信号检测与放大（Signal detection and amplification）.doc

信号检测与放大（Signal detection and amplification） The basic structure of the circuit The signal generated by a biosensor is usually a weak signal with a low frequency, which can detect different plant physiological parameters and may obtain a voltage or current signal. For the current signal, the current signal should be converted into a voltage signal first, by amplifying the amplification of the circuit, and finally using the low-pass filter to filter out the high-frequency noise mixed in the signal. The overall structure of the preamplifier circuit is shown in figure 1. Considering that the signal generated by the sensor is very weak, it is easy to be polluted by the noise, so the amplifying circuit selects the instrument amplifier structure. The instrument amplifier has the differential structure, which has a strong inhibitory effect on the common mode noise, and has high input impedance and small output impedance, which is very suitable for amplifying the weak signal. In order to make the output voltage drop at a faster speed in the high frequency band, and improve the ability of the low-pass filter to filter out the noise, the second-order low-pass filter is selected. The schematic diagram of the preamplifier circuit is shown in figure 2. Biological sensor produced by biological signal usually has a large dynamic range, reach several orders of magnitude, schematic diagram of R2 as a variable resistance, through changing the value of R2, can change the magnification instrumentation amplifier, thereby adapting to different sizes of weak signal amplification. 3. Suppression and shielding of noise In the process of weak signal detection, noise suppression and shielding is crucial, because the signal is weak, the vulnerable to noise pollution, the noise of main noise produced by environmental noise, circuit components themselves and the power of noise, power frequency for this in noise suppression and shielding to consider these factors. 3.1 selection of components In th