Autor: Rufus P. Turner
Editura: Howard W. Sams & Co., Inc., Indianapolis, Indiana
Printed in the United States of America
An aparitie: 1966
Ce sunt diodele varactor / varicap?
Dioda varactor sau varicap este o dioda speciala care are caracteristica de a-si modifica capacitatea interna pe masura ce variaza tensiunea aplicata la borne. Avantajul diodei varivap (varactor) fata de un trimer sau un condensator variabil este ca putem realiza reglaje foarte fine si putem obtine chiar capacitati foarte mici.
Fiecare dioda varicap este contruita pentru a accepta o tensiune maxima bine definita (12V, 25V, 23V s.a.). Pentru a face etajul unui oscilator mai stabil (circuitul LC), se prefera montarea diodelor varicap (varactor) la capetele bobinelor de reglare.
Deci o dioda varicap (sau dioda capacitiva) inlocuieste un condensator variabil si putem realiza oscilatoare sau circuite rezonante mult mai stabile.
Dioda varicap (varactor) este o dioda polarizata invers in care zona de trecere din jurul jonctiunii PN se comporta ca un condensator cu capacitate electrica variabila. Acest lucru este posibil deoarece zona de trecere este formata din doua straturi incarcate electric cu sarcini electrice opuse (ionii ce apar in cei doi semiconductori). Modificand tensiunea inversa aplicata diodei se modifica grosimea zonei de trecere, deci se modifica capacitatea electrica a diodei.
Structura lucrarii
CHAPTER 1 – BASIC VARACTOR THEORY
- What Is a Varactor?
- Varactor Semiconductor Fundamentals
- The PN Junction
- Junction Operation-Inside The Varactor
- Varactor Ratings
- Types of Varactors
CHAPTER 2 – VARACTOR OPERATION
- Voltage and Current Response
- Multiple Operation
- Varactor and Conventional Capacitor in Combination
- Varactor Tuned Circuits
- Varactor As Frequency Multiplier
CHAPTER 3 – RECEIVER APPLICATIONS
- Tuning Requirements and Considerations
- Automatic Frequency
- Control-R-F Amplifier (Preselector)
CHAPTER 4 – TRANSMITTER APPLICATIONS
- Tank Tuning
- Frequency Multipliers
- Frequency Modulation
- Amplitude Modulation
- R-F Output Control
CHAPTER 5 – VARACTOR AMPLIFIERS
- Basic Principles
- Resonant-Slope
- Amplifiers
- Parametric Amplifier
- D-C Amplifier
CHAPTER 6 – INSTRUMENT APPLICATIONS
- Absorption Wavemeter
- Remote Tuned Field-Strength Meter
- Harmonic Intensifier for Frequency Standard
- R-F Sweep Oscillator
- Signal Converter
- Electronic D-C Voltmeter
CHAPTER 7 – SUPPLEMENTARY APPLICATIONS
- Frequency Divider
- Microwave Limiter
- Wave Filters
- Voltage Tuned Pi Network
- Balanced Modulator
- Ultrahigh Resistance Switch
- Capacitive Potentiometer
- Light-Controlled Capacitor
- Negative Reactor
- Varactor Effects in Conventional Diodes