A 0.7-3 GHz GaAs QPSK/QAM direct modulator

Abstract

A single chip I/Q direct modulator for use in digital radio links is presented. This device translates directly the phase and quadrature baseband signals to a microwave frequency that can be chosen between 700 MHz and 3 GHz avoiding the use of IF circuits. It is able to generate any type of digital modulation as QPSK, n-PSK, n-QAM, GMSK, etc., with band-limited spectrum. The bandwidth of the I/Q modulating signals is more than 500 MHz allowing the use of the circuit even in the highest capacity systems. The device has 120 components in a 2.2*2.4 mm chip and has been fabricated using 0.5 mu m GaAs MESFET process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>