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New2EEWorld Post subject: LNA amplifier, please Help Unread post
Posted: Thu Feb 03, 2005 6:35 pm Offline Lieutenant Joined:
Thu Feb 03, 2005 6:20 pm Posts: 2 I'm trying to desing and build
a simple multistage LNA? Here are some of the considerations.
frequency desire: 10ghz Fn= 2db or less if possible. Which component
(discrete,bjt, FET, etc) will be the best one and why will i choose
it versus other ones. Cost, etc? (component selection recommendations,
the best in the industry) What other things should i consider for
actually builiding one at home with limited equipment? Temperature
estability consideration or drift? Distortion or liniarity consideration?
( additional circuits to consider) And what shareware software do
you guys consider to be easily accessible and easy to use? I appreciate
any help or comment or feedback, thank you! Top Profile
Bulldog not a Poodle Post subject: Unread postPosted:
Thu Feb 03, 2005 9:43 pm ok what is the application?
why is it at 10GHz/2dB NF/etc...and why are you building it at home?
Top Joe Post subject: LNA Unread postPosted:
Thu Feb 03, 2005 9:50 pm You want either a MESFET, pHEMT, or
HJFET. <<2dB NF possible at 10 GHz. Working at home you
will need a packaged device. This won't be a trivial project at home.
Try NEC (CEL), MwT, Eudyna, Filtronics. Mouser handles NEC, this
may be easier. You should also check the amplifier vendors listed
on this site for a MMIC that meets your requirements. Linearity
and distortion will depend on the bias conditions and the input power.
Gain variation over temperature is -.015dB/degree C as a rule of
thumb for each stage. Check the following site for some useful
application notes. https://www.cel.com/eng/eng_notes.asp I
don't know what shareware is available. Perhaps others have suggestions.
Top Guest Post subject: Shareware Unread
postPosted: Fri Feb 04, 2005 9:05 am Ansoft offers a student
version of their software "serenade". It is a full fuctional and has
most if not all of the functionality of their full version. You will
be limited in the number of components you can use , but if your just
designing a LNA, you should not have a problem. You can find a link
on RF Cafe under the "software" banner. I would recommend downloading
it. It really the only way you will ne able to effectiviely design the
amplifier. Of course, the other alternative is to spend $5 , or so,
and purchase a MMIC, packaged LNA. Hittite microwave corporation has
a packaged LNA that will give <2dB of noise figure from 9 to 17GHz.
I believe the model nimber is HMC516LC5. Top
New2EEWorld Post subject: LNA amplifier, please Help Unread postPosted:
Sat Feb 05, 2005 1:58 pm Offline Lieutenant Joined: Thu
Feb 03, 2005 6:20 pm Posts: 2 Thank you for your feedback. I
appreciate the useful information. I also had other question starting
with: Device: Using a bipolar device (BJT or other), Why isn't
this a prefer choice? Do they offer a bad respond at this prefer frequency?
Why is MESFET, pHEMT, or HJFET a better choice? Is it the NF value that
makes them preferable over others at higher frequencies? Is this the
limitations of our technology today? Design: I will be testing
a combination of different topologies performance for the best LNA.
From MNA & MGA, MNA & MNA, and MNA & LNA. I understand the
MNA & MNA will be preferred because of the best NF value. Is this
also true for practical purposes? Should I consider other configurations?
General: In your opinion, what would be considered a “good” or
“best” performance for a LNA design at 10GHz? (In terms of its specs:
gain, NF, input versus output, etc) What topologies would you choose
and why? (a simple approach) Problems: What problems do you
think I will encounter or should consider looking into when designing
and simulating or hands on testing? Top Profile
IR Post subject: Unread postPosted: Sun Feb 06, 2005 11:09
am Channel devices are by definition less noisy than BJT's because.
You can have many problems that are related to design or layout
of the LNA. Problems like stability, poor linearity etc. When you design
the LNA, You should choose a device that gives you the noise circles
and the minimum noise figure data together with the optimum reflection
coefficient in the source to achieve this noise figure. Most LNA and
transistor manufacturers provide this information for low noise transistors/amplifiers.
You can always find design hints in the application notes for the
transistors you choose. Good luck, IR Top
Joe Post subject: LNA Unread postPosted: Sun Feb 06,
2005 4:50 pm At higher frequencies, the MESFET has lower noise
figure than BJT's. Below 500 MHz the 1/f noise will dominate and the
BJT will have better noise perormance. The HJFET or pHEMT are similar
in structure to the MESFET, but the epitaxial layer structure is different.
Without getting into a discussion in device physics, the resulting structure
has beter gain and noise properties than a regular MESFET. Best
performance for narrow band at 10 GHz <1dB NF Best noise figure
will result from a reactive input match to meet the NFMIN on the Smith
chart. Using 2 devices in a balanced configuration will improve
VSWR. I don't understand what you mean by "MNA & MGA, MNA &
MNA, and MNA & LNA" Stability will be a major consideration.
The LNA isn't much good if it's oscillating. Check out of band.
Top Bulldog not a Poodle Post subject: Unread
postPosted: Mon Feb 07, 2005 1:08 pm try the NEC GaAsFET NE700/710.
I think a 2dB NF is very hard to achieve @ 10GHz. Having viewed the
datasheet if you have any problems do let us know Top
Joe Post subject: NE710 Unread postPosted: Mon Feb 07,
2005 3:03 pm The NE710 was a workhorse MESFET in the amplifier
world 15-20 years ago. It was discontinued about 8 years ago. It is
probably still available from suppliers that specialize in obsolete
parts, but the cost will be $many. This may be good for an existing
design, particular where the design has been qualified in a military
program and cannot be changed without requalification. A new
device from NEC with better performance is available for $2 to $3.
The NE321 has an NFMIN of .32dB @ 10 GHz. Follow this link to the
data sheet. https://www.cel.com/pdf/datasheets/ne3210s1.pdf
Posted 11/12/2012
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