Abstract: A RC coupling filter, especially an input filter for receivers of centralized ripple control systems, with at least two similar active RC four terminal networks with at least one amplifier each, each four terminal network having an input and every two adjacent RC four terminal networks being interconnected by means of exactly one coupling admittance connected between the inputs of the adjacent RC four terminal network, wherein, if the signal to be filtered is introduced into the input of the first RC four terminal network, a feeding admittance is connected at one end to the input of the first RC four terminal network, the signal to be filtered being introduced into the other end of the feeding admittance.

Abstract: A coupling filter is formed from a plurality of four terminal networks. Each active four terminal network preferably has a bypass admittance, two filter admittances, a feedback admittance, and an amplifier. One end of the bypass admittance and of the filter admittances are connected to each other and to the input of the four terminal network, and one end of the feedback admittance is connected to the other end of the first filter admittance and to the input of the amplifier. The remaining ends of the second filter admittance and of the feedback admittance, as well as the output of the amplifier, are connected to each other and to the output of the four terminal network. Thus, except for the first four terminal network and the last four terminal network, the input of each four terminal network is connected by way of a coupling admittance to the output of the preceding four terminal network and said input is connected by way of a second coupling admittance to the output of the following four terminal network.

Abstract: An active band-pass filter comprises at least one unit consisting of two filter sections connected in tandem via capacitive coupling impedances, each section including an operational amplifier with an R/C network in its feedback path. The network has two parallel branches, one of them being divided into two series capacitances whose junction is grounded through a shunt resistance and is also connected to the output of the other section through one of the coupling capacitances acting as a feedback impedance. One of these series capacitances, lying between that junction and the inverting input of the operational amplifier, is also in series with an input impedance which in the case of the first section is a high-ohmic resistor and in the case of the second section is the other coupling capacitance. In a modified unit, constituting the dual of the first one, all the capacitances of the former are replaced by resistances and vice versa.