微弱信号探测中信号幅度很宽会导致幅度小的信号分辨率低,结合脉冲振幅调制叶绿素光合活性荧光仪中不同强度光源激发下光电倍增管光电流响应,采用多路选择开关D5201G芯片选择I/V转换电路中不同阻值的反馈电阻实现了对输入信号可变增益放大。0~118 mV以下输入信号的理论增益值最高可达28.25 dB,同时输入信号的电压幅值最高可达11.11 V。

Detection of weak signals is often encountered in greate range of amplitude, so it would lead to small signal low resolution.Pulse amplitude modulated chlorophyll fluorescence in photosynthetic activity of different intensity excitation light photocurrent response by photomultiplier tube is intnoduced in this paper. Multiple selector switch D5201G chip and HC 374 are used to select different values of feedback resistor in I/V conversion which work as a variable gain amplifier. The theoretical gain of input signal under 0~118 mV is up to 28.25 dB, while the input signal amplitude would be up to 11.11 V.