FREQUENCY SYMMETRICAL IMPEDANCE INVERTER
Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2001-Oct-10
An impedance inverting circuit is commonly used to couple the output of an active stage to the-input of a crystal filter in order to obviate a reduction in the output intercept point of the active stage from the high, off frequency impedance of the crystal filter. Cost effective monolithic crystals usually have the electrode frequencies below the design center frequency of the required filter. The input impedance characteristic of the resulting inverterlcrystal filter structure is such that the peaks of the "flybacks" are assymmetrically placed about the design center frequency. An inverter circuit is described in which substantially geometric symmetry may be obtained in the flybacks.