Performances Evaluation of On-chip Large-Size Tapped Transformer for MEMS applications
(2020) IEEE Transactions on Instrumentation and Measurement — Vol. 69, n° 9, p. 7051-7060 (2020)
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- Abstract
- This paper aims at providing a better behavior understanding and performance evaluation of a large-size passive on-chip tapped transformer when used as a transducer in low-frequency integrated microsystems [30–300 kHz]. Thus, a CMOS-based 1:1 transformer, consisting of 70 turns of 1.6 μm-wide top-level metal spaced by 0.6 μm and with a total length of 1.7 mm, has been investigated and tested. The spatial separation between the two transformer windings was set to 70 μm. An electrical equivalent lumped model has been extracted through an exhaustive specific measurement procedure. The model is useful to simulate and evaluate the voltage transformation ratio between the two transformer windings. The effects of parasitics and imperfect coupling between transformer windings and through the silicon substrate are outlined from the circuit point of view. We report a magnetic coupling coefficient which does not exceed k=0.15, with a voltage transformation ratio of about 0.39 around the resonance frequency of ~5.3 MHz, when the secondary is unloaded. It has been proved that the interwindings capacitance introduced by close conductors of each winding, evaluated to 13 pF, assures the most important role in the power transfer. This study has shown that by optimizing properly the transformer realization and limiting some parasitics elements, the inductive and capacitive links could both play a key role in MEMS transducers through tapped transformers operation around hundred kHz frequencies.
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Tounsi, F., Flandre, D., Rufer, L., & Francis, L. (2020). Performances Evaluation of On-chip Large-Size Tapped Transformer for MEMS applications. IEEE Transactions on Instrumentation and Measurement, 69(9), 7051-7060. https://doi.org/10.1109/TIM.2020.2974409 (Original work published 2020)