Si/SiGe BiCMOS and RFMEMS in Millimeter-Wave Systems: Reconfigurability and Complexity
Hermann Schumacher, Ulm University, Institute of Electron Devices and Circuits, 89069 Ulm, Germany
Silicon technologies have conquered the radio frequency IC market, and are making dramatic inroads even at millimeter and sub-millimeter frequencies. An advantage often claimed, somewhat automatically, is the cost effectiveness of Silicon - yet with few exceptions microwave and millimeter-wave systems will not have the market volume required to make custom ICs in ultra-scaled CMOS or highly complex BiCMOS less expensive than established GaAs ICs with comparable functionality. The true advantage of using Si based technology over III-V competitors is the ability to realize very complex microwave subsystems on chip, increasingly combining analog and digital functions. With the recent introduction of capacitive RFMEMS switches into a state of the art Si/SiGe BiCMOS process, the range of possibilities is further increased.
The presentation will show examples from the author's group supporting this hypothesis. Single function ICs, in this case low-noise amplifiers and oscillators, can be made band switchable through the introduction of RFMEMS switches. An example is a low-noise amplifier which can be configured to work either at 24 GHz or 79 GHz, allowing frontends capable of addressing short-range automotive radar systems in either band. Similarly, a local oscillator can operate either in systems for the 60 GHz intelligent road transport allocation, or for the 77 GHz automotive radar band, opening up interesting architectural capabilities, as well as opening up a way to millimeter-wave ICs as a commodity and not a custom design.
High complexity and reconfigurability can be combined on one chip, as will be shown for an IC which combines four transmit/receive (T/R) modules for a folded reflect array antenna in Ka band. A combination of CMOS and RFMEMS switches are used to reconfigure the signal direction, thus that the antenna can be used in transmit and receive direction. The combination of four T/R modules alleviates the space problem in millimeter-wave phased array antennas. The four module share common functionality: an I2C bus transceiver allows a simplified control architecture using a serial bus, crucial when scaling the antenna to thousands of elements. Precision reference voltage generation and power-on/voltage drop-out reset circuits are also shared. Each T/R module uses a bi-directional vector modulator, controlled by two eight bit digital to analog converters (DACs) which interface also with the I2C control unit. The circuit equally contains DC/DC converters to generate the necessary actuation voltages for the RFMEMS switches