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# Balun4Port (Balun, 4-port)

## Balun4Port (Balun, 4-port)

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##### Notes/Equations
1. Balun4Port realizes the ideal transformation between balanced (differential- and common-mode) signals and unbalanced (single-ended) signals. It can be used to connect sources to a differentially fed circuit, particularly when modeling common-mode effects are important.
2. Balun4Port realizes voltage and current transformations given by:
vd = v+ - v-
vc = (v+ + v-)/2
id = -(i+ -i-)/2
ic = -(i+ + i-)
where
vd/id = differential mode voltage/current at pin d
vc/ic = common mode voltage/current at pin c
v+/i+ = single line voltage/current at pin +
v-/i- = 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 and 3.92.
The minus signs in the current definitions are due to the standard definition of currents directed into the Balun4Port component.
3. Balun4Port is bi-directional. It converts common/differential-mode signals into two single-ended signals, as well as converting two single-ended signals into common/differential mode signals.
4. If common-mode effects are not desired, Balun3Port provides an equivalent, but numerically more robust, result as grounding the common-mode pin of Balun4Port.
5. Examples of using Balun4Port 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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