**4. Discussion**

The CDC based on the IDCD architecture, introduced in [17], has the important characteristic to relay only on digital gates, thus being easily portable among different technological nodes once the fundamental design trade-offs, analysed for the first time in Section 3.1, are taken into account.

Here, we presented a design case, implemented on a low-cost commercial 180 nm-CMOS technology, capable of operating at button-cell supply voltages. Direct comparison with the original implementation of [17] is presented in Table 2. Energy figures are less favourable in the presented design case, as expected, due to the larger minimum feature size of the process used in this work with respect to the case of [17].


**Table 2.** Operative conditions and performance comparison table of IDCD CDCs.

The large difference between the FoM and FoMN values clearly states that, in the current work, distortion effects are much less important than physical noise, while in [17], both distortion and noise contributed to the final resolution of the converter. These aspects confirm the analysis developed in Section 3.1 and give insights into energy efficiency vs. resolution trade-offs of the IDCD-CDC architecture when ported across different CMOS technological nodes.

In conclusion, the IDCD-CDC architecture proves to be a valid solution for capacitive sensor read-out interfaces in the medium/low resolution range. The IDCD-CDC fully exploits the benefits of miniaturization offered by more advanced CMOS technological nodes, while still providing competitive energy figures, even when implemented in lowcost 180 nm CMOS technology. In both cases, compatibility with low-voltage operation is maintained. When looking at evolutions of this architecture, capable of targeting more stringent resolution requirements, the inclusion of additional control circuitry needs to be investigated. Such circuitry should be devoted to the implementation of dynamic techniques for noise reduction and/or noise-shaping mechanisms.

**Author Contributions:** Conceptualization, M.D.; methodology, P.B. and M.P.; software, M.C.; validation, M.C.; formal analysis, M.D., P.B. and M.C.; resources, P.B. and M.P.; data curation, M.D., P.B., M.C. and M.P.; writing—original draft preparation, M.D.; writing—review and editing, M.D., M.C., P.B. and M.P.; supervision, P.B. and M.P.; project administration, M.D. and P.B.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie gran<sup>t</sup> agreemen<sup>t</sup> No. 893544.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data contained in the text.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
