Noise Parameters

Click here to go to our page on noise figure

Click here to go to our page on source pull

Click here for a practical example of using noise parameters 

Click here to see a more complete explanation of noise parameters, including equations! 

Noise parameters are an important concept in designing low noise amplifiers.

The performance of a low noise device is a function of many things:

  • Frequency
  • Bias point
  • Temperature
  • Source impedance
  • Device geometry (number gates, gate width, etc.)

When you measure noise figure on a noise figure meter or noise parameter analyzer, you typically evaluate signal-to-noise ratio (noise figure) while restricted to a fifty-ohm system. At the device level, your low noise transistor is not going to give you the best response at fifty ohms. Measuring noise parameters using source pull is what is used to empirically gather all of the data you need to design a low noise amplifier, starting from the device level.

Further discussion of noise parameters appears on our page on source pull.

Adding noise parameters to manufacturer's S-parameter data

In order to predict noise figure in a linear system, active components that are described by S-parameters must have their noise parameters appended to the S2P file. Check it out, this page has an example of faking noise parameters!

By the way, it stinks that manufacturers don't go the extra mile of putting noise parameters into their S2P files.  If enough of us complain, maybe that will change.  Not that long ago they didn't even provide S2P files as downloads. It's time for a Microwaves101 rule of thumb:


Note to manufacturers: the more data a user has on your products, the more likely he is to use it. As a corollary, the easier it is to obtain your data, the more customers you will have. Per the discussion above, would it be too much trouble to include noise parameters in LNA S-parameters? Also, if you really want to sell SPDT switches, could you post three-port S-parameters? (Readers, look for a future article on faking three-port S-parameters for switches...) Can we please have "cold" S-parameters of all of your active parts? And no, I don't want to register my name to get the data I need...



Author : Unknown Editor