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# Balun3Port (Balun, 3-port)

## Balun3Port (Balun, 3-port)

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##### Notes/Equations
1. Balun3Port realizes the ideal transformation between a balanced differential-mode signal and unbalanced, single-ended signals. It can be useful to connect a source to a differentially fed circuit, although it does ignore common-mode effects.
2. Balun3Port realizes the voltage and current transformations given by:
vd = v+ - v-
i+ = -i- = -id
where
vd / id = the differential mode voltage/current at pin d
v+ / i+ = the single line voltage/current at pin +
v- / i- = the single line voltage/current at pin -
See P.R. Gray and R.G. Meyer, "Analysis and Design of Analog Integrated Circuits", Third Edition, John Wiley & Sons, NY, 1993, equations 3.91 & 3.92.
The minus signs in the current definitions are due to the standard definition of currents directed into the Balun3Port component.
3. An equivalent functionality can be realized with a Balun4Port that has the common-mode pin grounded. However, the Balun3Port provides better convergence properties.
4. Balun3Port is bi-directional. When fed at the differential-mode pin, it realizes the transformations:
v+ = -v- = (vd)/2
i+ = -i- = -id
5. Examples of using Balun3Port to convert between (unbalanced) ADS sources and balanced circuits can be found in the ADS examples directory; access these examples from the ADS Main window > File > Example Project.
• RFIC > MixerDiffMode_prj demonstrates the use of Balun4Port to present differential-mode sources (as well as common mode biases) to the RF and LO inputs. It also shows the use of Balun3Port to single-ended (differential-mode) IF output, which is needed to properly calculate the noise figure.
• BehavioralModels > DifferentialModels_prj demonstrates the use of Balun3Port and Balun4Port in conjunction with single-ended System-Data Models in order to create a data-based behavioral model of a differentially fed mixer.
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