amplifier.   
          I don’t know whats going on and I tryied many options.   
          Someone can help me?   
          Thanks for all.   
        • 1. Re: Diff Amplifier

          Did you try the project file that comes with the application note?  Are you trying to modify the project to suit your needs?  If you need a working project for the current source, I have one, but I am not able to attach a file here.  If you can give me your email, I can send it to you.


          Best Regards, Ganesh

          • 2. Re: Diff Amplifier

            I can work that proyect direcly because I have another part, concretely


            I have work with CY8C24994 from the CY3214 PSoCEVal USC KIt Starter.


            It looks like easy and I know know quite deeply the values I must to intro into the SCBlock, but it don't works. They are designed for SC Blocks type A and B and I have B and C, could it be a problem?


            Anyway, my email is: mmoron21@gmail.com


            Thanks for all and I will comment you my progress.


            By the way do you understand completely the SC Blocks?


            I have read twenty times the Understanding Switched Cap Blocks, and I still don't understand some thinks.


            See you and thanks again.

            • 3. Re: Diff Amplifier

              One issue more.


              With RefMux I select the reference levels, but how knows the SCBlock if must to point to AGND, RefHi or RefLo in φ2 ?


              Handling the  ascXXcr3 register you can do it, but in many times, how in the case of the DiffAmp or the current source, it's not specified.



              • 4. Re: Diff Amplifier

                There are structual difference in the Type A/B and Type C/D SC blocks. You can reference the user mdoule datasheet for details. The datasheet can be found at C:\Program Files\Cypress\PSoC Designer 5\Documentation\User_Module_Datasheets\StdUM.

                • 5. Re: Diff Amplifier

                  Many thanks,but I know by heart the SC diagrams, the problem is if the


                  current sources implemented into SC blocks Type A and B works properly


                  implemented into type C and D. There's only slightly differences between them, mainly


                  in the Autozero and BSW switches commented in detail in the document:




                  and in the SC datasheet you commented above.


                  Mi problem is that I don't see the difference.


                  When I try to draw the scheme for phi1 and phi2 cases I don't see very well what is going on.


                  My current source don't works.

                  • 6. Re: Diff Amplifier

                    Can you please zip and attach your project here?

                    • 7. Re: Diff Amplifier

                      Yes I can. Here you have.


                      I studied deeply all the SC Block parameters and there are


                      fixed at the proper value. In fact this example comes from the AN2041 paper and you can find


                      another example in the AN2089 paper.


                      The strange is the common mode source and the gain invert works properly, but


                      the DiffBlock don't do it. So I'm not sure if my part is damaged or I'm doing something wrong.


                      Thanks for all.