Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

LNA Predistorsion

LNA Predistorsion

LNA Predistorsion


I´m designing a LNA for an FM receiver. I need 60dB of IMR3 due to customer requirement. In order to achieve that high req. I used a diode in the input of the amplifier as a predistorsion method. It really works for intermodulation, but I have doubts about noise. Does anyone know if this is a good solution? What is the impact on noise of this diode in the input of the amplifier?


RE: LNA Predistorsion

Are you saying that you can count on the distortion caused by the diode will be undone by the LNA first transistor?  This sounds like a schoole problem, not something an engineer would do.  Or am I out of touch with the state of the art in high linearity LNA's?  

I have hear of using the same transistor as a diod and running the same bias through it and thermally connecting the devices to get some semblance of match.  But a match to cancle below 60 dB level sounds like an uberEngineer job.

Good luck.  I will monitor this thread for reports of your success and advice of others.  This should be interesting.

Merry Christmas.


RE: LNA Predistorsion

I am surprised that it works at all.  Being an LNA, I assume you are receiving a very small signal.  That small signal would not swing the diode current very far, and therefore you will have a pretty linear I-V curve--i.e. NOT what you want to generate predistortion.  You want I = V^3.

I guess the answer to your question revolves around what the diode dynamic resistance is.  If you are biasing it up so it only has an ohm or two of resistance, then it will probably not screw up the NF.  If it is acting like a 200 ohm resistor, forget about calling it a LNA!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close