应用于低频微弱信号检测的前置放大电路设计
发布时间：2018-11-18 20:45
【摘要】：随着科学技术的高速发展,越来越多的领域涉及到微弱信号的检测与分析。微弱信号通过各类传感器转换为电学信号,传感器输出的电信号通常频率较低且十分微弱,需要经过前置放大器放大输出。在微弱信号检测系统中,前置放大器是整个检测系统的关键模块,这使得低噪声高增益放大器的研究成为一个重要课题。本文的主要目的是设计一款适用于传感器输出信号放大的高增益、低噪声、输出无失真的前置放大电路。本文从放大传感器输出的微弱信号出发,提出了放大电路的设计指标。通过对常用的集成放大电路优缺点分析,提出了使用结型场效应管作为输入器件设计噪声性能更高的放大电路方案。在具体的电路设计中使用优先考虑噪声特性的设计方法:先确定满足噪声要求的输入级器件,选定合适的工作点,设计偏置电路,确定有源器件的电路组态,最后设计反馈网络和补偿电路。这种设计方法可以使电路做到噪声最佳。本次设计的放大电路由两级放大级联构成,由于应用于低频环境下,所以两级之间采用直接耦合方式。整个放大电路主要由输入级、输出级、偏置电路、反馈电路和补偿电路构成。完成电路整体设计后,使用PSpice软件对放大电路整体进行电压增益、瞬态分析、等效输入噪声、共模抑制比等方面的仿真,得出的仿真结果显示所设计的放大器差模电压增益为1071倍,上限截止频率达到了585k Hz,共模抑制比在所要求的工作频率内高于90d B,等效输入噪声为纳伏级别,满足了设计要求。为了进一步验证放大电路的可行性,制作实际电路板,对其进行了小信号输入-输出测试和频率特性测试,实际的测试结果表明放大器能够无失真地放大低频微弱信号。
[Abstract]:With the rapid development of science and technology, more and more fields involve weak signal detection and analysis. The weak signal is converted into electrical signal by various sensors. The signal output by the sensor is usually low frequency and very weak, so it needs to be amplified by preamplifier. In the weak signal detection system, the preamplifier is the key module of the whole detection system, which makes the research of low noise and high gain amplifier become an important subject. The main purpose of this paper is to design a preamplifier circuit with high gain, low noise and no distortion. Based on the weak signal output from the amplifier sensor, the design index of the amplifier circuit is presented in this paper. Based on the analysis of the advantages and disadvantages of common integrated amplifier circuits, a scheme of using junction FET as input devices to design amplifiers with higher noise performance is proposed. In the specific circuit design, the design method of priority noise characteristic is used: first, the input level device that meets the noise requirement is determined, the suitable working point is selected, the bias circuit is designed, and the circuit configuration of the active device is determined. Finally, the feedback network and compensation circuit are designed. This design method can make the circuit noise optimal. The amplifier circuit is composed of two stage amplifier cascade. Because it is used in low frequency environment, direct coupling is adopted between the two stages. The amplifier circuit consists of input stage, output stage, bias circuit, feedback circuit and compensation circuit. After the overall design of the circuit is completed, the voltage gain, transient analysis, equivalent input noise and common-mode rejection ratio of the amplifier circuit are simulated by using PSpice software. The simulation results show that the differential mode voltage gain of the designed amplifier is 1071 times, the upper cutoff frequency reaches 585k Hz, common mode rejection ratio is higher than 90 dB in the required operating frequency, and the equivalent input noise is nanovolt level. Meet the design requirements. In order to further verify the feasibility of the amplifier circuit, the practical circuit board is fabricated, and the small signal input-output test and the frequency characteristic test are carried out. The actual test results show that the amplifier can amplify the low frequency weak signal without distortion.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN722.71
[Abstract]:With the rapid development of science and technology, more and more fields involve weak signal detection and analysis. The weak signal is converted into electrical signal by various sensors. The signal output by the sensor is usually low frequency and very weak, so it needs to be amplified by preamplifier. In the weak signal detection system, the preamplifier is the key module of the whole detection system, which makes the research of low noise and high gain amplifier become an important subject. The main purpose of this paper is to design a preamplifier circuit with high gain, low noise and no distortion. Based on the weak signal output from the amplifier sensor, the design index of the amplifier circuit is presented in this paper. Based on the analysis of the advantages and disadvantages of common integrated amplifier circuits, a scheme of using junction FET as input devices to design amplifiers with higher noise performance is proposed. In the specific circuit design, the design method of priority noise characteristic is used: first, the input level device that meets the noise requirement is determined, the suitable working point is selected, the bias circuit is designed, and the circuit configuration of the active device is determined. Finally, the feedback network and compensation circuit are designed. This design method can make the circuit noise optimal. The amplifier circuit is composed of two stage amplifier cascade. Because it is used in low frequency environment, direct coupling is adopted between the two stages. The amplifier circuit consists of input stage, output stage, bias circuit, feedback circuit and compensation circuit. After the overall design of the circuit is completed, the voltage gain, transient analysis, equivalent input noise and common-mode rejection ratio of the amplifier circuit are simulated by using PSpice software. The simulation results show that the differential mode voltage gain of the designed amplifier is 1071 times, the upper cutoff frequency reaches 585k Hz, common mode rejection ratio is higher than 90 dB in the required operating frequency, and the equivalent input noise is nanovolt level. Meet the design requirements. In order to further verify the feasibility of the amplifier circuit, the practical circuit board is fabricated, and the small signal input-output test and the frequency characteristic test are carried out. The actual test results show that the amplifier can amplify the low frequency weak signal without distortion.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN722.71
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