Expected SHARC2 detector noise

For a 30% quantum efficiency and a 5" square pixel, the expected noise from the sky at 350 um is NEP(electrical) = 3.6 x 10^-16 W/sqrt(Hz). A good detector with 10 Mohm impedance has a responsivity of about 1.2 x 10^8 V/W, so the sky noise would be 43 nV/sqrt(Hz). For the JFETs to make no more than a 5% contribution to the total noise, the JFET noise should be <= 14 nV/sqrt(Hz).

The responsivity scales approximately as sqrt(impedance). For detectors biased with an AC waveform, the target range of impedance is 5-10 Mohm, so the JFET noise would preferrably be <= 10 nV/sqrt(Hz) at ~30 Hz in case the low end of impedance results.

For detectors biased with a DC waveform, the target range of impedance is 10-40 Mohm, so the JFET noise would preferrably be <= 14 nV/sqrt(Hz) at ~3 Hz.

Last modified Monday, 17-May-1999 06:32 PDT
cdd@socrates.caltech.edu