| With rapid development of science and technology, more and more fields relate to detection and analysis of weak signal. Generally speaking, aims convert non-electrical to electrical signal by sensors. However, electrical signals output from sensors are so weak that amplification by preamplifier is needed. In a system for detecting weak signal, pre-amplifier is the key module of the whole detection system. Hence, development of amplifier with low-noise and high-gain is of importantance. The purpose of this paper is to design a suitable pre-amplifier circuit for amplifying signal from sensors.Based on the weak signal output from amplification sensor, this paper puts forward the design index of the amplifying circuit. By comparing advantages and disadvantages of the commonly used integrated amplifying circuit, this paper comes up with a scheme of amplifying circuit, and JFETs are used to improve noise performance. In the concrete circuit design, the method of the priority of noise characteristics is used. First of all, determine the input device that can satisfy the requirement of noise and select the appropriate working parameters. Then, biasing circuit and circuit configuration of active device are designed. At last, feedback network and compensating circuit included. This design configuration can reduce noise. The design of the amplifying circuit consists of two stages of amplifying cascades. Due to application in low-frequency fields, direct coupled mode is used between the two stages. The entire amplifying circuit is mainly composed of input stage, output stage, biasing circuit, feedback circuit and compensating circuit.After completion of the whole circuit design, PS pice simulation software is used to simulate the voltage gain, the transient analysis, the equivalent input noise, common mode rejection ratio and so on. It is concluded that the simulation results show that the designed amplifier’s differential mode voltage gain is 1071, upper cut-off frequency reaches 585 k Hz, common mode rejection ratio exceeds 90 d B within the required working frequency and that the equivalent input noise is the n V level. What’s more, in order to further verify the feasibility of the design ed circuit, the actual circuit board is made to test on small signal input-output and frequency characteristic and the actual test results show that the amplifying circuit can amplify weak signals with low frequency without distortion. |
