| 摘要 |
A double tuned active band pass filter is formed by utilizing a pair of band pass filters including negative impedance converter (NIC) circuits coupled with a pi-type or T-type capacitive coupling network, the capacitances of which provide the output capacitance of the first stage in the input capacitance of the second stage and a coupling capacitor. The first stage and the coupling capacitor form essentially a current generator allowing current mode operation of the second stage. In one mode, the coupling capacitor is chosen to be roughly two orders of magnitude less than the capacitors in the leg of the pi, the capacitances of which are the natural capacitances of the individual filter stage. In another mode, the coupling capacitor is made to be somewhere on the order of magnitude of the capacitance of the original devices, and the legs of the pi are adjusted to be equal to the value of the coupling capacitor divided by one plus the decimal fraction that the coupling capacitance bears to the basic capacitance. In a T-type configuration, greater, rather than lesser capacitance is used.
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