Browse Prior Art Database

DYNAMIC RF POWER CLAMP

IP.com Disclosure Number: IPCOM000008404D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-12
Document File: 2 page(s) / 87K

Publishing Venue

Motorola

Related People

Brian Lacy: AUTHOR

Abstract

Many RF Power Amplifiers (PAS) are not very rugged to power output above a certain level. Power out is controlled by software and the control loop. Software is to slow to save the PA from control loop overshoot and the control loop does not know when the software has asked for too much power. Even older PAS whose power out was set by a poten- tiometer could be destroyed by over aggressive technicians. A fast power limit is needed to protect the PA while still allowing the software to control power levels.

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MOTOROLA Technical Developments

DYNAMIC RF POWER CLAMP

by Brian Lacy

PROBLEM

  Many RF Power Amplifiers (PAS) are not very rugged to power output above a certain level. Power out is controlled by software and the control loop. Software is to slow to save the PA from control loop overshoot and the control loop does not know when the software has asked for too much power. Even older PAS whose power out was set by a poten- tiometer could be destroyed by over aggressive technicians. A fast power limit is needed to protect the PA while still allowing the software to control power levels.

  Currently the software controls power out levels and monitors for overpower situations, but it is too slow to respond to transient RF power surges. This power limit can be accomplished with a zener diode at Vref in Figure I, but the zener will not protect the open loop situation or if the control loop has some overshoot. The zener cannot be used if Vref is not accessible as on many power control ICs. This power limit cannot be accomplished with a zener or crowbar clamp on the control voltage as shown in Figure I, because of the wide range of control voltage for a given power out. Overdamped control

loops do not solve the open loop condition. Many radios limit the control voltage, but this voltage limit must be individually set on each radio.

SOLUTION

  The invention limits power out by clamping the power control voltage to a predetermined RF power level as measured by an RF power detector (see Figu...