
Active components 51
spaced tuning capacitor except that it is adjusted
by a DC voltage rather than a rotary shaft. Tuning
varactors are designed to have a low series loss r«,
so that they exhibit a high quaHty factor Q, defined
as Xc/n, over the range of frequencies for which
they are designed.
Another use for varactors is as frequency multi-
pHers. If an RF voltage with a peak-to-peak
amplitude of several volts is applied to a reverse
biased diode, its capacitance will vary in sympathy
with the RF voltage. Thus the device is behaving as
a non-linear (voltage dependent) capacitor, and as
a result the RF current will contain harmonic
component ...