Changes

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.

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.

[[Image:Digital Board, Populated.JPG|thumb|The populated digital board, with a tube of Chap-Block^TM for size comparison.]] 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.

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.