MMIC phase shifter example 2

Updated December 31, 2009

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This picture of a GaAs MMIC was donated by Liam Devlin of Plextek, from his earlier days at the now defunct Marconi Company. This design is an outstanding example of a digital phase shifter. It is designed for C-band and has six bits. From left to right the bits are 22, 11, 180, 6, 90, 45, which is obvious if you ever designed a digital phase shifter on GaAs but admittedly this is a pretty small club. Click the image to see more detail. The 45, 90 and 180 are switched network high-pass/low-pass designs using an awesome series/shunt switch FET combination for superior isolation of the unwanted path. The lower bits are a form of high-pass/low-pass design which was fully described later in a paper by Campbell and Brown of TriQuint in the December 2000 IEEE MTT transactions paper titled A compact 5-bit phase-shifter MMIC for K-band satellite communication systems. You can learn a lot from this ancient Marconi MMIC design, which can be scaled to your particular frequency and save you weeks of design time. We'll spend some time picking apart the details later. It's hard to improve on this layout, but we would have suggested bigger DC pads if we had been invited to the design review back in the prior century. And what's with that "extra" pad that's labeled "8"? It's a blank pad to recycle an existing probe card! It would have made a nice spot to bring in DC ground at wafer test. Thanks Liam!