Active substrate noise suppression in mixed-signal circuits using on-chip driven guard rings

This paper presents an active substrate noise suppression circuit using a pair of concentric guard rings. The outer guard ring senses the substrate noise, which is inverted and amplified by a SiGe circuit. This on-chip amplifier drives the inner guard ring such that efficient noise cancellation is achieved. A ring oscillator is used to sense the residual substrate noise. The measured noise suppression bandwidth is as high as 400 MHz.