Understanding Smart Sensors - Nomads.usp

176 Understanding Smart SensorsLegendGaAsTransmit chainTxAntennaswitchRxReceiver chainLDMOSMOSAICPower ampPALow noise ampLNABiCMOSCMOSBIPOLARUpconverterVCOPLLDownconverterRF systemModulationSynthesizerPrescalerA/DIF amp anddemodulatorAnalogDigital systemADPCM and CODECSystemFigure 8.1 RF to digital transition.technologies, depending on the application. The term monolithic microwaveintegrated circuit (MMIC) is used for RFICs in the microwave range.The transition from RF to digital baseband is simplified by mixed-signal,analog-digital ICs. As shown in Figure 8.1, a phase-locked loop (PLL) synthesizerand prescaler, as well as a modulator/demodulator (modem), are requiredfor this transition. PLL frequency synthesizers are required in RF applicationsto provide digital tuning capability for wireless digital communication toimplement a cost-effective, multiple-channel design. A PLL allows a precise stablefrequency to be generated with an MCU controlling the frequency.Advanced CMOS processes provide the lowest power dissipation and a lowoperating voltage for 100 to 300 MHz. BiCMOS increases the frequency range(to about 2 GHz) and provides flexible circuit elements at moderate power dissipation.An advanced bipolar process, like the MOSAIC (Motorola Self-