Current-mode multi-path excess loop delay compensation for GHz sampling CT ΣΔ ADCs.

This paper proposes both system-level and circuit-level solutions of a current-mode multi-path excess loop delay (ELD) compensation technique for continuous-time (CT) ΣΔ ADCs with multi-bit quantization and several GHz sampling rate. Thanks to the proposed solutions, the amplifier of the loop filter is not in the fast feedback (FB) loop; the delay of the pre-amplifier of the comparator is removed; and the effective regeneration time of the comparator latch is maximized. The proposed novelties enable CT ΣΔ ADCs with wide signal bandwidth and improved power efficiency. Extensive transistor-level simulations demonstrate their effectiveness and robustness. This work validates the proposed methods by transistor level design and simulations of an 8.4 GHz MASH ΣΔ ADC achieving an SNDR of 71 dB in a signal band of 600 MHz. This shows that our proposed solutions enable power-efficient multi-GHz ΣΔ ADC applications.