Silicon Germanium (SiGe) Technology Enhances Radio Front-End Performance - AN697

This application note describes how silicon germanium enhances IC performance in RF applications. A Giacoleto model is used to analyze noise effects. Wider gain bandwidth of SiGe technology is shown to provide lower noise performance. The impact of SiGe on linearity is explored. Three parameters are increasingly important for cellular handsets and other digital, portable, wireless communication devices. Low power consumption and lightweight batteries lend autonomy to the device, higher front-end sensitivity increases the reception distance, and greater frontend linearity has a directimpact on the admissible dynamic range. This last parameter is gaining emphasiswith the advent of nonconstant-energy modulation schemes such as π/4DQPSKand 8QAM. Silicon Germanium (SiGe) is the newest innovation for simultaneously improvingthe power consumption, sensitivity, and dynamic range of a receiver. GST-3 isa new high-speed IC process technology based on silicon germanium (SiGe), whichfeatures a transition figure (fT) of 35GHz. A typical front-end blockdiagram (Figure 1) shows the performance possible with Silicon Germanium technology(1.9GHz) for a combination mixer and low-noise amplifier (LNA). Figure 1. Typical radio input circuitry includes a low-noise amplifier and mixer.