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Method for a protection circuit for a CMOS power amplifier

IP.com Disclosure Number: IPCOM000020405D
Publication Date: 2003-Nov-19
Document File: 3 page(s) / 331K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a protection circuit for a complementary metal oxide semiconductor (CMOS) power amplifier. Benefits include improved functionality and improved reliability.

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Method for a protection circuit for a CMOS power amplifier

Disclosed is a method for a protection circuit for a complementary metal oxide semiconductor (CMOS) power amplifier. Benefits include improved functionality and improved reliability.

Background

         A conventional application is comprised of a simplified RF power amplifier (PA) incorporating a MOSFET device (see Figure 1), designated as M1, with the following additional elements (see Figure 2):

•         Input matching elements: capacitor C1 and inductor L1
•         Output matching elements: inductor L2 and capacitor C2

•         DC blocking capacitor C3

•         Bias choke (large inductor) L3

         Vbias (gate bias voltage) and resistor R1 establish the bias current in M1. C4 is a radio frequency (RF) bypass capacitor at the top of L3. M5 is typically a switch. Current sensing means M2 forms a current mirror with M1, measuring a scaled version of M1’s drain current (Id1) current. Voltage sensing means R2 and the current mirror, M3-M4, substantially sense the drain-to-source voltage (Vds1) of M1. These signals are examined separately and/or in combination. In combining means, they produce control voltage V3. When V3 exceeds a predetermined value known to cause reliability problems, control amplifier A1 (typically a high-gain op amplifier) regulates M5 to lower the supply voltage, Vdd’, to reduce the fault condition to M1 by lowering the signal swing and output current. Alternatively, but not shown, control amplifier A1 could reduce Vbias separately or in addition to reducing Vdd’.

Description

         The disclosed method is a protection circuit for CMOS power amplifiers (PAs) by sensing conditions that would cause device failure and/or reliability problems. These conditions include but are not limited to:

•         Excessive current

•         Excessive voltage

•         Excessive temperature

•         Hot electron affects, such as a shift in threshold voltage resulting in a reduction of gain and/or output power.

         These fault conditions are sensed with appropriate circuitry and used to reduce the supply voltage to the amplifier, Vbias, or both to lower the output power and the fault condition.

         The disclosed method includes fault sensing means that can be used in addition to or instead of some of the previously described protection circuitry. The method adds substrate current sensing means comprising control amplifier A2...