Cosmin Iorga, President, NoiseCoupling.com

In mixed-signal applications, sensitive analog circuits are placed on the same die with high-speed digital circuits. The digital switching transients couple through substrate and power distribution to analog circuits, degrading their performance. Various conventional shielding and guard-ring techniques reduce the noise coupling but do not eliminate it. Additional suppression can be achieved through active cancellation. This paper presents the methodology of circuit-level noise-coupling cancellation and two design examples built in 0.13 um CMOS technology. Coupling reduction of 8.8 times has been achieved in a common-source NMOS amplifier, and side-band suppression of 22 dB in a ring oscillator.