A 7-Bit Reverse-Saturated SiGe HBT Discrete Gain Step Attenuator

In this brief, the analysis, design, and measured results of a fully integrated 7-bit step attenuator implemented in a 0.25-μm Silicon-Germanium (SiGe) BiCMOS process technology, are described. The attenuator is designed based on delicately ordered and cascaded Π/T type attenuation blocks, which are comprised of series/shunt switches employing SiGe hetero-junction bipolar transistors (HBTs) with peak f
_T
/f
_max
of 110/180 GHz. HBTs are employed as a series switch to decrease the insertion-loss (IL) of the attenuator. Moreover, to the authors' best knowledge, this is the first study presenting the effect of employing reverse-saturated HBTs as a shunt switch for each attenuation blocks. Thanks to this advancement, the highest input-referred 1-dB compression point (IP
_1dB
) is reported for Si-based similar studies. This method also decreases the IL of the proposed attenuator. The measurements result in the state-of-the-art performance with 28.575-dB attenuation range by 0.225-dB gain steps while maintaining 7-bit amplitude resolution across 6.6 GHz-12.8 GHz frequency band, where RMS phase error remains below 3.3° and IL is less than 12.4 dB. The measured IP
_1dB
of the attenuator is 13.5 dBm while drawing 8 mA from 3.3-V supply. The die occupies an area of 1.37 mm × 0.56 mm excluding pads.