Digital OTA with Floating-Inverter Input Stage and Isolation Resistor-Based Frequency Compensation for Ultra-Low Power CT-ΣΔ Modulators

This paper presents a fully differential floating inverter-input digital operational-transconductance-amplifier (FI-DIGOTA) featuring isolation resistor-based frequency compensation. The proposed FI-DIGOTA achieves a DC gain of 59.2 dB, a gain-bandwidth product (GBP) of 50 kHz, and a phase margin (PM) of 47.5 degrees, while operating at an ultra-low (UL) supply voltage of 0.4V. The power consumption of the proposed FI-DIGOTA is 7nW, making it well-suited for energy-constrained applications. A first-order continuous-time Delta-Sigma (CT-Delta-Sigma) modulator utilizing an integrator based on the proposed FI-DIGOTA is proposed as an application example and achieves a signal-to-noise-and-distortion ratio (SNDR) of 44 dB, a spurious-free dynamic range (SFDR) of 55.18 dB, and an effective number of bits (ENOB) of 7.016 bit over a 500 Hz bandwidth at 100 oversampling ratio (OSR).