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--- vlsi:analog_impedance_sim [23/04/2013 23:09]
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-====== Node impedance simulation ======
-== Contents ==
-   * Introduction
-   * Procedure
-   * Simulation example
-**Keywords:**
-===== Introduction =====
-===== Procedure =====
-Basta attaccare un **idc** source al nodo di cui si vuole misurare l'impedenza di uscita e mettere AC=1. Poi analisi
-in frequenza e la tensione in Volt che mi esce e' anche il valore della resistenza in ohm (essendo R = V/I con I=1A)
- apply a test current Iout
-and watch the effect on the output voltage (or vice versa).
-Since Zout = Vout/Iout and Iout (ac) == 1, the magnitude of the output voltage corresponds indeed with the output impedance of your circuit.
-In general you have to ensure that your device has the correct DC bias.  The output resistance given by AC analysis is dependent on the bias.   In general, you add a DC source (if needed for biasing) and then perform an AC analysis to get output impedance.
-Place this source across the nodes where you want to measure the impedance. The Value attribute of the Current Source should be defined as 'AC 1'. This provides a 1A AC current source for AC analysis. Enter AC analysis.
-Since the current is 1A, the voltage across the current source is equivalent to the impedance, so this expression will produce the impedance plot.
-===== Simulation example =====
-Esempio: diode connected NMOS
-{{:vlsi:impedance_sim_schematic.png}}
-{{:vlsi:impedance_sim_idc_settings.png}}
-{{:vlsi:impedance_ade_settings.png}}
-{{:vlsi:impedance_sim_dc_op.png}}
-gm = 25.8 uS, gds <nowiki> << </nowiki> gm
-/gm = 38.76 kohm
-{{:vlsi:impedance_sim_ac_analysis.png}}
-Vg = 38.76 kV poi su 1 A sono proprio 38.76 kΩ