Channel matching error or channel mismatch is defined as the difference between the CCD sensor outputs at a certain video level. We work to ensure our channel matching error is as small as possible and that the channel matching is automatically maintained despite changes in temperature.
A dual tap CCD sensor allows for the image to be split in half (or in 4s for a quad tap sensor) so that the charge transfer can be completed much more quickly (Figure 1). One of the side effects of using a dual tap camera is a channel mismatch. Channel mismatch is visible as a difference in offset, linearity, or sensitivity of the two image haves (Figure 2).
Figure 1: Dual Tap Camera readout
Figure 2: Recombination of 2 imaging channels into the image
Channel mismatch is defined as the contrast between adjacent image planes that originate from a different detector channel. The channel mismatch or the channel matching error is specified under a uniform detector illumination.
Figure 3: Channel interfaces for dual and quad channel area scan sensors
The ratios of the interfaces shown below are considered to produce one channel mismatch specification value.
Some area scan CCD camera manufacturers specify channel-matching error in terms of percentage. Adimec has determined that this is only valid for the area near saturation. When talking about 1 or 2 grey levels, then a percentage is not meaningful. We specify with an absolute value in the lower portion (numbers of grey levels) and at higher grey levels, we specify in a %.
Uniform channel matching is verified over the full exposure range of our cameras. The channel matching is also set to automatically adjust for temperature changes.