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Efficient sampling of the reference leg noise within a bilinear switched capacitor ΣΔ ADC is presented, resulting in improved thermal noise performance. Whenever a transition occurs in the feedback of a ΣΔ ADC, implemented using bilinear integrators, zero charge is transferred from the reference leg. Consequently the average noise power added by the reference leg can be reduced substantially if the reference leg is only sampled when there is a corresponding charge transfer. For mid-scale inputs, the sampled noise from the reference leg is reduced by more than 6 dB.
Date of Publication: 23 Jan 2003