3 Replies Latest reply on Feb 21, 2013 4:08 PM by DaKn_263916

    Glucose Measurement Using PSoC 3

      Hi to all,


      I am doing glucose measurement , in this i am Interfacing IDAC, VDAC, TIA(Transimpedance Amplifier).Glucose Test Strip gives current so i  am taking IDAC .


      The Output Equation at TIA  Vout=Vref-I*R, Normally for I=0 case Vout= Vref , but here I=0 i.e i am not connecting any thing to terminal , but i am measuring Vout, what i am getting is 0.29v, why is this strange output or else i am wrong any where.i am uploading Image of TOPDESIGN.

        • 1. Re: Glucose Measurement Using PSoC 3

          one Mistake on top post, with I=0, ie not connecting IDAC, not getting any value on multimeter.

          • 2. Re: Glucose Measurement Using PSoC 3

            What is Vref (VDAC8) set to ? With a scope is TIA output DC or noisy, 60 cycle, etc.....




            Per your diagram Pin_6 = Pin_5 as measure din DC voltage.




            The TIA in this circumstance should act as a follower, although you might


            want to disconnect the pin from TIA inverting input to minimize pickup for the


            offset test.




            To get an offset of .29 V with 40K TIA G set R one would have to have a leakage


            of ~ 7 uA, which would be a pretty high bias current for the OpAmp used in TIA.


            I looked for Ibias / Ileakage specs on OpAmp, TIA, saw none. This is just an






            Regards, Dana.

            • 3. Re: Glucose Measurement Using PSoC 3

              I set this up, using 1M Ohm TIA G set R to "aggravate" Ibias and Ileak errors.




              For VDAC = 0                      I got 29 mV of TIA offset


              For VDAC = .512 V              I got ~ 3 mV of TIA offset




              If you look at G error and zero scale error for DAC that pretty much would cover


              the 29 mV I got. To be exact one should calc the spec errors to see what one can






              Regards, Dana.

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