Specifications

Version 1.1 rev Jan 2013
Page 39
iXon Ultra
, Features and Functionality
3.1.2 - EM Gain & Read Noise
As explained in Section 3.1.1, EMCCD sensors allow the detected signal to be amplied on the actual sensor itself
before being readout through the output amplier and digitized by the Analog to Digital (A/D) converter. The reason
that this on-chip-multiplication process gives such a signicant improvement in low-light detection is that it negates the
effect of any electronic noise that may be generated by the read out electronics.
All CCD cameras have an associated minimum electronic noise oor, which is often termed the Read Noise of the
system. Read noise is produced during the readout process mostly by the output amplier, but also has contributions
from the digitization electronics. This sets the minimum signal level that can be detected by the camera, as any signal
level below the read noise level will be indistinguishable from the read noise itself.
Read noise has therefore been the major limiting factor for low-light level detection in CCDs for many years until
the introduction of EMCCD cameras by Andor Technology in 2000. By applying EM Gain, a weak signal that would
otherwise be indistinguishable from the read noise can be amplied above the read noise level and thus be read out as a
useful signal. This amplication of the signal before being read out effectively reduces the read noise level of the camera,
and even at relatively modest EM Gain settings the effective read noise can be reduced to less than 1 electron r.m.s.
NOTE: Read noise increases with increased readout rate, therefore the application of EM Gain provides an
advantage at higher readout rates, as any increase in the read noise can be overcome simply by increasing
the EM Gain. For example, an iXon Ultra 897 typically has a read noise of 50 electrons rms when reading out at
10MHz. This can easily be reduced to < 1 electron by applying > x50 EM Gain.