Hello
how to use Varactor Capasitance Diode? because it has some parameters that i don't know what they do..
could you give an example on Varactor Capasitance Diode datasheet parameters?and how can work with them?
A varactor is also known as a variable capacitance diode or a varicap. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range.
A varactor is also known as a variable capacitance diode or a varicap. It provides an electrically controllable capacitance, which can be used in tuned circuits. It is small and inexpensive, which makes its use advantageous in many applications. Its disadvantages compared to a manually controlled variable capacitor are a lower Q, nonlinearity, lower voltage rating and a more limited range.
There are two kinds of variable-capacitance diodes. One is the "varicap", a tuning element used in place of a variable tuning capacitor in resonant circuits. In receivers the varicaps can be matched in pairs or quads, to form variable center-frequency band-pass filters.
The second type is "step-recovery diode" or SRD. In its P/N junction, one half-wave of a sinusoidal signal is rectified like in a peak detector; in the other half-wave the accumulated charge is released. Varactor diodes are high-reverse-voltage devices, with a wide variation of capacitance; the step recovery generates a huge short power impulse full of harmonics. Varactors can be used in parametric frequency multipliers and converters; they operate with a high efficiency but often at a very narrow band. A typical microwave doubler can have 6 dB conversion loss, a tripler, 9 dB, a quadrupler, 12 dB. Years ago I designed and built a varactor quadrupler delivering ~ 30 mW over a wide W-band frequency range.
Now SRD varactors are forgotten, replaced by active frequency MMIC multipliers. MMIC devices are wideband which generates a high noise level, problem in low-noise receivers.
I do not know what Q you expect. Typical AM and FM tuning varicaps perform as well as air variable capacitors, and the circuits do not show equal performance.
If you bias the varicap above 3-5V (most operate up to 30V), its Q is high enough. You can use a series capacitor to improve circuit Q, with a narrower tuning range.
---------- Post added at 17:55 ---------- Previous post was at 17:54 ----------
correction: the circuits do show an equal performance.