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Abstract

A fully monolithic cross-point switch matrix overcomes the isolation problems between unconnected ports of the prior art. An Isolation Enhancement Network (IEN) is connected between each of the input and output transmission lines at each of the cross-points. The switch matrix is comprised of a tiled interconnection of M.times.N of the 1.times.1 switch/IEN (SIEN) cells, where N and M are the number of input and output ports respectively. Each of the SIEN cells can be independently configured into one of two operating modes, connected or unconnected. The switching element is configured to provide a high isolation path between the input and output lines in the unconnected mode of operation. In this case, a small fraction of the input signal injected at the input port appears at the output port. This output signal is comprised of two components. The first component arises from a number of stray coupling mechanisms between the input and output lines but does not include the portion of the input signal which passes through the IEN. The dominant area of this stray coupling occurs at the point where the input and output transmission lines cross. The second component of the output signal is purposely injected via the IEN. The IEN couples a small portion of the input signal, adjust its amplitude and phase, and then recouples it to the output line so that the resultant signal has the same amplitude but is 180 degrees out-of-phase with the first component. The two components cancel each other yielding an improvement in the isolation between the two ports. The compensation signal injected by the IEN into the output line is significantly lower than the main signal component when the switching element is in the connected state, thereby allowing the input signal to be routed to the output with insignificant perturbation.

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