16:4 Channel/Coupling Selector for CCD and CMOS Imager Testing
Pulse Instruments is a sister company to PRL. PI makes the world's finest automated test stations for Infrared Focal Plane Arrays, CCDs, and CMOS Imagers.
A customer wanted to test devices with up to 16 outputs, but the did not have sufficient budget to purchase a test system with 16 simultaneous ADC channels. They chose to multiplex 16 video inputs into a modest system with 4 ADC channels, and they also wanted the option to select AC or DC coupling, all under computer control.
We built this test mux using all off-the-shelf products from PRL, requiring no electrical engineering. A small amount of mechanical design work was done to enclose the solution.
The Task:
Multiplex 16 channels each of high-speed, low-noise video signals into 4 preamplifier/ADC channels, with a choice of AC or DC coupling for each path.
The Solution:
A set of four PRL-854-RM-SMA switches and four PRL-852A-RM-SMA switches were integrated into a PRL-985 series extrusion.
The switches are controlled by a PRL-USB-I/O module and all the switches are powered by the bundled PRL-760C AC/DC adapter, and distributed by a PRL-730 DC Power Distribution module.
Control lines to each PRL-854-RM switch select one of 4 video signal to feed into the measurement path. Each of the 4 measurement paths travels through a pair of 1:2/2:1 switches, with one path containing a PRL-SC-104A, 0.1 µF DC block for AC coupling. The remaining path is wired through for DC coupling. The final outputs are cabled to a set of SMA bulkhead adapters on the output endplate.
The solution could have been implemented as a set of separate modules on the bench or on a Velcro plate:
but we wanted to make the solution rugged and portable, so we chose to integrate everything into a PRL-985 series enclosure.
The PCBs for nearly all 3-digit PRL part numbers will mount vertically in the slots of the PRL-985 extrusion:
and we secured the PRL-854-RM modules to the endplates via the SMA nuts. A mounting plate was drilled to support the PRL-852A modules in the interior of the assembly, and the remaining modules were screwed directly to the custom endplates fabricated by Cam-Expert (though we have also used Front Panel Express with excellent results, using the same design files).
The top decal was printed on a Zebra Z6M thermal label printer.
The resulting product, the PRL-4528, is now available for purchase as a standard product.
Future Features
Due to the inherent modularity of the solution, the test muxes can be easily modified or expanded to handle an arbitrary number of input channels by adding additional cascade stages.