A 20-nW 0.25-V Inverter-Based Asynchronous Delta-Sigma Modulator in 130-nm Digital CMOS Process. - Gustavo Della Colletta; Luis Henrique de Carvalho Ferreira; Sameer R. Sonkusale; Giseli V. Rocha (IEEE Trans. Very Large Scale Integr. Syst., 2017)