Abstract 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.
A band pass active filter of the double tuned type, comprising: first and second negative impedance converter circuits; an R/C high pass filter connected to the input of said first negative impedance converter circuit; an R/C low pass filter connected to the output of said second negative impedance converter circuit; and a third R/C network, consisting only of series and shunt capacitance and resistance, connected between the output of said first negative impedance converter circuit and the input of said second negative impedance converter circuit, said network providing a low pass filter to the output of said first negative impedance converter circuit, a high pass filter network to the input of said second negative impedance converter circuit, and capacitive coupling between said negative impedance converter circuits.
Claim 2
Dependent Claim
126 words
A band pass active filter of the double tuned type, comprising: first and second negative impedance converter circuits; an R/C high pass filter connected to the input of said first negative impedance converter circuit; an R/C low pass filter connected to the output of said second negative impedance converter circuit; and a third R/C network, consisting only of series and shunt capacitance and resistance, connected between the output of said first negative impedance converter circuit and the input of said second negative impedance converter circuit, said network providing a low pass filter to the output of said first negative impedance converter circuit, a high pass filter network to the input of said second negative impedance converter circuit, and capacitive coupling between said negative impedance converter circuits.
Claim 3
Dependent Claim
22 words
The filter according to claim 1 wherein the shunt capacitance is at least two orders of magnitude greater than the series capacitance.
Claim 4
Dependent Claim
21 words
The filter according to claim 1 wherein the shunt capacitance is approximately one order of magnitude greater than the series capacitance.
Claim 5
Dependent Claim
55 words
The filter according to claim 3 wherein said third R/C network comprises a shunt resistor connected to the output of said first negative impedance converter circuit, a series resistor connected to the input of said second negative impedance converter circuit, and a pi-type capacitive coupling network connected between said shunt resistor and said series resistor.
Claim 6
Dependent Claim
72 words
The filter network according to claim 4 wherein the value of the shunt capacitors in said pi-type capacitive coupling network (Cp) is given by the following relationship: Cp Congruent Co -Cm Co/ Cm +Co where Co equals the capacitance of the capacitor in the input high pass filter network and the output low pass filter network, and Cm is the capacitance of the series, coupling capacitor in said pi-type capacitive coupling network.