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Design >> RF Design >> Reducing PA distortion
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Message started by analogy on Aug 31^st, 2015, 8:11pm

Title: Reducing PA distortion
Post by analogy on Aug 31^st, 2015, 8:11pm

Hypothetically one can reduce PA distortion either via negative feedback or using a filter between PA and antenna (speculating the latter half).

Which method is commonly used to reduce PA distortion and why ?
Thanks.

Title: Re: Reducing PA distortion
Post by aaron_do on Sep 1^st, 2015, 5:25pm

Hi,

typically neither method is used.

Although there are negative feedback based power amplifiers, they're not very common because (also speculating) they represent a heck of a design challenge. In order to optimize performance, power amplifiers need to operate close to their stability and reliability limits. So you can imagine that adding a path from output to input could lead to problems if the circuit and layout modeling is inadequate.

Filtering only works if there is only one frequency channel being used as so far there aren't any good tunable RF filters on the market (good research project?). That rules out Wifi, Mobile and Bluetooth. Also, filtering removes the sidebands, but doesn't improve SNR, so its use is limited.

The most common way to reduce PA distortion is simply to back-off the PA (i.e. transmit at a lower power than it is capable of). But there are plenty of methods such as pre-distortion, cartesian feedback etc which have applications.

regards,
Aaron

Title: Re: Reducing PA distortion
Post by loose-electron on Sep 2^nd, 2015, 12:55pm

frequently it is a multitude of methods, and depends on the PA architecture. Filters, feedback, predistortion, optimize bias point with power level, and others. Research time. IEEE MTT and IEEE JSSC