High-linearity receivers for mobile communication applications using SiGe technology
FacultiesFakultät für Ingenieurwissenschaften und Informatik
LicenseStandard (Fassung vom 01.10.2008)
This thesis targets receive front-ends with high linearity for applications such as UMTS, CDMA, GPS, TETRA, and WLAN. It reviews available circuit architectures and linearization techniques and chooses the methods best suited for each problem. All circuits have been designed using production line Silicon-Germanium bipolar and BiCMOS processes. Theoretical considerations, extensive simulations and measurements showed that SiGe HBT technology - despite its exponential current-versus-voltage characteristics - offers higher linearity than pHEMT at low current consumption. For a given supply current, the most linear SiGe HBT LNA uses a single-stage cascode design with narrow band reactive load and inductive series feedback. In order to achieve a high 3rd order intercept point (IP3) in the two-tone test, the difference frequency (often called ’beat frequency’) needs to be shorted properly. Different low-frequency termination techniques like broadband source termination, LC trap networks, inductive bias networks and active bias networks based on operational amplifiers have been evaluated and the optimum solution was chosen, depending on the application. For very narrowband applications, cancellation of intermodulation products by using capacitive parallel feedback can be exploited, leading to high IP3. All realised LNAs have been benchmarked with published results and are close to the theoretical optimum in linearity. Both passive mixers and active Gilbert cell mixers have been optimised with respect to linearity. For systems where the interferers appear out-of-band of the SAW filter between LNA and mixer, an optimised Gilbert cell mixer is generally the best compromise in system noise figure, linearity and power consumption. For systems with strong in-band jammer (e.g. professional mobile radio terminals), a NMOS ring mixer with high peak-to-peak LO drive shows high input-referred linearity and allows for high LNA gain resulting in a very low system noise figure.
Subject HeadingsCDMA [GND]
TETRA <Telekommunikation> [GND]