Tech Briefs

MMIC Amplifiers for 90 to 130 GHz

Output power exceeds that of prior solid-state amplifiers operating above 110 GHz.

The figure shows two monolithic microwave integrated-circuit (MMIC) amplifier chips optimized to function in the frequency range of 90 to 130 GHz, covering nearly all of F-band (90 – 140 GHz). These amplifiers were designed specifically for local-oscillator units in astronomical radio telescopes such as the Atacama Large Millimeter Array (ALMA). They could also be readily adapted for use in electronic test equipment, automotive radar systems, and communications systems that operate between 90 and 130 GHz.

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These MMIC Amplifier Chips operate in the frequency range of 90 to130 GHz. The final stage of the chip shown at the top contains a twowaypower combiner; the final stage of the chip shown at the bottomcontains a four-way power combiner.

There have been many published articles about MMIC poweramplifier chips and modules that operate at lower frequencies in Wband (75–110 GHz). Such chips typically provide 50 to 300 mW of output power per 0.6 to 1.2 mm of gate periphery of the transistors on the chips, and contain either GaAs or InP high-electron-mobility transistors (HEMTs) or InP heterojunction bipolar transistors. The radio-frequency interconnections on such chips have been primarily made with microstrip transmission lines, which are particularly convenient for large eight-way powercombining networks. For higher frequencies, it may be more beneficial to use grounded coplanar waveguide transmission lines to avoid the added source inductances required in microstrip circuits to provide grounds for the transistors. The present 90–130 GHz MMIC amplifiers are products of an effort to increase the operating frequency of power amplifiers beyond W-band utilizing co-planar waveguide circuitry, while also increasing the number of transistors to be power-combined on a chip (and hence, the maximum output power).