Pole Switched Matrices
Crosspoint and Tree Matrices are discussed here Crosspoint and Tree Matrices. Crosspoint matrices are created from arrays of SPST relays arranged as a simple grid, Tree Matrices are created from Tree Multiplexers to provide solutions for matrices requiring high RF bandwidths. In creating these matrices they also restrict the connectivity that can be provided. There are also matrices which are simple crosspoint matrices but the crosspoint array is subdivided by isolation relays that provide matrices with intermediate bandwidths.Yet another type of matrix used by Pickering Interfaces whose purpose is not to increase bandwidth but to improve density and lower the relay count. The approach is most suited to matrices that use EMR's. They are referred to as Pole Switched Matrices but also referred to as Efficient Matrices.
Pole Switched Matrix
Many EMR's that are commercially available are offered as DPDT (Double Pole Double Throw) relays, each package has two mechanically linked (dotted line) changeover relays.
DPDT Relay
The arrangement imposes some connection limitations on the use of the matrix. An X connection can only be connected to either an odd or even Y without creating routing management issues.If for example X2 connects to Y1 the changeover prevents it also connecting to Y2 - a limitation that does not exist when SPST relays are used.
However, where a crosspoint switch on a Y=6 matrix would use 6 off relays to implement each X connection the Pole Switched arrangement uses just 4 relays (one changeover and three crosspoint relays), a significant saving. In a switching system that means a matrix with more X connections can be created for the same PCB footprint.
Example: For a Y=6 matrix and a system which has room for 256 relays a matrix could be 42x6 while the Pole Switched matrix could be 64x6. That could make it possible to implement a matrix in a single slot of PXI rather than two slots.
Connection Limitations
In order to simplify the use of Pole Switched Matrices the Pickering interfaces driver prevents connections which link two Y connections together on the same X connection. Although this limitation could be more flexible (for example in the drawing above X1 could link to Y1 and Y3) it is simpler to limit the functionality.In the majority of cases users do not connect directly to the Y axis of large matrices, instead the X axis is used for both the system instrumentation and the unit under test connections so that the matrix size is defined only by the number of concurrent paths required for each test.
Using X axis connections to limit Y axis size to the number of concurrent connections required
Some users however may want to access the Y connections. Using the 256 relay Y=6 example the recommended method is to use X1 to X6 to provide the Y access and then to use the remaining 58 X connections (of 64) as the X axis connections. Using this method imposes no restrictions on the connectivity that can be achieved, and the matrix size is still significantly larger than can be achieved with a simple crosspoint matrix. PCB tracking tends to be a little more complex, and this may force an increase in PCB layer count in some cases.
Data Sheet Depiction
Data sheets for Pole Switched Matrices include a schematic similar the image below (adapted to the matrix size) to show the allowed paths.
The only path type not allowed is as shown in red where two Y connections are linked on the same X, a use case which has no common application. If a user adopts using X axis connections to provide access to Y then this limitation also does not exist as if X1 to X6 become Y1 to Y6 by closing X1Y1, X2Y2, X3Y3, X4Y4, X5Y5, X6Y6 then links between any Y connections are then allowed.
