A veratile amplitude controller is presented, which is intended for phased array applications or QAMmodulators operating directly at the desired radio frequency. Due to the small geometry and the 0.2 pm GaAs/GaALAs HEMTtechnology, a bandwidth from 15 to 60 GHz could be achieved. Coplanar waveguides and lumped elements were used as passive circuit elements. The main topology consists of a differential amplifier and a coplanar balun. The control voltages of the differential amplifier are applied in a push-pull scheme. The balun operates as 1800-power combiner and subtracts both RF-signals. In this way, the comnon mode is rejected and the phase of the out signal changes by 1800, when the amplitude crosses zero.
Flip-chip interconnects with 80 pm bumps are optimized for 38 GHz by means of electromagnetic simulation. Thin-film microstrip is used as transmission-line on the carrier substrate. A compensation structure reduces reflections at the interconnect below -20 dB. Measurements of a passive structure and active chip modules proved feasibility of this approach.
INTROD U CTlONCommercial communication and radar systems in the millimeter-wave fiequency range require costeffective solutions for the front-end multichip modules (MCMs). For this purpose, the flip-chip technique is very attractive in comparison with wire bonding because of the smaller dimensions and the potential for high-volume production (see, e.g., [l], [21,[31).
A monolithic integrated amplifi~r in HFET-Technology for the 27 GHz band is presented, fitteij for. the use in digital radio link front ends with dedicated in-and out-of-band specifications. The amplifier consists of two stages of 0.5 ~m HFETs and some passive circuitry for matching, biasing and gain stabilizing. Coplanar waveguides and lumped elements like thinfilm resistors, MIM-capacitors and spiral inductors were used. All passiv and active components were measured separately and the derived circuit models were placed into a CADlibrary.
A monolithic integrated wide-band amplifier is presented, which consists of two 0.3 pm HEMT-stages in GaAs/GaAIAs-Technology. The main signal path consists of a coplanar waveguide, which interfaces conveniently to the HEMT-cells. A feedback circuit with R, Land C connects gate and drain. To close the feedback loop small scale microstrip lines were combined with CPW /1, 2, 4/. Matching is done with a LC circuit at the gate and a combination of transmission line and capacitor at the drain. In addition there are some other passive elements for biasing, which reduce external components to a minimum. All element models were checked with measured data and placed into a CAD-library for easy use in the design process.
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