在用微机来处理人体生理信号时,需将低通滤波器的截止频率从5Hz 到3KHz 分成多档。为此我们设计了一个程控有源低通滤波器,现介绍如下:图1为该程控有源低通滤波器的原理图。为使通带内幅频曲线平直,我们选用伯特沃渐压控电压源型二阶滤甚波器。有源滤波器的增益选为1。电阻与电容值根据下式求 When using a computer to process human physiological signals, the cut-off frequency of the low-pass filter needs to be divided into a plurality of steps from 5 Hz to 3 kHz. To this end, we designed a programmable active low-pass filter, are described below: Figure 1 is the program-controlled active low-pass filter schematic. In order to make the pass-band amplitude-frequency curve straight, we choose Berthold voltage-fed second-order filter. The active filter gain is selected as 1. Resistance and capacitance values ​​according to the following formula