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This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. Find sources: "Fontana bridge" – news · newspapers · books · scholar · JSTOR (June 2023)

A Fontana bridge is a type of bridge circuit that implements a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops, implicit in this bridge configuration. This feature allows compensation for parasitic impedance ${\displaystyle Z_{P}}$ connected in parallel with the useful load ${\displaystyle Z_{S}}$, which in turn keeps an excitation current ${\displaystyle I_{S}}$ flowing through the useful load ${\displaystyle Z_{S}}$ independent of the instantaneous value of ${\displaystyle Z_{S}}$. This feature is of great advantage for making electromechanical transducers.

If balance condition:

${\displaystyle Z_{1}Z_{3}=Z_{P}Z_{2}}$

is met, then:

${\displaystyle I_{S}=V_{IN}{\frac {Z_{P}+Z_{1}}{Z_{P}Z_{1}}}}$

The circuit includes two differential amplifiers. The top differential amplifier, whose output is referenced to ground potential, has unitary gain. The bottom differential amplifier, whose output is referenced to ground potential, has ideally infinite gain. Ordinary operational amplifiers can be adopted with limitations in accuracy and bandwidth. The Fontana bridge is also called Compensated Current Injection Circuit. It was originally discovered by Giorgio Fontana, University of Trento, Italy, in 2003 using a symbolic equation solver for Kirchhoff's circuit laws. The bridge details are available in.

References

1. Fontana, Giorgio. "Compensated current injection circuit, theory and applications". Review of Scientific Instruments. 74 (3): 1332–1337. arXiv:physics/0209038. doi:10.1063/1.1535238. ISSN 0034-6748.
2. ArXiv
3. Agarwal, Tarun (2016-08-17). "Different Types of Bridge Circuits and Its Functions". ElProCus - Electronic Projects for Engineering Students. Retrieved 2023-06-28.

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