7 Replies Latest reply on Jul 5, 2014 5:01 AM by user_14586677

    current amplification

    prakhar.kumar
        • 1. Re: current amplification
          prakhar.kumar

           hi, I am using a cd pick up head. i want to properly amplify the very small output current of the pick up head using psoc. i used an opamp as a TIA but it did not show any variations in output voltage when a cd was brought neare or taken away from the pick up head. any advice? 

          • 2. Re: current amplification
            user_1377889

            Do you have a datasheet of your pickup head?

               

            Can you post your complete project, so that we all can have a look at all of your settings? To do so, use
            Creator->File->Create Workspace Bundle (minimal)
            and attach the resulting file (do NOT use chrome, that still may not work).

               

             

               

            Bob
             

            • 3. Re: current amplification
              user_14586677

              I would start by setting TIA w/ NO capacitive fdbk. Reason

                 

              is if you have to take very high G to get a signal, then BW

                 

              drops like a rock. Also look into the bit rate you will be getting

                 

              off head. This may be beyond the TIA's capability. Further look

                 

              at using differential signaling, to get rid of CM pickup in the design.

                 

              And / or spend some time making sure power supply noise is

                 

              fairly low relative to signal, especially if you are single ended.

                 

               

                 

              How do I know what the recording speed of a CDR or CDRW is?
              The speeds are designated by multiple factors.
              Example: 1X, 2X, 3X, 4X, 16X, 32X, 64X.

                 

              What do these multiple factors mean?
              The multiple factor indicates the transfer speed of information between a reading / writing / recording / burning drive to the CDR or CDRW disc.

                 

              Multiplied by what?
              The base transfer speed used for calculating Total Transfer Speed is 150 kilobytes per second or 150KB/s. Examples:
              1X = 150KB/s 4X = 600KB/s
              2X = 300KB/s 8X = 1200 KB/s or 1.2MB/s

                 

               

                 

              A lot of CDR designs these days signal condition right at the head,

                 

              for obvious reasons.

                 

               

                 

              Regards, Dana.

              • 4. Re: current amplification
                prakhar.kumar

                 Thanks for the reply.

                   

                I initially used the TIA itself with no feedback cap. due to BW limitations. But it simply failed to produce any observable changes at the output voltage. Is it possible that the current signal from photodiodes of the pick up head is to low to be sensed by the TIA? Moreover, what should be done with reference voltage of TIA?

                • 5. Re: current amplification
                  user_1377889

                  Did you see the equation in the datasheet

                     

                   

                     

                  Vout = Vref – Iin × R

                      FB   

                   

                     

                   

                     

                   

                     

                  Bob

                  • 6. Re: current amplification
                    user_1377889

                    Forum SW clobbered input, it is RFB

                       

                    Bob

                    • 7. Re: current amplification
                      user_14586677

                      The reference would set the dark current output from the TIA.

                         

                      Then depending on the way you wired sensor, sink or source

                         

                      into the Rfb, the output goes up or down from that point.

                         

                       

                         

                      Also sets reverse bias on Photodiode.

                         

                       

                         

                      Yes you could have a photodiode with current so low, nA range, that

                         

                      there would be neglible output. Or one that is already preconditioned.

                         

                      Have you set it up on the bench with rev bias, light source and a dark

                         

                      shutter to check out with DVM ?

                         

                       

                         

                      Regards, Dana.