| 摘要 |
PURPOSE:To establish BPF having the fourth cut-off characteristics substantially with high selectivity, by connecting the first capacitor to the input terminal, grounding the one end, and connecting the second capacitor and taking another end as new input terminal. CONSTITUTION:In RC active filter suitable to obtain the tuning characteristics higher in the selectivity, the capacitor 17 is connected to the input terminal 13 and one end is grounded, the capacitor 16 is connected and another end is taken as the new input terminal 15. The T-type circuit network consisting of CR circuit is formed between the terminal 15 and the input summing point 18 of the operational amplifier 1, and the summing point 18 is taken as a virtual ground with parallel feedback effect. Further, the capacitance is taken as C16>C17, and the transmission frequency characteristics from the terminal 15 to the terminal 13 show the band- pass characteristics having the low cut-off frequency fL and the high cut-off frequency fH. Thus, BPF having substantially the fourth order cut-off characteristics and higher selectivity can be obtained by adding further two capacitors to the active filter. |
