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Unsolved step response problem in Spectre transient simulation

ringamplifier

Hi guys!

I am currently designing a current feedback instrumentation amplifier (CFIA), which is shown in Fig. 1. In this amplifier, Gm2 is the input stage, Gm3 is the feedback stage and Gm1 is the output stage. The gain of this amplifier is set by the feedback resistor R1 and R2 (assume that Gm2=Gm3), which is (R1+R2)/R2. The value of the gain is 50 V/V in my case. 

 

                                                                                       Fig. 1

Now I want to test the step response of this amplifier. So I insert a vpwl voltage source V1 between the two input of Gm2.  V1 will generate the voltage step and ideally Vout will produce a amplified version of the step. 

The setting of V1 is:

Time 1  Voltage1

   0s           0V

Time2   Voltage2

  1ns         40mV

Time3    Voltage3

100ns      40mV

The simulation result of Vout is plot in Fig. 2. Unexpectedly, something like ringing happened

                                                                                                                                                                          Fig. 2

But I changed the Time 2 to 50ns, the Vout seems normal again. Result is shown in Fig. 3

Time 1  Voltage1

   0s           0V

Time2   Voltage2

  50ns         40mV

Time3    Voltage3

100ns      40mV

                                                                                                                                                                              Fig. 3

I hope anyone can give me  a hand! Thanks!

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  • Mikexay

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    community.cadence.com/cadence_technology_forums/f/38/t/22633

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  • Mikexay

    here:
    community.cadence.com/cadence_technology_forums/f/38/t/22633

    Learn Vietnamese online( free for all cadence's members ):

    Lession 1: nho ninh thuận

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