Switch matrix

A switch matrix for selectively connecting at least one of N signal inputs to at least one of M signal outputs, N and M being integers greater than two, includes a cluster of N input switches arranged about each of the M signal outputs resulting in at least M clusters of N input switches, each input switch having a switch input and a switch output, the switch outputs being connected to respective signal outputs, the clusters and the input switches in the clusters being arranged to permit adjacent switch inputs of adjacent clusters to be connected to form input switch nodes; and a steering switch for each of the signal inputs. The steering switch selectably connects a signal input to an input switch node, wherein the combination of the steering switches and the input switches are operable to connect a desired signal input to a desired signal output.

BACKGROUND OF THE INVENTION

The present invention relates to electrical test instruments and, in particular, to a switch matrix for test connections.

Referring toFIG. 1, a typical cross-point switch matrix10is formed from rows and columns of output lines Oiand input lines Ii, respectively. “Switches”12are located at the cross points to allow connection of inputs to outputs. The switches may be, for example, simple mechanical switches, mechanical relays, or solid-state electronic equivalents thereto.

One limitation on the operation of the switch matrix10is that the upper frequency limit is affected by the “stub” lengths in the switch matrix10. A stub may be considered to be a conductor connected to a signal of interest, but not actually carrying the signal from input to output. For example, when the input INis connected to the output Oi, stubs include the conductor portion14and conductor portion16. In general, as the number of elements in the switch matrix10increases, the stub effects increase, limiting the frequency of the signal that may be switched.

SUMMARY OF THE INVENTION

A switch matrix for selectively connecting at least one of N signal inputs to at least one of M signal outputs, N and M being integers greater than two, includes a cluster of N input switches arranged about each of the M signal outputs resulting in at least M clusters of N input switches, each input switch having a switch input and a switch output, the switch outputs being connected to respective signal outputs, the clusters and the input switches in the clusters being arranged to permit adjacent switch inputs of adjacent clusters to be connected to form input switch nodes; and a steering switch for each of the signal inputs. The steering switch selectably connects a signal input to an input switch node, wherein the combination of the steering switches and the input switches are operable to connect a desired signal input to a desired signal output.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 2, a switch matrix20(4×9) is configured to minimize output line stubs. The four input switches associated with each output O1, O2, O3, O4, O5, O6, O7, O8, and O9are clustered about the respective outputs. The stubs associated with the outputs are then little more than the connected switch leads. However, the stubs of the input lines are still substantial (in fact, probably greater than theFIG. 1example). For example, when the input Iiis connected to the output O1, the input stubs are the conductor portion22and the conductor portion24.

Referring toFIG. 3, a switch matrix30(4×9) is configured similar toFIG. 2with respect to the output clusters, but also now includes sixteen input nodes Iix, each having stub-lengths similar to the output stubs (little more than the connected switch leads). To provide for connection of the inputs to the input nodes, an additional layer of switching is added. For example, referring toFIG. 4, each input Iiis provided with a cluster of steering switches to connect the input Iito the nodes Iix(in this case, four nodes available for each input). There are unshown conductors between the steering clusters and the input nodes to carry the respective signals, but these will not contribute to the stub-lengths. The steering clusters may be considered to be input node multiplexors and, in fact, be implemented that way also.

Referring toFIG. 6, a switch matrix50(3×19) has nineteen output clusters (1to19) and sixteen input nodes (A1to A5, B1to B5and C1to C6). The larger the maximum number of outputs sharing an input node, the smaller the input multiplexors can be.

The clusters and the input switches on the clusters are arranged so that adjacent switch inputs of adjacent clusters are connected to form input switch nodes. The steering switch selectably connects a signal input to an input switch node. The combination of the steering switches and the input switches operate to connect a desired signal input to a desired signal output.

How small the cluster sizes can be are basically limited by the size of the switches in the cluster. To further increase the density, the clusters may be provided on both sides of a printed circuit board, thereby doubling the number of possible inputs.

The minimizing of the stub lengths allow the switching of higher frequency signals, e.g., 1 GHz. In addition to providing higher frequency capability, the clustering of switches may also improve DC performance by minimizing the physical locations that may need to be guarded (i.e., providing adjacent conductors driven to a virtually matching voltage to minimize leakage effects).

The switches in the above-described switch matrixes may be, for example, simple mechanical switches, mechanical relays, or solid-state electronic equivalents thereto.

The designations of input and output are largely for ease in understanding of this disclosure. In general, the designations may be reversed without significance.

While the examples above show a single switched conductor, the devices may include multiple parallel conductor switching. For example, with RF inputs and outputs it may be desirable to for each switch to switch both a signal and a ground conductor.