  The Gemini Planet Imager (GPI) is a new facility, extreme adaptive optics
(AO), coronagraphic instrument, currently being integrated onto the 8-meter
Gemini South telescope, with the ultimate goal of directly imaging extrasolar
planets. To achieve the contrast required for the desired science, it is
necessary to quantify and mitigate wavefront error (WFE). A large source of
potential static WFE arises from the primary AO wavefront sensor (WFS)
detector's use of multiple readout segments with independent signal chains
including on-chip preamplifiers and external amplifiers. Temperature changes
within GPI's electronics cause drifts in readout segments' bias levels,
inducing an RMS WFE of 1.1 nm and 41.9 nm over 4.44 degrees Celsius, for
magnitude 4 and 11 stars, respectively. With a goal of $<$2 nm of static WFE,
these are significant enough to require remedial action. Simulations imply a
requirement to take fresh WFS darks every 2 degrees Celsius of temperature
change, for a magnitude 6 star; similarly, for a magnitude 7 star, every 1
degree Celsius of temperature change. For sufficiently dim stars, bias drifts
exceed the signal, causing a large initial WFE, and the former periodic
requirement practically becomes an instantaneous/continuous one, making the
goal of $<$2 nm of static WFE very difficult for stars of magnitude 9 or
fainter. In extreme cases, this can cause the AO loops to destabilize due to
perceived nonphysical wavefronts, as some of the WFS's Shack-Hartmann quadcells
are split between multiple readout segments. Presented here is GPI's AO WFS
geometry, along with detailed steps in the simulation used to quantify bias
drift related WFE, followed by laboratory and on sky results, and concluded
with possible methods of remediation.
