How to TIA AC simulation to characterize tranimpedance?

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prcken

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How to do TIA AC simulation to characterize tranimpedance?

since the transfer function of a TIA is transimpedance, how to plot that with cadence spectre?
it has only voltage and current plot options in AC analysis, i set input AC current to 1A, My question is
1. the transimpedance AC response is just the output voltage magnitude
2. or add a series voltage source (set to 0V) between input bonding pad inductance and the input of the TIA, then translate the transimpedance with output voltage divide that voltage source current? I found the current of that 0 voltage source i added is frequency dependent for there is photodiode parasitic cap and bonding pad inductance.

the latter method shows a better transimpedance vs frequency plot

Thanks!
 
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It depends on what you want to measure: if it is the transimpedance of the (isolated) TIA alone, your method 1. is right if you remove the other elements (photodiode and bonding pad).

If you want the transimpedance measurement of the TIA in its application environment, method 1. is also correct: of course a part of the injected current will be "used" by the parasitic elements (and so is not available for the TIA input), but this is exactly what you want for this type of measurement: the transimpedance in your application environment. I think you don't need the 0V voltage source to measure the current (it's a short circuit anyway), you can still calculate with your unit (1A) current.
 

i want to characterize it in application environment. the input signal will be bandwidth limited too, since i inject current to measure the voltage. the real current into TIA became frequency dependent. input current and output voltage both drop at higher frequencies, so that the transimpedance looks better than the transimpedance got by that output voltage / constant input current (1A AC).
yes, i think i just use method 1 is better.
 

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