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REDUCE INSERTION LOSS IN GAAS FET RF SWITCH USING NEGATIVE VOLTAGE DERIVED FROM RF OUTPUT

IP.com Disclosure Number: IPCOM000009872D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-25
Document File: 2 page(s) / 98K

Publishing Venue

Motorola

Related People

Simon Jones: AUTHOR

Abstract

The effect of Lower Control Voltages on insertion loss in GaAs Fet RF antenna switches is mitigated using a negative voltage derived from the transmitter output.

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This is the abbreviated version, containing approximately 50% of the total text.

MOTOROLA

Technical Developments

REDUCE INSERTION LOSS IN GAAS FET RF SWITCH USING NEGATIVE VOLTAGE DERIVED FROM RF OUTPUT

by Simon Jones

ABSTRACT

The effect of Lower Control Voltages on insertion loss in GaAs Fet RF antenna switches is mitigated using a negative voltage derived from the transmitter output.

INTRODUCTION

GaAs FEr RF switches are widely used in many portable radio products for their low cost and ease of use/implementation. However, with today's modern radio products operating at lower and lower supply voltages, the performance of these devices becomes compromised.

Their operation at higher power levels is directly proportional to the control voltages available. The result of this is increased insertion loss in the transmit path, resulting in the need for extra RF power to be generated. This causes greater temperatures, higher current consumption, and a corresponding reduction in battery life.

This paper describes a simple method for recovering this lost peIfonnance even at low power supply voltages.

PROBLEM TO BE SOLVED

Traditional antenna switch designs use pin diodes, with the classic 1/4 wave track to effect antenna changeover between Transmitter and Receiver paths. To simplify and reduce the cost of low tier radio designs, a GaAs Fet RF Switch was used. However, with radios which use 3 and 4 battery cells, the voltages available to operate these switches can be 3V or less. The problem encountered was that even though the devices are rated typically to 2Watts with only 3V available, at power levels above 500mW the insertion loss increases rapidly to greater than I.OdB, from a spec of less

Motorola. Inc. 2000

than 0.2dB. Also, the isolation to the unselected Receive port is reduced to typically 7dB from a specification of >20dB. For a 1 Watt Power Amplifier this results in a power loss of typically 200mW, which can eliminate any 'head room' present in the design, and reduce Power Amp efficiency significantly.

PROPOSED SOLUTION TO THE PROBLEM

The type of switch mentioned above is generally operated using two control lines. One line has >3V applied to it, with the other being taken to OV. To select the...