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.
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.
To implement a crosspoint switch only a single SPST relay is required, but making use of the second DPDT relay can mean that
a single relay package can serve two crosspoint connections. To achieve this each X connection has a changeover relay (SPDT)inserted
which connects to one of two tracks, one goes to cross points on even Y bus connections (Y2, Y4 ..) and the other goes to
odd Y bus connections (Y1, Y3 ...).
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.
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 requiredFor these users the Pole Switched Matrix imposes no restrictions on connectivity as shorts (equivalent to Y to Y when the instruments are on Y) across the instrumentation connections can be applied.
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.
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.