Abstract
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 designed and fabricated. The core of the I/Q-modulator, a 90° phase shifter, is realized with a 2-section 4-phase RC-filter. The I/Q-modulator converts a baseband signal directly to the 1.1–2.0 GHz RF frequency. Without any external adjustment, the carrier rejection and the sideband rejection are better than 30 dBc and 26 dBc, respectively. The output 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 consumption of the I/Q-modulator is 200 mW at 3-V supply voltage. The 3-V power amplifier is a three stage amplifier having the first two stages biased to class A and the last stage to class AB. The maximum output power of the three stage MESFET power amplifier is p27 dBm and the maximum available power gain is 32 dB. An external output matching circuit is used to feed the output to a 50 O load. The die sizes of the modulator and power amplifier are 2.7 x 1.3mm ^2 and 2.0 x 2.0mm^2 , respectively. The circuits have been processed with GEC-Marconi GaAs F20 process.
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