高精度电流采样电路设计

Design of high-precision current sampling circuit

设计了一种应用于H桥电机驱动芯片的高精度电流采样电路。提出了一种特殊的电流镜架构,将多个镜像管串联、采样管并联连接,增大了镜像管整体的栅长与采样管的栅宽,在满足版图匹配性的前提下,能够有效地抑制沟道长度调制效应,提高电流镜的精度。另一方面,通过一个高性能的折叠共源共栅(Cascode)误差放大器对电流镜架构进行钳位,并在该误差放大器中设计了一个修调模块降低失调,能够在较大采样比例下得到较好的精度。在输出端采用了Cascode电流镜可实现电机驱动芯片双相或者三相的电流采样。采用0.18μm BCD工艺进行设计与仿真,仿真结果表明:所提出的电流采样电路在采样比例为1︰1000下最高可达到99.19%的精度。

A high-precision current sampling circuit applied to H-bridge motor driver chip is designed.A special current mirror architecture is proposed,which connects multiple mirror tubes in series and sampling tubes in parallel to increase the overall gate length of the mirror tube and gate width of the sampling tube,and effectively suppress the channel length modulation effect and improve the precision of the current mirror on the premise of satisfying the layout matching.On the other hand,a high performance folded-cascode error amplifier is used to clamp the current mirror structure,and a modification module is designed in this error amplifier to reduce misalignment,which can obtain better precision in a larger sampling ratio.Cascode current mirror is used at the output end to realize two-phase or three-phase current sampling of the motor driver chip.The 0.18μm BCD process is used for design and simulation.Simulation results show that the proposed current sampling circuit can achieve 99.19%precision at the sampling ratio of 1:1000.