ACTIVE CIRCUITS SIMULATING INDUCTANCES

摘要

1532982 Active impedance converters POST OFFICE 4 March 1976 [20 March 1975] 11582/75 Heading H3U An active impedance element is constituted by three impedances C16, R27, R28 in series and an amplifier A6, the non-inverting input of the amplifier being connected to the junction between the first and second impedance, and the inverting input and the output being connected via a fourth impedance C 18 to the junction between the second and third impedance. As shown, with the first and fourth impedances capacitive, and the second and third impedances resistive, the impedance between the ends of the series chain of the three impedances is R27 + R28 + jw R27.R28.C18. The element is connected as the shunt arm of a T network 26 having C15, C17 as its series arms to give a high pass response. If first and fourth impedances are made resistive and the second and third capacitive, as in the circuit 27, then the impedance between the ends of the series chain R22, C12, C13 is given by 1/jw C12 + 1/jw C13 - 1/w2 C12.C13.R24. This element forms the shunt arm of a further T network having R21, R23 as its series arms, and forming a lowpass filter. The two filters have their inputs and outputs connected in parallel to provide a band stop response. A similar high pass section alone is described with reference to Fig. 6 (not shown). In another high pass filter the shunt element of the filter includes a gyrator circuit 24. The filters are described as forming part of a multi-frequency signalling system.