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Oscillator Open-Loop Element Differential Excitation: OSCTEST2

Symbol

Summary

OSCTEST2 is a type of directional coupler useful for loop gain computation in oscillators. It presents a short circuit everywhere except at a specified frequency (or range of frequencies) near the intended frequency of oscillation. OSCTEST2 is a more general form of OSCTEST, to which it degenerates when terminals 5 and 6 are grounded. It is more general than OSCTEST in the sense that it may be used to compute open-loop gain in differential oscillators.

Topology

Parameters

Name Description Unit Type Default
ID Element ID Text OD1
FC Loop frequency Ghz _FREQ*1e-9
*Z0 Port impedance ohm 50

* indicates a secondary Parameter

Parameter Details

The easiest way to specify FC is to utilize the built-in variable _FREQ (for linear simulations) or _FREQH1 (for large-signal simulations). Note that _FREQ is a number (or array of numbers) equal to the project frequency in Hz, so if FC is specified in user units (GHz by default) the FC entry must be scaled appropriately (_FREQ*1e-9). If Schematic Dependent Parameters Use Base Units is selected on the Project Options dialog box Schematic/Diagrams tab, no scaling is necessary since parameter FC will automatically be calculated in base (MKS) units.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

Recommendations for Use

To compute loop gain, break the loop so that the large arrow points in the direction of forward gain, as in the following figure.

The S21 parameter of the circuit should equal the open-loop S21 of the GAIN stage.

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