Preamplifier simulation test scheme in extremely weak current signal detection circuit

Very weak quasi-DC current signal measurement technology is widely used in the development of precision instrumentation.

The preamplifier is the core, which determines the noise level and response time constant of the system. In the simulation study of the preamplifier, the electrical noise model of the preamplifier was constructed by the resistance direct feedback method and the "T" type resistor network feedback method, and the performance parameters of the preamplifier under various conditions were obtained. The simulation results show that the signal-to-noise ratio of the system is inversely proportional to the equivalent capacitance value of the sensor, and proportional to the value of the feedback capacitance, and it cannot be generally considered which method is better than the direct resistance feedback method or the "T" type resistance network feedback method. Choose the appropriate feedback form according to the specific situation. The simulation results can provide a reference for the design of the preamplifier in the extremely weak current signal detector.

In the field of space exploration technology, nuclear detection technology and other instrumentation research fields, it is necessary to use a detection circuit that accurately measures extremely weak quasi-DC current signals. The preamplifier is the core of the circuit and determines the noise level and response time constant of the system. . According to the Fris formula, the noise figure of the preamplifier has the greatest influence on the total noise figure of the amplifier. Therefore, the preamplifier is required to have low noise, stable gain, accuracy and strong anti-interference ability. With the continuous development of low-noise operational amplifier technology, it has become an important development trend to directly select low-noise operational amplifiers to design sensor preamplifiers.” The application of high-performance operational amplifiers greatly simplifies the design and adjustment of low-noise circuits. The task of designing a preamplifier is to optimize the noise characteristics of the amplifier under the conditions of a given sensor, output signal amplitude, sensor internal resistance, sensor equivalent capacitance, amplifier gain, impedance and response characteristics, that is, the output signal has The best signal-to-noise ratio.

The ATA-5620 preamplifier effectively reduces the area occupied by the capacitor in the amplifier, but compared with the traditional circuit, the noise is larger, and it has a good performance in terms of gain and input noise.

Bandwidth: Bandwidth (-3dB) 1kHz~100MHz

Voltage: Maximum output voltage 2Vp-p

Gain multiple: voltage gain 60dB

Ultra low noise power supply

In short, the design of preamplifiers for weak signal measurement based on high-performance operational amplifiers is very complicated, involving many theoretical and technical issues, and many issues are interrelated and constrained. In specific applications, it is necessary to find a compromise point according to the actual situation to balance various parameters and make the design plan the best.

The electrical noise model of the two feedback methods of the preamplifier for the measurement of the extremely weak DC current signal of the operational amplifier simulates the performance parameters of the preamplifier in various situations. The simulation results show that the signal-to-noise ratio of the system is directly proportional to the feedback capacitance and inversely proportional to the equivalent capacitance value of the sensor, and it cannot be generally considered which method is better for the direct resistance feedback method and the "T" type resistance network feedback method. Choose the appropriate form of feedback for the specific situation. The simulation results can provide a reference for the design of preamplifiers in weak signal measurement based on high-performance operational amplifiers.