【摘要】：隨著科學技術的高速發(fā)展,越來越多的領域涉及到微弱信號的檢測與分析。微弱信號通過各類傳感器轉(zhuǎn)換為電學信號,傳感器輸出的電信號通常頻率較低且十分微弱,需要經(jīng)過前置放大器放大輸出。在微弱信號檢測系統(tǒng)中,前置放大器是整個檢測系統(tǒng)的關鍵模塊,這使得低噪聲高增益放大器的研究成為一個重要課題。本文的主要目的是設計一款適用于傳感器輸出信號放大的高增益、低噪聲、輸出無失真的前置放大電路。本文從放大傳感器輸出的微弱信號出發(fā),提出了放大電路的設計指標。通過對常用的集成放大電路優(yōu)缺點分析,提出了使用結型場效應管作為輸入器件設計噪聲性能更高的放大電路方案。在具體的電路設計中使用優(yōu)先考慮噪聲特性的設計方法:先確定滿足噪聲要求的輸入級器件,選定合適的工作點,設計偏置電路,確定有源器件的電路組態(tài),最后設計反饋網(wǎng)絡和補償電路。這種設計方法可以使電路做到噪聲最佳。本次設計的放大電路由兩級放大級聯(lián)構成,由于應用于低頻環(huán)境下,所以兩級之間采用直接耦合方式。整個放大電路主要由輸入級、輸出級、偏置電路、反饋電路和補償電路構成。完成電路整體設計后,使用PSpice軟件對放大電路整體進行電壓增益、瞬態(tài)分析、等效輸入噪聲、共模抑制比等方面的仿真,得出的仿真結果顯示所設計的放大器差模電壓增益為1071倍,上限截止頻率達到了585k Hz,共模抑制比在所要求的工作頻率內(nèi)高于90d B,等效輸入噪聲為納伏級別,滿足了設計要求。為了進一步驗證放大電路的可行性,制作實際電路板,對其進行了小信號輸入-輸出測試和頻率特性測試,實際的測試結果表明放大器能夠無失真地放大低頻微弱信號。
[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.
【學位授予單位】：湖南大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN722.71

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