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Gamma Probe (Closed Form): GPROBE2



GPROBE2 establishes a reference plane where it is inserted into the signal path, and offers a means of determining the reflection coefficients required for internal stability measurements. It otherwise acts like a short circuit, so it does not affect the behavior or layout of the circuit in any way.


Name Description Unit Type Default
ID Element ID Text GP1

Implementation Details

The gamma probe (GPROBE2) element is an insertable element that should be connected in series with the input and output pins of active devices in multi-stage circuits. When connected, it is invisible to the circuit so that the through-signal path is not disturbed. This probe calculates the two reflection coefficients at the reference plane where it is inserted ("looking out" of each of its own nodes). The reflection coefficients themselves can be plotted, but the primary measurement to view is the STAB_GP2, which is a function of the product of the two reflection coefficients. If this measurement is greater than 1 at any frequency or load (or source pull point), then the circuit may be unstable. See “Performing Internal Stability Analysis” for more information on the operation and use of GPROBE2, and internal stability analysis in general.

NOTE: The GPROBE and GPROBEM elements are now obsolete and should be replaced with the GPROBE2 element. The new approach is much more efficient as no new ports are needed in the schematic.


This element uses a special layout cell for a short circuit. The layout cell allows the elements connected on either side of the element to look through this element. For example, when a MLIN is hooked to a TFCM (capacitor) model and the project has bridge code configured, the line draws the proper interconnect between the line and the cap. If this element is placed between the line and the cap, the layout still draws the same.

You typically do not assign artwork cells to these items.


[1] C. Campbell and S. Brown "Modified S-Probe Circuit Element for Stability Analysis" (white paper)

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