Automatic Amplitude Control Loop for a 2-V, 2.5-GHz LC-tank VCO

The paper discusses the design of the automatic amplitude control circuit (AAC) for wireless-targeted oscillators, presenting a 2-V, 2.5-GHz LC-tank bipolar VCO. Potential phase noise degradation due to the amplitude loop is illustrated, along with design choices to avoid this effect. The circuit manufactured draws 7 mA in the VCO and less than 600 μA in the AAC, with SSCR=-104 dBc/Hz@100 kHz. Once normalized for power, Q-factor and operating frequency, this phase noise performance ranks first among the bipolar VCOs published so far