Variable electronic allpass delay networks

The m.o.s.t. analogue switch has provided the opportunity for a fresh study of allpass delay networks using the sample-and-store principle. This letter describes networks designed to produce a delay which can be controlled precisely by an externally applied sampling signal. They are suitable for realisation as integrated circuits, one example comprising a 1 in-square thin-film circuit with one m.o.s.t. integrated circuit and one bipolar circuit attached. This type of circuit is seen as the replacement for the bulky and expensive fixed-delay networks used at present for the transversal filter, the basic element of automatic and adaptive equalising systems for high-speed data transmission, with the added versatility of variable delay.