Transistor circuit constructions for active type band pass filters

Claim 1

AN ADJUSTABLE FREQUENCY SELECTIVE CIRCUIT FOR TRANSMISSION OF SIGNALS OF A PASS BAND CENTER FREQUENCY WHICH MAY BE SELECTIVELY VARIED OVER A PREDETERMINED RANGE OF FREQUENCIES, AND FOR ATTENUATION OF SIGNALS ABOVE AND BELOW SAID CENTER FREQUENCY WITH AN ATTENUATION GRADIENT BETWEEN THE CENTER FREQUENCY AND THE ATTENUATED FREQUENCIES, SAID ATTENUATION GRADIENT BEING OF A SELECTIVELY VARIABLE DEGREE OF STEEPNESS, SAID CIRCUIT COMPRISING: (A) FIRST AND SECOND RESISTANCE AND CAPACITANCE FREQUENCY SELECTIVE AMPLITUDE TRANSFER NETWORKS TANDEM CONNECTED THROUGH A BUFFER MEANS, SAID TRANSFER NETWORKS EACH COMPRISING AN IMPEDANCE MEANS SERIALLY CONNECTED IN THE IMPEDANCE PATH AND AN IMPEDANCE MEANS SHUNT CONNECTED ACROSS THE SIGNAL PATH, THE SERIALLY AND SHUNT CONNECTED MEANS OF ONE OF SAID TRANSFER NETWORKS COMPRISING A RESISTOR AND A CAPACITOR, RESPECTIVELY, AND THE SERIALLY AND SHUNT CONNECTED MEANS FOR THE OTHER TRANSFER NBETWORK COMPRISING A CAPACITOR AND A RESISTOR, RESPECTIVELY, (B) MEANS FOR SIMULTANEOUSLY VARYING THE MAGNITUDE OF THE SERIALLY CONNECTED IMPEDANCE MEANS OF ONE OF THE TRANSFER NETWORKS AND VARYING THE MAGNITUDE OF THE SHUNT CONNECTED IMPEDANCE MEANS OF THE OTHER TRANSFER NETWORK TO SELECTIVELY VARY THE PASS BAND CENTER FREQUENCY BETWEEN VARIOUS VALUES IN SAID PREDETERMINED RANGE OF FREQUENCIES AND INDEPENDENTLY OF VARIATIONS IN STEEPNESS OF ATTENUATION GRADIENT, (C) POSITIVE FEEDBACK MEANS BRIDGES ACROSS THE TANDEM CONNECTED TRANSFER NETWORKS, AND (D) SAID POSITIVE FEEDBACK MEANS INCLUDING ADJUSTABLE MEANS FOR VARYING THE FEEDBACK LOOP GAIN TO SELECTIVELY VARY THE DEGREE OF STEEPNESS OF THE ATTENUATION GRADIENT AND INDEPENDENTLY OF VARIATION IN CENTER FREQUENCY.