| Nowadays,the analog integrated circuit plays a vital role in the semiconductor industry,and the operational amplifier becomes the fundamental and important module of the analog circuit system.With the continuous advances in the integrated circuit technology and related industries,the complexity of circuit systems has been constantly increased,which leads to the rising industry requirements for operational amplifiers,as well as the using of some operational amplifiers with exceptional performance.Since the operational amplifier is quite sensitive to weak external signals,it would cause serious interference in the output signal of the operational amplifier when the magnitude of noise reaches a certain value.Therefore,it is critical to improve the noise characteristics of the amplifier.At the same time,the Op Amp is also sensitive to EMI signals.A high frequency EMI signal being coupled to input stage would cause DC offset at the output signal.In consequence,the study of low noise with EMI protection has far-reaching significance.On the basis of this research background,the article focuses on the main principle and design method of low noise Op Amp with EMI protection.In the first place,this article briefly introduces the trade-off relationship between the sense of the various technical indicators of the Op Amp.Next,the writer analyzes the theoretical basis of noise in the circuit system and the reason for EMI sensitivity.Then,it focuses on the methodology and the design of main circuit structure of the Op Amp which based on the complementary bipolar technology with noise advantage.The bias circuit of this circuit structure uses a cross-coupled PTAT current source as a current reference.The input stage uses the differential pair structure,as the gain of this circuit could be raised.Also,the input bias current and noise voltage are reduced with the help of using the bias current elimination technology.Besides,the RC low pass filter is inserted before the input transistor which eliminate the high frequency EMI signal.As for the intermediate stage,two differential pair complementary outputs with current mirror are applied,which loads to drive the base of the output transistor.In addition,the buffer output stage employs class-AB structure method in order to meet the rail-to-rail output requirements and improve the drive capability of the Op Amp,while using the translinear loop to control the quiescent current.At length,the frequency compensation technology is performed based on the main structure of the Op Amp in order to reach the requirement of the stability of this circuit.The low noise operational amplifier with EMI protection proposed in this article is based on the Zhongke Yuxin WC40 S bipolar process.In this study,the author simulates circuits by using cadence's spectre,and also completes the design of circuit layout.The final simulation result shows that the equivalent input noise voltage density of the circuit proposed is 6.46 n V/?Hz at 1 k Hz and the input offset voltage is 1.501?V.Additionally,at low frequency,the open loop gain is 114.8 d B and CMRR is 169.2d B.Furthermore,the GBW is 3.993 MHz.Also,the EMIRR at 1 GHz is 96.84 d B.In summary,the technical indicators above prove that the low noise operational amplifier with the EMI protection reach the scheduled requirements. |
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