The performance requirements for signal generators have continued to become more demanding as the quality of receivers and the speed of test have increased in all aspects of communications. The spectrum is becoming increasingly congested, new modulation techniques are being developed, components are advancing in speed and performance, and manufacturing volumes are increasing. The S-Series SGA combines a frequency switching speed of 100 µs with a phase noise of -135 dBc/Hz. This technical note describes the key techniques employed in the synthesizer design which make such a step-change in signal generator performance possible.