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Design Notes

"Tweaking" MMIC Capacitor Values after EM Simulation


This project shows how to extract a MMIC capacitor for EM simulation, such that its value can then be tuned without re-extraction.


EM Extraction allows MMIC designers to conveniently verify the performance of collections of elements using an EM simulator.  However, unless capacitors are not included in the extraction, there is no way to take advantage of the EM results, AND quickly tune or optimize the capacitor values. 

This project shows a technique for adding an ideal lumped capacitor in parallel with an extracted MMIC capacitor, so that its value can be tuned or optimized without changing its size and re-extracting (i.e. performing another EM simulation).  Once the correct value is found, the ideal capacitor can be removed, and the original capacitor size can be adjusted as needed, so that a new extraction can verify the desired performance has been acheived.


The Microwave Office PDK used in this project is the AWR_MESFET which provides an AXIEM specific STACKUP called "Thick". 

Modeling and Simulation

The schematic "Series_Port_TC"  consists of a series capacitor between two plated lines.  Each plated line is split into two parts.  The sections closest to the capacitor are extracted along with the capacitor itself.  There is also an additional set of elements in the box named "Tweakers": an ideal lumped capacitor connected between two MLEF elements.  The MLEF elements are not used as electrical models.  They act as place-holders for the capacitor's terminals in the layout.  One of them is placed on the capacitor's top metal, and the other on the bottom metal, and an extraction port is attached to each of them.  The extraction ports are specified as members of the same "Series" type port group.

After extraction the capacitor connected between the MLEFs in the schematic can be adjusted, and its value will effectively add to the capacitance of the extracted cap.  Tune this capacitor to see its effect.

Simulation Plots

The equivalent capacitance and s-parameters for the "Series_Port_TC" schematic are shown in the "Equivalent Capacitance" and "S Parameters" graphs, respectively.  You can tune the capacitance to see how it affects the results without

Schematic - Series_Port_TC

Schematic - Explicit_Ground_TC

EM Structure - EM_Extract_Doc_series

EM Structure - EM_Extract_Doc_explict_ground

Graph - S Parameters

Graph - Equivalent Capacitance