Low-cost silicon-germanium (SiGe) transceivers in the 122-GHz range are on track to eventually serve sensor, imaging, and communications applications. For example, a group of researchers has presented the iterative design of an integrated subharmonic receiver from 120 to 127 GHz. It comprises a single-ended low-noise amplifier (LNA), a 60-GHz push-push voltage-controlled oscillator (VCO) with 1/32 divider, polyphase filter, and subharmonic mixer. The receiver, which is fabricated in silicon-germanium:carbide (SiGe:C) BiCMOS technology, delivers a cutoff frequency (fT) of 255 GHz and maximum frequency of oscillator (fMAX) of 315 GHz. The researchers behind this project are IHP GmbH's Klaus Schmalz, Johannes Borngrber, Bernd Heinemann, and J. Christoph Scheytt together with Silicon Radar GmbH's Wolfgang Winkler and Wojciech Debski.
In their first design, the receiver's differential downconversion gain is 25 dB at 127 GHz with 11 dB noise. The 3-dB bandwidth spans 125 to 129 GHz. The receiver provides an input 1-dB compression point of -40 dBm. It draws 139 mA from a supply voltage of +3.3 VDC. In a subsequent design, the receiver provided 31 dB differential gain and 11 dB noise at 122 GHz. The 3-dB bandwidth covered 121 to 124 GHz. Thanks to integrated bandpass filtering, the receiver boasts a noise figure of 8 dB for the 3-GHz intermediate frequency.
The team used transformer coupling between the LNA and the subharmonic mixer in the 122- GHz receiver together with parasitic coupling effects. As an alternative solution, they also optimized the LNA. In doing so, they obtained RF bandpass-filtering characteristics by the LNA itself. After evaluating receiver and subcircuit chips, they found that the highest conversion gain for the receiver was obtained around 127 GHz. See "A Subharmonic Receiver in SiGe Technology for 122 GHz Sensor Applications," IEEE Journal Of Solid-State Circuits, September 2010, p. 1644.
