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buffer amplifiers solve vco problemsWIRELESS, RF, AND CABLE

Application Note 2019: May 11, 2003

Buffer Amplifiers Solve VCO Problems
Common design practice is to isolate two circuit stages by introducing a buffer amplifier between them. Isolation minimizes many adverse effects, and at radio frequencies (RF). Poor output isolation can disturb oscillator performance, so a buffer stage is often included at oscillator outputs. Before discussing the addition of a buffer amplifier stage, we consider some typical VCO characteristics and how isolation problems can degrade performance. A common problem, for example, is the frequency change exhibited by a VCO in response to varying load conditions (frequency pulling). A change in impedance seen by the VCO output can induce changes in the dc voltages across junctions of the VCO's act