1.2 Increasing the gain in LNA 18dB to 24 dB adds more external noise to the signal (modulates it) / digital gain from 1 to 6dB increases signal / changing VCA attenuator does not change amplitude Do you mean that an LNA gain increase amplifies the artifact, or just the random noise? The artifact amplitude does not change with VCAT change? 0-40dB? This implies the artifact is introduces between the VCAT and the PGA. Does increasing the PGA gain from 24dB to 30dB amplify the artifact? Please power down LNA, VCAT and PGA in that order until the artifact disappears, reg 0x35. The layout seems ok, it would be good if you could probe the AVDD-3.3V supply for the artifact. This supplies the PGA.
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