Varactor Diode or Varicap Diode Working and Applications

Varactor Diode or Varicap Diode Working and Applications • What is a Varactor Diode? these diodes are chosen for giving the desired capacitance changes as they are special types of diodes. Varactor diodes are specifically fabricated and optimized such that they permit a high range of changes in capacitance.

Working of a Varactor Diode The volume of the depletion region of the diode varies with change in reverse bias. If the reverse voltage of the diode is increased, then the size of the depletion region increases. Likewise, if the reverse voltage of the Varactor diode is decreased, then the size of the depletion region decreases. Hence, by changing the reverse bias of the diode the capacitance can be changed.

Applications of Varactor Diode 1 It is used in variable resonant tank LC circuit. Here C part is varied using varactor diode. 2 AFC(Automatic Frequency Control) where in varactor diode is used to set LO signal. 3 Varactor is used as frequency modulator. 4 It is used as frequency multiplier in microwave receiver LO. 5 It is used as RF phase shifter.

BJT bipolar junction transistor FET field effect transistor

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Bipolar Junction Transistor (BJT) Field Effect Transistor (FET) Bipolardevice. In BJT, the operation is depends upon both minority and majority current carriers. Thus it is known as Bipolar device. Uni-polar device. In FET, the operation is depends upon the flow of majority carriers only. Ie holes for P-Channel FET and electrons for N-Channel FET. Therefore they are called as Unipolar devices. Lower switching speed. BJT suffers from minority carrier storage effects. So it has lower switching speed and cut off frequencies. Higher switching speed FET does not suffers from minority carrier storage effects. So it has higher switching speed and cut off frequencies. Current controlled device. In BJT, the base current controls the output current. Voltage controlled device. In FET, the Gate voltage controls the output current.

Bipolar Junction Transistor (BJT) Field Effect Transistor (FET) Less input impedance. The input circuit of BJT is forward biased. So BJT has low input impedance. High input impedance The input circuit of FET is reverse biased. So FET exhibits much higher input impedance (>100 Mohms) and lower output impedance. As they have high degree of isolation between input and output, FET acts as a buffer amplifier. Comparatively BJT has more noisy operation. Less noisy FET don’t have junctions and the current conduction is happening through N-type or P-type semiconductor material. So its operation is less noisy. Relatively more affected by radiations Due to reduction in minority carrier lifetime, the performance of BJT is degraded by neutron radiation. Less affected. As FET operation does not depends upon the minority carriers, they can tolerate much higher level of radiation.

Bipolar Junction Transistor (BJT) Field Effect Transistor (FET) Lesser thermal stability. BJT has a positive temperature coefficient at high current levels. It leads to thermal breakdown. More thermal stability. FET has a negative temperature coefficient at high current levels. It prevents the FET from thermal breakdown issue. In IC fabrication, BJTs are occupying more space. FETs are easier to fabricate and occupying less space. BJTs are cheaper to produce. Comparatively FETs are more costly.