The Forward-Viewing Analog Module (FAM) helps to convert
signals from Bands 31-36 into signals within the range of
the A/D converter. These bands are used to create Surface/Cloud
Temperature and Cloud Top Attitude, and operate in the 10.78
- 14.385 µm region.
Bands 31-36 are detected by photoconductive HgCdTe detectors
(which are not integrated-circuit compatible) and appear at
the Focal Plane Assembly interface as 60 individual signals.
The electronics challenge of these bands consists in detecting
with 12-bit accuracy full-scale signals as low as 800µV
(in the presence of background offsets of up to 650 mV) as
well as protecting these low-level signals from noise pickup
across the interface between the 83K focal plane and the electronics
(which operate at ambient temperature).
The CLAM, located immediately adjacent to the cooler, contains
60 hybridized preamplifier circuits, each of which provides
an offset capable of covering the entire range in 64 steps.
Further amplification and A/D conversion occur in the Forward-Viewing
Analog Module, which is equipped with an 8-bit fine offset
correction. These correction loops are nested, which provides
a combined offset correction precision of 14 bits. The offsets
are automatically adjusted as needed to keep the entire signal
within the range of the A/D converter.