The Si Analog Signal Processing electronics provide four Si clocks. Observation modes for the IRS require clocking the Si detectors using the Timing Pattern Generator (TPG) with specific timing patterns as defined below.
2.9.3.1 Basic Definitions
In order to discuss the IRS array clocking and data collection it is necessary to define several terms in addition to those defined in Section 1.2:
Sample:A 16-bit integer resulting from a single A/D conversion of a pixel signal.
Frame: A single clocking through a detector array, visiting every pixel. There are four frame types used in observations:
· Sample Frame: A frame in which each pixel is sampled (read).
· Reset Frame: A frame in which each pixel is reset.
· Boost Frame: A frame in which each pixel is reset with a boost voltage applied.
· Spin Frame: A frame in which each pixel is just addressed. No read or reset is applied. Spin frames allowed continuous clocking patterns without affecting the charge of a pixel.
Frame Count: The number of sample frames.
Two data collection techniques were used in general science data collection:
Spinning Double Correlated Sampling (DCS): Scheme in which the first frame after a reset frame and the frame just before the next reset were sampled, with spins in between. Peak-Up Acquisition (PUA) employed DCS mode.
IRS Raw or Sample-Up-the-Ramp (SUR): Scheme in which sample and spin frames were obtained between a reset frame and the next reset/boost frame; i.e., the ramp is sampled. Science data were collected in SUR mode.
In addition, we define different time amounts:
Frame Time: Time required to clock through one Si frame. IRS frame times are in standard seconds (derived from a 40 MHz oscillator on the CE I/O board).
Exposure Time: The time for which the Timing Pattern Generator was running during an IRS exposure (“wall clock time”).
Effective Data Collection Event (DCE) Time, or Effective Exposure Time: The time for which the Timing Pattern Generator was actively collecting valid data, or the time between detector resets (“integration time”).
DCE Time or Execution Time: The time between and including detector resets (= effective DCE time + reset time).
