Substrate noise reduction based on impedance balance using tunable resistances

Substrate noise coupling from digital circuits causes degradation of performance of analog circuits on the same LSI chip. Generally large area on the chip is necessary to reduce the substrate coupling. In this paper, a proposed method eliminates the substrate coupling by extension of the impedance balance control technique which was proposed by the authors. The impedance balance condition on the LSI chip is satisfied by tunable resistances inserted into the substrate contacts. Even if the substrate coupling between two circuits is low (for example, 70 Ω,) the substrate noise coupling was reduced enough on the condition of impedance balance.