DESIGN OF LOW NOISE AMPLIFIER

[halmstad]

hi to all im doing thesis of designing of low noise amplifier at 1420 mhz with noise factor 0.5 db. i dont know how to do ,so can u tell me how to start and which transistor is useful for my specifications and i have selected ATF-34143 but it is not stable at 1420 mhz can u telll me how to stabilize the transistor at desired frequency and b/w some range.




thank you


email:avr_aitha@yahoo.co.in

 

[khouly]

first of all u need to read gonzalez book , and read about matching for stability to know how
but simply u need to draw the source and load stability circles and u must be sure that the amp is stable

khouly

 

[John_li]

First you should know whether the transistor that you need is stability.And if it is unstability,you can use the feekback tech. or add a resistor in the drain. to make sure of K>1 and delta<1

 

[VSWR]

There is an excellent tutorial and step-by-step instruction here:

**broken link removed**

 

[Grig]

Hi
Amp which is unstable in the reason of s-parameters based stability factors is may be testable amp realy, but we shoul use it accurately
I think

 

[halmstad]

hi im designing LNA(freq:1420MHZ,NF:0.5db) in this first i selected ATF-55143 transistor and stabilized at 1420MHZ frequency then how can i find input and out put matching networks if u know plzzzz email to my id avr_aitha@yahoo.co.in

 

[khouly]

frist of all , in LNA u need to design input matching network for minimum noise , so with the simulator get Rsopt "which is an optimum source impedance for the amp to get NF min " , then design a matching network to transform the 50 ohm to the desired Rs opt

the ouput matching is to achive max power , so u need to do power matching

khouly

 

[halmstad]

DESIGNING OF LOW NOISE AMPLIFIER[/b]

hi to all im designing LNA at 1420 MHZ for 0.5 db NF ,i have choosen atf 55143 transistor and i simulated then i got the NF 0.7, and stabilization is 1.392 by using a drain resistor but the problem is when i connect input and output matching networks to the transistor it is showing NF is 1.5 db. so can u suggest me how to decrease the noise factor.

 

[khouly]

the input matching network should be optimized for minimum noise
so u have to get the Ropt , which is the optimum source impedance then design the input matching circuit such that transform the 50 ohm to the Ropt


khouly

 

[strennor]

0.5dB NF?
Is it mission impossible?

 

[khouly]

no , the discrete components can reach this , there are some PHEMTs , and HJFETs can give u this NF

khouly

 

[drabos]

0.5 dB noise figure is very common

Think the LNB (staellite broadcast communication), in any television shop you can buy a 0.2-0.3 dB noise figure LNB. (it works at 10-12 GHz)

 

[halmstad]

hi khouly

thank you for your information.my doubt is can we use RC matching networks for input and output matching.

 

[kevinding]

for the LNA, input match muse be done with noise, not gain

 

[khouly]

in RF circuit it isn't recomended to to use RC matching networks , coz the R will add a much noise specialy if it is in the input
it is usually done by LC matching network , check on gonzalez book

khouly

 

[wasm]

0.5 dB noise figure is very common

Think the LNB (staellite broadcast communication), in any television shop you can buy a 0.2-0.3 dB noise figure LNB. (it works at 10-12 GHz)

I disagree 0.2-0.3 dB refers to the LNB not to the LNA at the input of the LNB

The LNB as first element has an horn that is an element with gain and low losses

--> so in the Friis formula the first low noise gain block is the horn not the LNA

0.2dB@10GHz in a LNA is not so simple as you can think ;-)

 

[khouly]

the LNB is a system LNA mixer filter , and IF amp this system NF is .5dB and some times reach .4dB , for thr complete front end

khouly

 

[wasm]

the LNB is a system LNA mixer filter , and IF amp this system NF is .5dB and some times reach .4dB , for thr complete front end

khouly

You are forgetting the horn at the input of the LNB:

horn, LNA, mixer ...

 

[khouly]

the main noise figure come from the LNA when u do system analysis the first component of the system is the key component which affect the noise figure

khouly

 

[wasm]

You are rigth, the key component is the first one, but in a LNB the first element is the horn not the LNA!!!