Design of a 4th-Order Feed-Forward-Compensated Operational Amplifier for Multi-GHz Sampling Frequency Continuous-Time Bandpass Sigma-Delta Modulators

Abstract : This work presents a 4 th-order multi-stage, multi-path, feed-forward-compensated operational amplifier in 65 nm CMOS technology. It is designed to meet the requirements of a continuous-time bandpass Σ∆ modulator with multi-GHz sampling frequency. The designed amplifier is modular with each stage implemented based on a unit differential amplifier block and it meets its targets with smart placement of poles and zeros. The amplifier is simulated under the loading condition of a single-amplifier resonator which is in turn part of a 6 th-order Σ∆ modulator. The unloaded amplifier reaches a unity-gain-frequency of 38.29 GHz and a DC gain of 58 dB. With a parallel load of 440 fF and 300 Ω, representing the maximum load, the op-amp, including common-mode and biasing circuits, consumes a total of 18.98 mA from a supply voltage of 1.2 V. It is unconditionally stable with a phase margin of 54 • and has gains of 35 dB and 23 dB at 1 GHz and 2 GHz respectively.
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Submitted on : Monday, June 3, 2019 - 10:27:01 AM
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Fikre Tsigabu Gebreyohannes, Marie-Minerve Louërat, Hassan Aboushady. Design of a 4th-Order Feed-Forward-Compensated Operational Amplifier for Multi-GHz Sampling Frequency Continuous-Time Bandpass Sigma-Delta Modulators. 2019 IEEE International Symposium on Circuits and Systems (ISCAS), May 2019, Sapporo, Japan. ⟨10.1109/ISCAS.2019.8702147⟩. ⟨hal-02145589⟩

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