which is better, a sensor with 12 um or 17 um? - Page 1
Forum section: electronics / general

author: edubz
author_rank: Contributor
timestamp: September 06, 2021, 11:35:38 pm
content: I was at the store the other day testing thermals and the sales rep said 12 it better then 17, I always thought bigger was better, you know bigger size more pixels.maybe he was just trying to sell me the model, or is there any truth to what hes saying?I always thought the AGM with the 384 and 12 um was inferior to pulsars 384 17 um sensors in the camera

author: langwadt
author_rank: Super Contributor
timestamp: September 06, 2021, 11:52:20 pm
content: 12/17 um refers to the size of each "pixel", smaller number means you can have more pixels in the same area and a smaller lenseif one is better than the other I suspect depends and a lot of other things

author: Fraser
author_rank: Super Contributor
timestamp: September 07, 2021, 12:13:12 am
content: The physics of the situation suggests that 17um pixels are better than 12um pixels. The area of the pixel is what collects the thermal energy coming out of the lens system. The wavelength of the energy also plays a part in how well a pixel will perform. The reason that 12um pixels were developed was to decrease the size of the microbolometer die for a given pixel count (VxH pixels). This offers the benefit of reduced fabrication cost and smaller optics. When trying to miniaturise a thermal imaging core the reduction in microbolometer FPA size can also be an advantage, especially when working with VGA or XGA resolutions.When using a 12um pixel microbolometer, noise can be a problem.The actual thermal energy collection area of a 12um pixel is not 12um x12um, it is less than that due to the support structures around the pixel and can be a rectangle rather than a square. The efficiency of the 12um pixel is lower than that of a 17um or 25um pixel so the signal that is fed to the ADC can suffer from poorer signal to noise ratio. The manufacturers of these modern microbolometers do their best to address this S/N ratio challenge and have been successful in creating 12um pixel based microbolometers that produce excellent imagery. When they make 17um or 25um pixel based microbolometers they do not have to work so hard to achieve the desired S/N ratio or they can apply the same techniques as used for the 12um pixel microbolometers and produce very good, low noise, microbolometers.As stated, the 17um and 25um pixel microbolometers are more expensive to produce, due to the larger die size, but I would choose a 17um or 25um pixel over a 12um pixel if given the choice and having funds to afford such. There may be an argument that the 12um pixels based microbolometers are more advanced in their design by necessity so potentially more ‘modern’ than the larger pixel microbolometers but the microbolometer manufacturers are continually improving all of their offerings so the larger pixel FPA will likely also gain from the 12um noise reduction techniques. In the ‘good old days’ the pixels were 35um and 50um ….. nice large thermal energy receptors but the technology within the microbolometers and ROIC was less refined so much of the advantage of larger pixels was likely lost in system inefficiency and internal noise.There is also the matter of VOx vs A-Si pixels …… historically VOx pixels produced more output than A-Si pixels and had a better S/N ratio.A-Si also suffered quite badly with column noise. Over the years, the A-Si microbolometers have been refined and developed by companies like ULIS to produce performance very close to that of a VOx microbolometer. Camera manufacturers use noise reduction and processing techniques to reduce visible noise on both VOx and A-Si based Cameras. They may just have to work a bit harder on A-Si based cameras though. If buying an older A-Si based imaging core, expect to see quite a bit of column noise but they are still good performers and the Raytheon Thermal Eye 2000AS remains a marvel of technology for its time.A final comment on microbolometer performance…… it does not matter how well a microbolomter performs in the lab if it is poorly integrated into an imaging core and camera. Poor optical block design and/or electronics package failings can destroy the performance of the microbolomter. I have seen truly shocking imagery coming from a poorly designed thermal camera that used a decent ULIS microbolomter. The fault lay at the door of the cameras design team and not ULIS.Fraser