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(Obsolete) Gamma Probe (Closed Form): GPROBE



This element is OBSOLETE and is replaced by the Gamma Probe (Closed Form) (GPROBE2).


Name Description Unit Type Default
ID Element ID Text XF1
Rsense Current sense resistance   0.0001

Parameter Details

Rsense. This value must be nonzero, however it can be made small enough such that the probe circuit may be considered lossless.

Implementation Details

The gamma probe (GPROBE) element is an insertable element that is placed on the input and output pins of active devices. When placed, it is invisible to the circuit so that the through-signal path is not disturbed. This probe calculates the two reflection coefficients for the node into which it is inserted (Gamma 1 looks to the left and Gamma 2 looks to the right). The reflection coefficients themselves can be plotted, but the main thing to view is the STAB_GP measurement, which is the product of the two reflection coefficients. If this product is greater than 1 at any frequency or load (or source pull point), then the device is unstable.

The stability measurements STAB_GP and STAB_GPN and the internal gamma measurements GAM1_GP and GAM2_GP require that the excitation ports (connected to nodes 1 and 2) are specified as part of the measurement. You must also specify the ports connected to the voltage and current sampling terminals of the GPROBE element for these measurements (the measurement requires that ports be placed on the V and I nodes of the GPROBE element).

You should use GPROBE in circuits without feedback across the active devices. If this feedback is present, GPROBEM may provide better accuracy. See “Performing Internal Stability Analysis” for more information on the operation of GPROBE. Implementation details of GPROBEM (GPROBE is analogous) can be found in the document listed in "References" (see Fig.3); this document is available for download from the Cadence® AWR® Knowledge Base (search for GPROBEM).


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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