LOW-VOLTAGE DIRECT I Q-MODULATOR AND POWER-AMPLIFIER FOR 2-GHZ TRANSMITTER/

An integrated 1-2 GHz GaAs MESFET direct conversion I/Q-modulator and a power amplifier operating at a supply voltage of 3 V have been desig ned and fabricated. The core of the I/Q-modulator, a 90 degrees phase shifter, is realized with a 2-section 4-phase RC-filter. The YQ-modula tor converts a baseband signal directly to the 1.1-2.0 GHz RF frequenc y. Without any external adjustment, the carrier rejection and the side band rejection are better than 30 dBc and 26 dBc, respectively. The ou tput power of the modulator is -6.5 dBm at a LO frequency of 1.75 GHz and for a baseband signal level of 180 mV (100 kHz). The power consump tion of the YQ-modulator is 200 mW at 3-V supply voltage. The 3-V powe r amplifier is a three stage amplifier having the first two stages bia sed to class A and the last stage to class AB. The maximum output powe r of the three stage MESFET power amplifier is +27 dBm and the maximum available power gain is 32 dB. An external output matching circuit is used to feed the output to a 50 Ohm load. The die sizes of the modula tor and power amplifier are 2.7 x 1.3 mm(2) and 2.0 x 2.0 mm(2), respe ctively. The circuits have been processed with GEC-Marconi GaAs F20 pr ocess.