Both the response and the noise of the detectors have been characterized as function of signal strength. Tab. 5.1 summarizes the overall properties of the detectors.
For sensitivity calculations, the noise per reset interval may be summarized as
with S the signal in V/s and
dimensionless (happens to be equal to
the reset time in seconds).
The empirically determined noise parameters
(read noise, in
V/s)
(dark current noise, in
V/s), and
(signal shot noise,
V
/s
)
have been obtained by
forcing a fit through this function, and are summarized in
Tab. 5.2.
For the SW grating and the FP detectors the function works well up to a
sec.
For the LW grating detectors the function does not work well in
describing the
dependency, and the resulting values are not
necessarily directly to be associated with read noise and dark noise.
Parameter values are chosen in such a way that they give the best
description for the short reset intervals.
For Band 4, test measurements show consistently a very poor increase
of SNR for sec.
The parameters listed apply to
= 1 sec and
= 2 sec. For
longer
no improvement in noise should be expected, but the
function still applies.
detector | T | bias | minimum | int. ![]() | average response | min. system | |
system noise ![]() | ![]() ![]() | ||||||
(K) | (V) | ( ![]() | (electrons) | ( ![]() |
( ![]() | (W/ ![]() | |
gain=16 |
![]() | ||||||
Gr-InSb | 3 | - | 0.7 | 35 | 0.32 | 3.0 | ![]() |
Gr-Si:Ga | 3 | 12 | 1.5 | 75 | 0.32 | 1.6 | ![]() |
Gr-Si:As | 4.5 | 3.0 | 3.0 | 150 | 0.40 ![]() | 1.5 | ![]() |
Gr-Ge:Be | 2 | 0.6 | 2.0 | 100 | 1.00 | 1.3 | ![]() |
F-P-Si:Sb | 10 | 1.1 | 1.1 ![]() | 70 | 0.40 | 0.007 | ![]() |
F-P-Ge:Be | 2 | 0.6 | 3.0 | 200 | 0.40 | 0.0037 | ![]() |
Notes to Tab. 5.1:
All minimum noise and NEP's are conservative values for sec
and gain=16 .
's include the transmissions of the instrument
(i.e., directly relate to
's).
1) values listed for element 2; noise = 0.7 V/s for element 1
2) excess photon noise at V/s
3) measured at a signal power at which photon noise is negligible;
except FP-Ge:Be where still some photon-noise is suspected; estimated
photon-noise free =
W/
4) int. is intercept: photon noise at signal = 10 V/s
5) 1 Jy = WHz
, ISO telescope area taken as
0.28 m
Band | 1 | 2 | 3 | 4 |
detector | InSb | Si:Ga | Si:As | Ge:Be |
range ( ![]() | 2.38-4.05 | 4.05-12.0 | 12.0-29.5 | 29.5-45.2 |
![]() | 0.75 | 0.75 | 1.00 | 1.56 |
![]() | 0.70 | 1.50 | 3.00 | 2.00 |
![]() | 0.10 | 0.13 | 0.14 | 0.32 |