Comment on “Compact, High-Q, and Low-Current Dissipation CMOS Differential Active Inductor”

In a recent letter [ibid., vol. 18, no. 10, pp. 683??685, Oct. 2008], C.L. Ler et al. present a CMOS differential active inductor (DAI) based on the single transistor source degenerated architecture proposed by those authors in ibid., vol. 44, no. 3, pp. 196??197, Jan. 2008. The aim of this Comment is to reveal the general configurations and circuit equivalences which the results in the Oct 2008 paper are based on and to prove that the active inductor does not fit to the term gyrator mentioned in that paper. In this regard, two observations are proposed. The first one is that both circuits can be derived from given general topologies using capacitors for Z(s). The second observation is that the series connection shown here in Fig. 2(a) is equivalent to the series-parallel circuit in Fig. 2(b) which for Z(s) = 1/sC gives the results reported in the two papers referenced.