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INTEGRATED LOGIC TRANSLATOR AND RAMP CIRCUIT FOR GaAs POWER AMP

IP.com Disclosure Number: IPCOM000007269D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-08
Document File: 2 page(s) / 83K

Publishing Venue

Motorola

Related People

Tom Schiltz: AUTHOR [+2]

Abstract

System specifications for digital cordless tele- phones require that some form of transmitter burst mask control be implemented to limit out-of-band spurious emissions. For systems that employ constant-envelope modulation schemes such as FSK, GMSK, and GFSK, the burst mask control is easily implemented by ramping the positive voltage sup- ply of the power amplifier in a controlled manner with a discrete power MOSFET.

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MOTOROLA Technical Developments Volume 23 October 1994

INTEGRATED LOGIC TRANSLATOR AND RAMP CIRCUIT FOR GaAs POWER AMP

by Tom Schiltz and Bill Beckwith

1. INTRODUCTION 2. OUR SOLUTION

  System specifications for digital cordless tele- phones require that some form of transmitter burst mask control be implemented to limit out-of-band spurious emissions. For systems that employ constant-envelope modulation schemes such as FSK, GMSK, and GFSK, the burst mask control is easily implemented by ramping the positive voltage sup- ply of the power amplifier in a controlled manner with a discrete power MOSFET.

  To minimize size and weight, the power supply for a typical digital cordless telephone is limited to three NiCd batteries. This produces a 3.6 Vdc typi- cal supply A power MOSFET requires approximately 6 Volts gate-to-source, or 9.6 V at the gate to fully enhance for low voltage drop. A voltage tripler cir- cuit is required to create the 9.6 V control signal from the 3.6 V battery supply.

  We have integrated the ramp circuit on a GaAs power amplifier IC by replacing the discrete n-channel power MOSFET with an n-channel depletion-mode GaAs MESFET In addition, we have designed a low-current logic translator circuit that translates a OV/3V CMOS ramp command signal to a rail-to-rail (Vss/Vdd) level to operate the gate of the power MESFET. The MESFET is fully enhanced when the gate voltage equals the battery voltage; therefore, a voltage tripler is not required.

  A block diagr...