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Questions tagged [varactor]

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2 answers
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Varactor diode simulation behaving opposite than expected

I've been trying to learn about resonance circuits and filters and so forth, intending to try to build some kind of tunable filter or something. I'm running some simulations in KiCAD to help confirm/...
Erhannis's user avatar
  • 187
0 votes
1 answer
102 views

Resonant frequency of a tuning circuit with varactors

This is the circuit that I'm simulating in LTSpice: I measured the experimental resonant frequency of the circuit by finding the frequency at which \$V_\text{out}\$ peaks for different values of \$...
kene02's user avatar
  • 538
0 votes
1 answer
291 views

Changing varactor capacitance based on different frequencies

I am working on a project that uses a varactor diode in a VCO to output a certain frequency. As I understand it, changing the voltage amplitude changes the capacitance of the varactor diode. The input,...
LinHanLee's user avatar
12 votes
1 answer
867 views

Voltage-tunable capacitors -- how do they work, specifically those from Murata?

I'm curious about how MURATA variable capacitors work, for example, parts from the family LXRW0YV330-056. As far as I can tell, these are not semiconductor varactors, but based on some other physical ...
Andrea's user avatar
  • 121
1 vote
2 answers
543 views

Voltage controlled oscillator with a MOSFET

Is it a good idea to use a normal MOSFET as a varactor for a variable signal generator? For example: I have an IRFZ44N and the datasheets says it has an input capacitance of 1470 pF. Can I use that ...
JOHN KARIUKI's user avatar
0 votes
3 answers
525 views

Request for circuit review: varactor-tuned AM radio receiver

I apologize if this is not the place for newbie questions or circuit review requests, but I was hoping for some wisdom on an AM receiver circuit I have sketched out. From left to right it is intended ...
classic_sasquatch_behavior's user avatar
0 votes
2 answers
932 views

Can anyone help me in designing this variable frequency colpitt oscillator?

I am basically trying to achieve a variable frequency colpitt oscillator by using a varactor diode to achieve frequency change. However, I am having trouble figuring out how to connect it so that it ...
needbrainscratched's user avatar
0 votes
1 answer
465 views

What is the equivalent LTSpice diagram of the given varactor diode modulator (FM)

Given below is an example of direct FM generation using varactor diode modulator. What is the equivalent circuit of this in LTspice? Can you explain the given circuit?
Levixten's user avatar
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0 answers
36 views

How can I tell a n channel MOS varactor from a p channel MOS varactor using the CV plot (gate-source capacitance on gate source voltage)?

I couldn't find the differences of the 2 types of varactors (varicaps). I used the CV method and got the curve, but I don't know if I have a n type or p type. How can you tell? How do you calculate ...
Toma's user avatar
  • 155
2 votes
0 answers
320 views

How do you calculate phase shift induced by a shunt capacitor?

Given a simple loaded-line shunt-capacitor phase shifter, how can I calculate the phase shift and insertion loss at S21 caused by the shunt capacitor (varicap in my case, but for any cap) assuming I ...
KJ7LNW's user avatar
  • 2,190
0 votes
1 answer
846 views

Simulating NMOS as capacitor example

I would like to ask your opinion regarding NMOS test-bench as a varactor (voltage control capacitor). I am trying to find the properties of Vg,W for achieving a \$200fF\$ capacitor. Here is my test-...
Daniel Sapir's user avatar
1 vote
1 answer
635 views

Trouble with FSK VCO modulation circuit

Circuit shown is a VCO that reliably creates a 200MHz sine wave at 3V pk-pk. I would like to use this VCO to create an FSK modulated signal. My bit 1 frequency = 200Mhz and my bit 0 frequency = 205Mhz ...
thedamp's user avatar
  • 35
2 votes
3 answers
445 views

VCO circuit Analysis

can you help me with the basic comprehension of this Voltage Controlled Oscillator scheme (it was used in a PLL)? I do not understand why there are two varactors instead of one, and the role of the ...
Kinka-Byo's user avatar
  • 3,550
2 votes
2 answers
2k views

Can Zener or Schottky diodes be used as a substitute for varicap diodes in tuning a VCO?

In particular, this would be a fairly low frequency VCO with a frequency range of 10 Hz to 20 kHz. I'm thinking of the configuration with the T-junction that has 2 opposite facing, reversed biased ...
Mr X's user avatar
  • 734
2 votes
1 answer
778 views

How to choose RF choke in the biasing circuit of varactor-tuned resonant circuit

I am new to circuit and has a very basic question about how to set biasing circuit of varactor. I need to use varactor to tune the resonance behavior of Split ring resonator (SRR) structure when ...
Jingwei Xu's user avatar
0 votes
2 answers
1k views

Direct FM generation using varactor diode

I am trying to generate a constant 1 MHz FM carrier wave. I have achieved it via LC parallel resonance circuit. Initially I let the switch B open and switch A closed, in order to charge the capacitor. ...
Muhammad Naufil's user avatar
0 votes
2 answers
5k views

Changing frequency of 555 timer with varicap or capacitor

I have created a 555 oscillator circuit where the output is set to have flashing LED light. Now I have a problem when I change the voltage of the potentiometer, the output frequency does not change. ...
aguntuk's user avatar
  • 13
0 votes
2 answers
145 views

Capacitive voltage divider with varactor

Is it possible to create a capacitive voltage divider where one of the capacitors is a varactor whose capacitance can be manipulated/varied according to a signal? A varactor is a two port device; what ...
Jordan McBain's user avatar
2 votes
2 answers
139 views

Why are varactors unspecified at 0V?

Specsheets I'm reading tend to specify maximum capacitance at 1V instead of 0V reverse voltage bias. NXP BB series don't show anything below 1V in the tables and 0.5V in the graph. Skyworks SMV ...
Reinderien's user avatar
  • 3,229