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 (Double Pole Double Throw) Relay
DPDT Relay

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 ...).
Pole switch matrix

The crosspoint switches on Y1 and Y2 are two pole relays contained in the same package (for an EMR a DPDT relay is used), a pattern repeated throughout the design. Connections are made from X through the SPDT relay and then by closing the crosspoint relay. The SPDT prevents either the odd or the even Y axis connecting to the X connection according to its position.

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. 

Matrix useUsing X axis connections to limit Y axis size to the number of concurrent connections required 

For 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.

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. 
pole switched matrices scehmatic 

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. 

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