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本文给出了一种常用两级低电压CMOS运算放大器的输入级、中间增益级及输出级的原理电路图及它们的主要工作特性。输入级采用了NMOS管和PMOS管并联的互补差分输入对结构,使输入共模电压范围达到全摆幅(rail-to-rail),并采用了成比例的电流镜技术以实现输入级跨导的恒定;中间增益级采用了适合低电压工作的低压宽摆幅共源共栅结构的电流镜负载,提高了输出电阻,进而提高了增益,同时更好的实现了全摆幅特性;输出级采用了高效率的推挽共源极功率放大器,使输出电压摆幅基本上可以达到rail-to-rail;为了保证运放的稳定性与精确性,其基准电流源是采有一个带电流镜负载的差分放大器;为防止运放产生振荡,采用了带调零电阻的密勒补偿技术对运放进行频率补偿。用Hspice软件仿真(因篇幅有限从略)表明了运放较好地达到了设计要求。
This paper presents a common two-stage low-voltage CMOS op amp input stage, intermediate gain stage and output stage of the principle circuit and their main operating characteristics. The input stage incorporates a complementary differential input-pair configuration in parallel with an NMOS transistor and a PMOS transistor to achieve a rail-to-rail input common-mode voltage range with a proportional current mirror technique for input-stage transconductance ; The intermediate gain stage uses a current mirror load of a low-voltage, wide-swing cascode structure suitable for low-voltage operation to improve the output resistance, thereby increasing the gain and better achieving the full swing characteristic; the output stage Using a high efficiency push-pull common-source power amplifier, the output voltage swing can basically achieve rail-to-rail; in order to ensure the stability and accuracy of the op amp, the reference current source is taken with a current mirror Load differential amplifier; In order to prevent operational amplifier oscillation, using zero offset resistance Miller compensation technology to carry out the frequency of op amp compensation. Hspice simulation software (due to limited space omitted) shows that the op amp better meet the design requirements.