Editing Colpitts oscillator (section)

===Oscillation amplitude===
The amplitude of oscillation is generally difficult to predict, but it can often be accurately estimated using the [[describing function]] method.

For the common-base oscillator in Figure&nbsp;1, this approach applied to a simplified model predicts an output (collector) voltage amplitude given by<ref>Chris Toumazou, George S. Moschytz, Barrie Gilbert. [https://books.google.com/books?id=VoBIOvirkiMC&dq=the+tank+voltage+amplitude+is+calculated+to+be&pg=PA568 Trade-Offs in Analog Circuit Design: The Designer's Companion, Part 1].</ref>

:<math>
V_C = 2 I_C R_L \frac{C_2}{C_1 + C_2},
</math>

where <math>I_C</math> is the bias current, and <math>R_L</math> is the load resistance at the collector.

This assumes that the transistor does not saturate, the collector current flows in narrow pulses, and that the output voltage is sinusoidal (low distortion).

This approximate result also applies to oscillators employing different active device, such as [[MOSFET]]s and [[vacuum tubes]].