Σ-ΔA/D转换器中电压放大型运放的高线性度设计

Low Distortion Design of a Class AB Voltage-Mode Operational Amplifier for Σ-Δ Analog-to-Digital Converters

高阶、高精度是当前Σ-Δ调制器的设计趋势,随着系统结构越来越复杂,带内量化噪声的噪声背景逐渐降低,已不再成为制约调制器精度的主要瓶颈。整个系统的线性失真度对调制器最终精度的影响越来越大,甚至成为决定因素。为提高Σ-Δ调制器的线性度,对运算放大器这一主要非线性源进行了深入的分析,并提出若干优化方案。最后,通过一个三阶单环Σ-Δ调制器结构进行了仿真验证。采用电压放大、AB类输出的运算放大器结构,大大减小了系统功耗。

There is a tendency in the design of Σ-Δ modulators for higher order and precision.As the system architecture becomes more and more complicated,the noise floor in the signal band is getting lower.However,the distortion in the modulator becomes the decisive factor.In order to increase the linearity of the modulator,a careful study is made on the operational amplifier,one of the most important nonlinear sources,and a number of methods for optimization are proposed,which have been validated by simulation of a 3rd-order single-loop Σ-Δ modulator.In the design,a class AB voltage-mode operational amplifier is used to reduce power consumption of the system.