Browse Prior Art Database

RF HIGH POWER LINEAR AMPLIFIER LINVRIZER

IP.com Disclosure Number: IPCOM000007307D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-13
Document File: 2 page(s) / 95K

Publishing Venue

Motorola

Related People

Randall J. Clark II: AUTHOR [+2]

Abstract

In our case the problem was that during two- tone testing of our amplifiers (this is one way to gage the linearity of an RF amplifier) a beat fre- quency (f2-fl) developed on the base of the RF devices.

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MOTOROLA Technical Developments Volume 23 October 1994

RF HIGH POWER LINEAR AMPLIFIER LINVRIZER

by Randall J. Clark II and Rodney Hagen

first stage which is a class A common emitter ampli- fier performs two functions. One being voltage gain and the other being phase inversion. The second stage which is a class A emitter follower provides the current gain necessary to drive a low imped- ance load (the biasing diodes Q3 and Q4). The cir- cuit is biased up at class A to minimize the distor- tion the audio amp creates. If the audio amps distortion is high then it will be creating its own noise on the RF bias circuit, thus degrading IM performance.

THE PROBLEM: NOISE ON THE BIAS LINES OF RF DEVICES.

  In our case the problem was that during two- tone testing of our amplifiers (this is one way to gage the linearity of an RF amplifier) a beat fre- quency (f2-fl) developed on the base of the RF devices.

  The resulting problem was that the beat he- quency was changing our predetermined bias point. The bias point we chose placed us in the linear por- tion of the AC load line which allowed us to obtain acceptable IM (intermodulation distortion) per- formance at a given power out and efficiency. If this bias point is changed by the (f2-fl) product then IM will suffer. If the bias point is changed to an ex- treme then clipping or cross over distortion will result which will cause further deterioration of the IM performance.

OPERATION

  The circuit counter acts the beat frequency on the base of the RF device as follows: The base ofthe RF device is sampled at point (A) in the circuit. The signal is AC coupled back to point (B). If any ripple is present at point, (B) then it will be linearly amplified, and phase shifted 180 degrees by stage one of the audio amplifier. Stage two will provide en...