Rearch And Desigen Of CMOS Fully Differential Low Noise Opamp

Opamps are widely used in many fields nowadays such as A/D and D/A converter, active filter and AGC. All kinds of different opamps appear for special applications.The thesis introduces a low noise opamp which can be used in weak signal detection system or high quality audio system in detail. The opamp is implemented with 0.18um CMOS technology. The power supply is 1.8V. The design of main circuit is finished by the purpose of reducing input reference noise. The first stage is a cascode circuit, and the second stage is a common source amplifier, considering both internal device noise and external power noise's influence. For getting proper DC operation point, a common feedback circuit based on negative feedback theory is designed. At last, important parameters such as open—loop gain, phase margin and input reference noise are analyzed and deduced. The simulation is finished by cadence's IC5033 in SUN workstation. The simulation shows the input reference noise at 1KHz is only about5.1 .It's quite a good result.