LNA performance and cooling? - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 07, 2024, 02:40:01 pm
content: Simple question, is cooling an mmic based wideband LNA going to improve the performance of its sensativity and/or linearity?I was looking through my parts for unfinished projects. I had ordered a .2db noise mini circuts mmic thats hermetically sealed and a couple of ebay thermo electric coolers (small 60 watt ones i think). The idea was to build a really sensative front end for L Band stuff, like radio astronomy and moon bounce. I know NASA uses extreme liquid helium set ups to cool the deep space network, but thats a whole different level than a TEC. I would think if TEC cooling an LNA did anything worth while id see it used much more in the amateur community.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 07, 2024, 04:14:29 pm
content: There is little improvement expected when it comes to linearity. Here it is more likely to make things slightly worse as the amplifiers are made for room temperature and the lower temperature may effect biasing.For the noise, it depends - it may help somewhat, but often not very much. At least for the resistor part it is only the noise power proportional to absolute temperature and thus some 10% for 30 K lower.

author: radiolistener
author_rank: Super Contributor
timestamp: June 08, 2024, 08:06:32 am
content: it depends from temperature, but if you're thinking about liquid nitrogen cooling to get super-duper ultra low noise, most of all it will not give you desired effect, because at some cold temperature LNA may start working out of specification or even can be damaged. And overcooling it may give you opposite effect.If you're want ultra low noise with liquid nitrogen temperature, it needs to use circuit which is designed to work at low temperature.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 08, 2024, 08:16:35 am
content: Cooling is definitely a thing in ultra-low-noise LNAs for astronomy - but that is cooling to cryogenic temperatures, and cooling passives such as filters to reduce their loss too. I've also heard of them being used in satcom and mobile basestations to improve range in areas where you have low traffic (as those areas have far less cells and as a result the range of a single cell must be far greater). That said - devices do shift in operating point, so you can't just take a room-temperature device and operate it at cryogenic temperatures.Depends a lot on what noise you are trying to reduce/what noise dominates. The 1/f noise of devices is usually due to traps and defects in the semiconductors, and you can't fundamentally change that with temperature. But in a lot of RF applications, the devices work above the 1/f corner, so thermal channel nosie dominates, which can be reduced with temperature (though at some point, you will move the 1/f corner so far to the right in frequency that 1/f starts dominating again! This is especially the case with MOSFETs that have boatloads of 1/f compared to BJTs, but afaik mosfets work better at cryogenic temperatures)The modeling of devices at cryogenic temperatures is an active field of research as cryo applications such as quantum computing are becoming more and more of a 'hot topic'. I'll show myself out.

author: mawyatt
author_rank: Super Contributor
timestamp: June 08, 2024, 01:08:45 pm
content: Unlike Silicon bipolar transistors, SiGe bipolar devices work quite well at cryogenic temperatures, see IEEE paper below and the work by J Cressler at Georgia Tech, S Weinreb at JPL as well as J Bardin PhD Dissertation at Cal Tech.https://www.ihp-microelectronics.com/php_scripts/publications/manuscript_files/ruecker-ieee-bctm-2017-accepted-2019.pdfWe provided J Cressler at GT various IBM 8HP and 9HP SiGe devices and S Weinreb at JPL a few IBM 8HP SiGe devices that were utilized in Radio Astronomy LNAs.A single TEC stage is usually limited to ~40C delta T, thus one needs to stack the devices which requires significant power to achieve only modest delta Ts, as each stage needs to "pull" the heat produced from the previous stage as total power consumption grows geometrically.LN2 is usually available and likely a better use candidate for a cooled LNA than a stack of TEC devices which will take considerable power and be expensive to achieve a similar temperature (77K).Anyway, interesting project, keep us posted on your progressBest,

author: coppercone2
author_rank: Super Contributor
timestamp: June 08, 2024, 03:11:28 pm
content: I think the problem will be humidity. My suggestion is to shell out on whatever non intrusive humidity control features you can get in order to avoid sealantsfor a summer time engineering thing its probobly going to be annoying to deal with that

author: rfclown
author_rank: Frequent Contributor
timestamp: June 10, 2024, 12:50:11 am
content: I used a SKY67153-396LF for a 1542 MHz LNA at work which is a GaAs pHEMT MMIC. The NF at room temperature was 0.25 dB. I don't remember the number, but I measured it also at -40C and there was a noticeable improvement. I just looked up the datasheet, and they show the NF over temperature for 2.2-3.0 GHz.

author: kiranshila
author_rank: Newbie
timestamp: August 13, 2024, 12:17:19 am
content: I'm almost done with my PhD at Caltech with Sandy Weinreb (mentioned here) on room-temp LNAs. It's an active area of research for large N radio telescope arrays because the cost of cryogenics don't scale compared to the sensitivity from a larger array. I'm working on a TEC-cooled amp right now and the trickiest thing is condensation freezing. We have a harder problem than you because I'm cooling a single wirebonded chip using a 1mm^2 cooler! Typical improvement for HEMTs is about 1K of noise for every 40C, so you need quite a lot of cooling to have an appreciable effect. As mentioned before me, this gets into requiring a multi-stage cooler and quite a bit of power, but it still beats the pants off a cryogenic system.

author: coppercone2
author_rank: Super Contributor
timestamp: August 13, 2024, 01:38:31 am
content: lmfao there is no requirement for a freight elevator to transport 55 gallon drums of liquid nitro and oxygen sensors when you go with TECbut the price of a project goes up by what, 5000%

author: mawyatt
author_rank: Super Contributor
timestamp: August 13, 2024, 02:24:28 am
content: Quote from: kiranshila on August 13, 2024, 12:17:19 amWe used a Split Cycle Stirling Cooler to get a HgCdTe 8-12um IR detector down to ~70K, the cooler was about the size of a soda can. This was used in the XM21 Remote Sensing Chemical Agent detector back in the early 80s. Since intended for battlefield use (went to production), LN2 wasn't an option and TEC was more power hungry at the time, so the Stirling Cooler was selected which introduced its own set of problems, like vibration, reliability, cost and so on!!The IBM BiCMOS SiGe Bipolar devices we mentioned earlier perform better when cooled unlike traditional Si Bipolar devices. They had many benefits over Si devices early on including CMOS, however the never ending node reduction of CMOS with FinFETs and GAA (Gate All Around) have limited SiGe to more of a speciality technology.BTW early congrats on your PhDBest,

author: LM21
author_rank: Regular Contributor
timestamp: August 13, 2024, 01:23:53 pm
content: This is interesting. An off topic questions, sorry.Does it really help to get noise much lower, when any loss on filters, cables and so on, before LNA, adds directly to noise figure.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 13, 2024, 03:40:22 pm
content: If needed fitlers can also be cooled and if critical one keeps the cables to a minimum, with not too many connectors. It depends really on the application if the cooling is worth it. In more simple cases a better antenna can be the easier way. When already using a high end antenna, cooling the amplifier can be well worth it.