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added spring 2009
***UPDATED to include new backplane components
***UPDATED to include new backplane components
***An older version of this library was used for the digital board
***An older version of this library was used for the digital board
==Summary of Spring 2009 Work==
At the end of the fall semester, Dr. Jones, Igor, and I determined that the amplifier/summing circuit we had designed simply didn’t have sufficient performance characteristics to be useful for GlueX. During the beginning of the spring semester, Igor came up with a new design, utilizing more transistors, to provide the high gain, fain response, picoseconds resolution amplifier that we needed. The design performed flawlessly both in MatLab simulations and in a handmade single channel prototype. The first of my goals for the spring 2009 semester was to capture the schematic for this new amplifier into Altium designer, and layout a new amplifier board. The second of my goals, of course, was to complete production of the digital control board prototypes.
Since the fall semester left us with three unpopulated digital control board PCBs, getting those PCBs assembled with their components was the first priority. I began the semester by tracking down all of the components we needed (some of which were selected at the end of the fall semester), and making appropriate substitutions for components whose availability had changed since the fall. In the process of selecting these components, I noticed several places where it seemed like power consumption on the board may be somewhat high. To fix this, I developed a spreadsheet in Microsoft Excel that calculates optimal resistor values to use for to obtain a specified voltage divider stiffness. With this tool, I was able to optimize power consumption across the board, and select appropriate components. Once all components had been selected, ordered, and received, we sent the order out to Screamin’ Circuits for assembly. The boards came back several weeks later, and are currently awaiting testing by some undergraduates who will be in the lab this summer.
While Igor was finalizing his amplifier/summing circuit, I worked briefly on design of the backplane. A number of details regarding trace impedance and board dimensions were ironed out. Nonetheless, many problems still remain which I will need to tackle over the summer. The first of these problems is that we have yet to find an appropriate low cost coaxial connector to route signals off the backplane. In addition, screws with which to mount the backplane to the tagger must be selected so that appropriate holes can be created for them on the PCB.
Once we were satisfied that the amplifier/summing circuit performed as required, I shifted work from the backplane to the amplifier board. Around the same time, I began working on a poster to present my work at the Frontiers in Undergraduate Research Exhibition held during Open House Weekend here at UConn. If you’re interested in my poster, check it out here.14:49, 5 May 2009 (EDT)14:49, 5 May 2009 (EDT)[[User:Underwood|Underwood]]
To start the amplifier/summing circuit project, I searched high and low for information about how to handle multi-channel designs in Altium. Not surprisingly, the first Google result on the query “multichannel design Altium” had everything I was missing during the fall when I was trying to lay out the original amplifier circuit. Using my new knowledge of Altium’s multichannel capabilities, I captured Igor’s new design into the schematics editor of Altium Designer. With proper nested schematic sheets, the entire 30 channel amplifier/6 channel summer design was compressed into just 4 schematic sheets, vs. the ~40 or so that would have been required had I laid out the complete schematics of the old design.
I spent about a week and a half trying to figure out how to handle nesting independent nets from a repeated subsheet into another repeated subsheet which also produces independent nets from the nets of the first sheet. This sounds somewhat complicated, and I suppose perhaps it is a somewhat unique situation, since none of the ~5 sample multichannel projects included with Altium had such a construction in them. Basically, each summing circuit has five amplifier subcircuits, each of which puts out its own signal independent of the other four. From the perspective of the entire board, there are 6 summers, each of which has five independent signals coming from the amplifiers, and one summed signal. Determining how to get Altium to realize the proper connections from each individual amplifier, through that amplifier’s summer, to the main schematic was a complicated mess of naming conventions, but eventually I was able to make Altium reflect all of the appropriate connections in the PCB view. Though there are a few net naming issues still to be resolved, this problem has mostly been ironed out.
The final few weeks of the semester were spent laying out components in the PCB view of Altium. As of right now, a compact design for an amplifier measuring 0.183”x~1.3” has been completed. Making use of 0201 size components, this amplifier is approximately .2” shorter than the old design, despite incorporating an extra transistor. The amplifier design features an isolating ground trace running the length of the amplifier to prevent crosstalk between channels. A prototype layout of the summing circuit has also been completed, though some layout issues there remain to be resolved over the summer.