Graduation date: 2007The substrate noise injected by a stepped buffer circuit into two single-ended 1.5GHz low noise amplifiers is examined for a heavily doped 0.25µm CMOS process. The difference in the LNA noise rejection is characterized as a function of the size and placement of substrate contacts. The use of a resistive model for the substrate, and SPICE models for the interconnect and passive device parasitics give good correlation between the measured and simulated results. A reduction of 2-12dB is achieved for the intermodulation products, with larger substrate contacts. It is shown that large ground taps placed in close proximity to the input transistor are most effective in suppressing the IM levels.A detailed examination of the noise injection mechanisms in a stepped buffer shows that the injected noise is a strong function of the layout of the buffer interconnects. Proposed methods to reduce the injected noise result in improvements of 9-11dB.