Resonant frequency of a circuit is proportional to sq rt (L x C). A varactor diode, when suitably voltage biased, looks like a capacitor (C). Varying the bias varies the capacitor and thus the resonant frequency .
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I think you you are asking about varactor diode. varactor means variable capacitor. varactor diode is a p-n junction diode which provide a capacitance across it subjected to applied forward and reverse bias. means it provide variable capacitance which depends on the applied reverse voltage(mostly varactor diode works on reverse voltage).They are also known as varicap
The varactor diode is used in frequency tuning applications. Its effective capacitance is a function of the reverse bias voltage across it.
tuned circuit
A varactor diode is most commonly used as the variable reactor. The varactor is a semiconductor pnjunction diode, and its junction capacitance is varied by the application of a steady signal from a local microwave oscillator, called the pump. Amplification of weak signal waves occurs through a nonlinear modulation or signal-mixing process which produces additional signal waves at other frequencies. This process may provide negative-resistance amplification for the applied signal wave and increased power in one or more of the new frequencies which are generated.
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A diode modulator is a type of AM modulator constructed using diodes. One type of diode modulator is the ring modulator shown in the image.
I think you you are asking about varactor diode. varactor means variable capacitor. varactor diode is a p-n junction diode which provide a capacitance across it subjected to applied forward and reverse bias. means it provide variable capacitance which depends on the applied reverse voltage(mostly varactor diode works on reverse voltage).They are also known as varicap
varactor diode is a correct answer
A diode bridge modulator is one kind of balanced modulator.
invented by Arthur Uhlir and A. Bakanowski
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the output from a balanced modulator consists of modulating freq also. this can be eliminated in a diode modulator by adding two more diodes, making a diode ring. therefore called ring modulator
the output from a balanced modulator consists of modulating freq also. this can be eliminated in a diode modulator by adding two more diodes, making a diode ring. therefore called ring modulator
It is called a varactor or a varicap diode. Its capacitance varies nonlinearly with the reverse voltage applied to its terminals.
Short answer: By using a varactor diode as the capacitance in a parallel resonant ckt, by changing the reverse bias voltage you change the value of capacitance which in turn changes the resonant frequency. This makes a tuneable resonant ckt.
The varactor diode is used in frequency tuning applications. Its effective capacitance is a function of the reverse bias voltage across it.