how can use Varactor Capasitance Diode?

[baby_1]

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?


Any Help appericated

 

[tpetar]

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.

https://mysite.du.edu/~etuttle/electron/elect40.htm


Varactor Circuits
https://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/circuits.php

https://www.qsl.net/ko6bb/varactor.html

 

[jiripolivka]

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.

https://mysite.du.edu/~etuttle/electron/elect40.htm


Varactor Circuits
https://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/circuits.php

https://www.qsl.net/ko6bb/varactor.html

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.

 

[baby_1]

if the varactor have low Q what component can i use instead of it?

 

[jiripolivka]

if the varactor have low Q what component can i use instead of it?

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.

 

[thannara123]

look here https://electronics-diy.com/electronic_schematic.php?id=1066
https://www.edaboard.com/threads/141197/