Introduction.- Transformer Design and Characterization in CMOS Process.- Design Considerations for CMOS Voltage-Controlled Oscillators (VCOs).- Design Considerations for CMOS Frequency Dividers.- Ultra-Low-Voltage VCO and QVCO Using Transformer Technique.- Magnetically-Tuned Multi-Mode CMOS VCO.- Transformer-Based Injection-Locked Frequency Divider.- Conclusion.