一种适合宽范围电容负载的三级运放

结合精确度和稳定性的要求提出了一种适合宽范围电容负载的CMOS运放.在多径嵌套式密勒补偿结构中加入一个抑制电容,得到适合各种电容负载的稳定性.为了证实稳定性的提高,对该结构进行了理论分析并计算得出数学表达式.基于这种新的频率补偿结构,利用CMOS 0.7μm工艺模型设计了样品芯片.测试结果表明该运放可以驱动从100 pF到100μF负载电容,直流增益为90dB,最小相位裕度为26°.该运放在100 pF负载情况下单位增益带宽为1 MHz,抑制电容仅为18 pF.

A Three-Stage Operational Amplifier for a Wide Range of Capacitive Loads

It is presented a three-stage CMOS operational amplifier (opamp) that meets the requirement of both accuracy and stability for a wide range of capacitive loads. A so-called quenching capacitor is added to multipath nested Miller compensation (MNMC) topology to obtain stability for a variety of capacitive loads. Theoretical analysis and calculation are carried out to prove the stability improvement. A prototype of this frequency compensation scheme is implemented in 0.7 μm CMOS process. The measurement results show that the amplifier is able to drive capacitive loads ranging from 100 pF to 100 μF with a gain of 90 dB and a minimum phase margin of 26°. The amplifier has a unity-gain bandwidth of 1 MHz for 100 pF capacitive load. The quenching capacitance is only 18 pF.