Design of current-mode companding √-domain dynamic circuits

In this paper, the strong inversion MOS analogue of the log-domain principle, or dynamic translinear principle, is derived. The resulting class of √-domain circuits is based on the square law describing the large-signal behaviour of the MOS transistor in strong inversion. An inherent characteristic of √-domain filters is instantaneous companding, which is especially interesting for low-voltage applications. The design of a current-controlled two-integrator oscillator, based on the √-domain principle, is described. The oscillator was realised in a 1.6 μm n-well CMOS process, for a supply voltage of 3.3 V. Measurements show a total harmonic distortion of -42 dB and linear frequency tunability across 1.3 decades