Instrument Backplane 3-MDM Rev B to Rev C changes

Configurable jumpers instead of traces to connect Chassis-GND to AGND

ELE-C587-101 Rev B boards have a PCB error where the chassis and AGND connections have not been connected. The schematic is correct. The Altium work around is to drop a via on either plane and run a trace from the pad the the via. In this way the connection is made to the polygon. The original error occured due to the way Altium creates it's thermal attachments to polygons.

configurable jumpers for Detector Bias lines

Add a series of jumpers to provide the option of routing detector bias lines from BC3 DACs (DAC00 to DAC15) OR the upper half of BC2 DACS (DAC16 to DAC31). This means 3-way jumpers and we should populate those that route BC2 DACs and list the other jumper as DNP.

Changed R106 to R121 inclusive from 2k to 15kOhm (SQ1FB resistors)

On Thu, 9 Dec 2010 15:49:34 -0800: "Future focal planes will use MUX09a, for which we have been using 15 kOhm (~1.75 phi0 over the ADC range). We believe that this choice is adequate. If you want to be conservative (since resistors are cheap), you could also order ~12.3 kOhm resistors (which would give ~2.1 phi0, closer to BICEP2's deployment value) just in case. The plan for now is 15 kOhm. We will also need to support a couple of existing legacy focal planes for testing purposes, which for the time being will still have some MUX07a's. For this purpose we'll need a couple of custom backplanes with ~6-8k resistors. I think that we are OK on this front (with our existing test crates), but if it comes down to it we may request an unfilled or custom backplane in the future. I think that we can cross that bridge when we come to it."