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Problem: Input impedance simulation of chopping amplifier

zhanghao

For my design of chooping amplifier, a postive feedback loop has been added to boost impedence. When I do the input impedence simulation by PSP, ZM is shown as following. . The results is very strange because he value decended in low frequency. As all known, the impedence should be higher in lower frequency. I cann't understand the reason. So I wonder if it is rightI the usage of ZM in PSP simulation. I also find the method of calculating the impedence like   

And I do the calculation in Cadence, the result is , the value is so minimum than that in the  PSP simulation. So I wonder that the input impedence of amplifier is simulated or  calculated in cadence, which is right? I appreciate it for your any suggestion.

Parents
  • zhanghao

    Dear Andrew:

           I appreciate it for your reply. My versions of my cadence are IC616 and MMSIM141. The chopping frequency is 1k Hz, and the input signal frequency is 100 Hz. In following pictures, schemetic of circuit is shown in fig1. PSS setup and PSP setup is shown in Fig.2 and3, Fig.4 shows the simulation impedence by PSP(several hundreds of MagaOhms). And Fig.5 shows the calculated results (several hundreds of KiloOhms).According to So there is a big difference for the results shown in  Fig.5 and Fig.6. which is real value of input impedence.? I am very uncertain. Hence, Would you tell me how to simuate the input impedence with cadence tools, by PSP simualtion or by calculator or other better methods? Thanks for your time.

                                                                                                                                                                                                                    sincerely

                                                                                                                                                                                                                   Hao Zhang

      

                                        Fig.1

                                           Fig2

           

                                                                       Fig3

                                                                                                            Fig.4

                                                                                                                                    Fig5

    Fig6

Reply
  • zhanghao

    Dear Andrew:

           I appreciate it for your reply. My versions of my cadence are IC616 and MMSIM141. The chopping frequency is 1k Hz, and the input signal frequency is 100 Hz. In following pictures, schemetic of circuit is shown in fig1. PSS setup and PSP setup is shown in Fig.2 and3, Fig.4 shows the simulation impedence by PSP(several hundreds of MagaOhms). And Fig.5 shows the calculated results (several hundreds of KiloOhms).According to So there is a big difference for the results shown in  Fig.5 and Fig.6. which is real value of input impedence.? I am very uncertain. Hence, Would you tell me how to simuate the input impedence with cadence tools, by PSP simualtion or by calculator or other better methods? Thanks for your time.

                                                                                                                                                                                                                    sincerely

                                                                                                                                                                                                                   Hao Zhang

      

                                        Fig.1

                                           Fig2

           

                                                                       Fig3

                                                                                                            Fig.4

                                                                                                                                    Fig5

    Fig6

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