Silicon-Based Ultra-Wideband Beam-Forming

Ultra-wideband (UWB) beam-forming, a special class of multiple-antenna systems, allows for high azimuth and depth resolutions in ranging and imaging applications. This paper reports a fully integrated UWB beam-former featuring controllable true time delay and power gain. Several system and circuit level parameters and characterization methods influencing the design and testing of UWB beam-formers are discussed. A UWB beam-former prototype for imaging applications has been fabricated with the potential to yield 20 mm of range resolution and a 7deg angular resolution from a four-element array with 10 mm element spacing. The UWB beam-former accomplishes a 4-bit delay variation for a total of 64 ps of achievable group delay with a 4-ps resolution, a 5-dB gain variation in 1-dB steps, and a worst case -3-dB gain bandwidth of 13 GHz. Overall operation is achieved by the integration of a 3-bit tapped delay trombone-type structure with a 4-ps variable delay resolution, a 1-bit, 32-ps fixed delay coplanar-type structure, and a variable-gain distributed amplifier. The prototype chip fabricated in a 0.18 mum BiCMOS SiGe process occupies 1.6 mm² of silicon area and consumes 87.5 mW from a 2.5-V supply at the maximum gain setting of 10 dB