Single-transistor all-pass networks

A network configuration consisting of a resistive twoport bridged by a lossless one-port is considered. It is shown that in certain cases this configuration is capable of realizing a voltage transfer function equal to that of a constant-resistance passive lattice. As a special case, conditions are derived on the two-port parameters for the structure to be all pass. It is determined that a single transistor suffices to realize the two-port network, thus resulting in a very simple all-pass structure; only one coil, one capacitor, and one transistor are necessary to realize a second-degree all-pass voltage transfer function. Higher order transfer functions can be realized by adding an branch per each additional second-order factor to the same transistor circuit. In the second-order case, losses in the coil can be compensated. In higher order realizations coil losses cannot be compensated, but a design technique which achieves an arbitrarily close approximation to the desired all-pass transfer-function is presented. Methods of cascading lower order sections are discussed and experimental results are given.