A 5–45 GHz linear voltage controlled attenuator MMIC in 3×3-mm plastic package

This paper presents the first pass design and performance of a broadband (5-45 GHz) variable attenuator MMIC in a small SMT package. The attenuator is fabricated using a commercially available 6-inch 0.5 μm GaAs PHEMT technology, and assembled in a standard surface mount plastic QFN (Quad Flat Non-leaded) 3×3 mm package. While occupying a chip area of only 2.34 mm², this packaged attenuator exhibits more than 35-dB dynamic range, with a nominal insertion loss ranging from 1- to 7 dB over the 5-45 GHz frequency band. The key linearity requirements over broadband operation were addressed by mean of distributed multi-gate FET technique. This enables to achieve a high input power compression (P1dB> +20 dBm), with excellent linearity (IIP₃ > +30 dBm) at all attenuation levels. To the author's knowledge, these results are among the best in term of combined bandwidth, insertion loss, dynamic range, and linearity performance, reported for single-chip variable attenuators in plastic packages. The excitation and suppression of higher order parasitic modes in plastic QFN packages are also discussed.