IRAC Instrument Handbook - IRSA - California Institute of Technology

Instrument Description 13 Electronics
IRAC Instrument Handbook
Figure 2.6 : Non-linearity curves for the IRAC detectors. The detector responses are fairly linear
until saturation, where there is a steep drop-off in responsivity.
2.4 Electronics
2.4.1 Hardware
IRAC has no moving parts (other than the shutter, which was not operated in flight). The instrument takes
data by staring at the sky and sampling the arrays between resets. IRAC was capable of operating each of
its four arrays independently and/or simultaneously. All four arrays were used during normal, full-array
operation.
2.4.2 Fowler Sampling
Multiple (Fowler) sampling is used to reduce the effective read noise. This mode of sampling consists of
taking N non-destructive reads immediately after the reset, and another N non-destructive reads near the
end of the integration. Differencing is performed in the IRAC electronics to generate one integer value
per pixel per exposure to store on the spacecraft and transmit to the ground. The Fowler N used for an