Editing Varicap (section)

==Harmonic multiplication==
In some applications, such as [[Frequency multiplier#Varactor diode|harmonic multiplication]], a large signal amplitude alternating voltage is applied across a varicap to deliberately vary the capacitance at signal rate to generate higher harmonics, which are extracted through filtering.  If a sine wave current of sufficient amplitude is applied driven through a varicap, the resultant voltage gets "peaked" into a more triangular shape, and odd harmonics are generated.

This was one early method used to generate microwave frequencies of moderate power, 1&ndash;2&nbsp;GHz at 1&ndash;5 watts, from about 20 watts at a frequency of 3&ndash;400&nbsp;MHz before adequate transistors had been developed to operate at this higher frequency. This technique is still used to generate much higher frequencies, in the 100&nbsp;GHz &ndash; 1&nbsp;THz range, where even the fastest GaAs transistors are still inadequate.