A High Current-Efficiency Rail-to-Rail Class-AB Op-Amp With Dual-Loop Control

This brief presents a high current-efficiency rail-to-rail class-AB op-amp with dual-loop control. Based on the conventional folded cascode op-amp with gain-boost, a dual-loop control strategy consisting of a gain-boost loop and an adaptive output stage current control loop is proposed to achieve bidirectional large load driving capability and high DC gain. Furthermore, the adaptive output stage current control loop achieves class-AB operation with symmetric separate signal paths to the output transistors and high reconfigurability. In addition, the implementation of the constant transconductance (<inline-formula> <tex-math notation="LaTeX">$\text{g}_{\mathrm{ m}}$ </tex-math></inline-formula>) rail-to-rail input and slew rate (SR) enhancement circuit is adopted to widen the input voltage range and improve the large-signal transient response. The proposed op-amp is fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 5 V CMOS process with an active area of about 0.25*0.27 mm2. Measured results show the proposed op-amp achieves over 122 dB DC gain, 1 MHz gain-bandwidth, and 2.1 V/<inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> SR under bidirectional load conditions (100pF and 10k<inline-formula> <tex-math notation="LaTeX">$\boldsymbol{\Omega }$ </tex-math></inline-formula>). At 1.5 V and 5.5 V supplies, positive current-efficiency (CE+) are 15 and 1780, negative current-efficiency (CE−) are 37 and 1658, power consumptions are 59.2 <inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> and 225.5 <inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula>, respectively.