1-bit digital tuning of continuous-time filter by the use of unstable sigma-delta modulation

A 1-bit digital frequency tuning technique for continuous-time filter is presented. Unstable sigma-delta modulation is used. A 1-bit digital tuning signal can be generated by detecting the stability of a highly unstable sigma-delta modulation loop. Simulations on a third-order and a fourth-order sigma-delta modulation loops show up to 2% tuning accuracy that can be reached with the 1-bit tuning technique.