This patent describes a method for varying the amplitude and frequency of power supply oscillations produced by content addressable memories or other critical circuits using BIST. Supply oscillations are produced by performing noisy (high switching activity—high current demand) searches followed by quiet (low switching activity—low current demand) searches. The amplitude and frequency of oscillations can be varied by changing the number of noisy and quiet searches e.g. pattern 1-noisy quiet, noisy, quiet; pattern 2-noisy, noisy, quiet, noisy, noisy, quiet, etc. By going through different patterns the current demand from the CAM macro increases the likelihood of producing worst—case noise and enables testing of CAM operation as well as surrounding circuitry in these noisy conditions.