OPERATION AND WORKING Varactor diode PPT.ppt
- 3. VARACTOR DIODE • The varactor diode is a semiconductor, voltage dependent variable capacitor also known as varicap or voltacap or epicap or voltage-variable capacitor (VVC) diode. • It is a reverse biased junction diode whose mode of operation depends on capacitance of the junction depletion region. 3
- 4. 4 Working Principle of Varactor Diode • In a P-N junction diode, the depletion region forms a barrier which separates the immobile positive ions on the N side and immobile negative ions on the P-side of the junction. Dielectric conducting plates Depletion region width
- 5. 5 • When a P-N junction is reverse biased majority charge carriers move away from the junction and the number of immobile ions increase. Dielectric conducting plates Depletion region width Working Principle of Varactor Diode
- 6. 6 • Thus opposite charges are stored at the distance of depletion region. Dielectric conducting plates Depletion region width Working Principle of Varactor Diode
- 7. • Thus a reverse biased P-n junction can be compared to a charged ParallelplateCapacitor. • The P and N regions on either side, having low resistance areas due to high concentration of majority charge carriers, act as plates of the capacitor and the depletion (transition) region acts as the dielectric (insulting) medium 7 Fig.4 Working Principle of Varactor Diode
- 8. • The reverse biased P-N junction thus has an effective capacitance, whose value is given by CT=ἐA/WD • Where ἐ = permittivity of the semiconductor material, A = area of junction and WD= Width of the depletion layer 8 Working Principle of Varactor Diode
- 9. • As the reverse bias increases, the depletion region becomes wider which effectively increases the distance between the plates and consequently decreases the capacitance. 9 Working Principle of Varactor Diode
- 10. SDE2205.53 to 54 10 • The capacitance varies with the reverse voltage (VR) as CT α 1/VRn • Where n depends upon doping concentration and varies from 1/3 to 1/2 • Hence we can change diode capacitance by simply changing VR Working Principle of Varactor Diode
- 11. 11 Main applications • Automatic frequency control device • FM Modulator • Adjustable band pass filter • Parametric amplifiers • Harmonic generators • Mixers