High Performance in Low Light
Recently, CCD manufacturers have introduced novel, high-sensitivity CCDs engineered to address the challenges of
ultra-low-light imaging applications – without the use of external image intensifiers. The new detectors utilize revolutionary on-chip multiplication gain technology to multiply photon-generated charge
above the read noise, even at supravideo frame rates.
This special, signal-boosting process occurs before the charge reaches the on-chip readout amplifier, effectively reducing the CCD read noise by the
on-chip multiplication gain factor, which can be greater than 1000x. The main benefit of the technology, therefore, is a far better signal-to-noise ratio for signal levels below the CCD read-noise
The principal difference between a charge-multiplying CCD and a traditional CCD is the presence of a special extended serial register, known as a multiplication register, in the new device (see
Figure 2). Note that since the on-chip multiplication gain takes please after photons have been detected in the device’s active area, it is possible to adapt the new technology to all current CCD formats
and architectures. Recently, for example, cameras utilizing back-illuminated versions of these new charge-multiplying CCDs have been introduced (e.g., the Photometrics Cascade:512B).
accelerated from pixel to pixel in the multiplication register by applying higher-tha-typical CCD clock voltages (up to 50 V). Secondary electrons are generated via an impact-ionization process that is initiated
and sustained when these voltages are applied. The on-chip multiplication gain can be controlled by increasing or decreasing the clock voltages; the result gain is exponentially proportional to the voltage.