A varactor diode is a P-N junction diode that changes its capacitance and the series resistance as the bias applied to the diode is varied The property of capacitance change is utilized to achieve a change in the frequency or the phase of an electrical circuit Let’s we have a overview of a varactor diode, that includes working, construction, application and characteristics Varactor Diode is a one kind of semiconductor microwave solid-state device Varactor diodes are also named as Varicap diodes The outcomes of the variable capacitance can be showed by the normal P-N junction diodes

1. VIRENDRA THAKUR
SAP NO-40507190005
TOPIC- VARACTOR,STEP
RECOVERY DIODES AND
FREQUENCY MULTIPER

2. VARACTOR DIODE
A varactor diode is a P-N junction diode that changes its
capacitance and the series resistance as the bias applied to the
diode is varied The property of capacitance change is utilised to
achieve a change in the frequency or the phase of an electrical
circuit Let’s we have a overview of a varactor diode,that includes
working, construction, application and characteristics

3. What is a Varactor Diode?
• Varactor Diode is a one kind of semiconductor microwave solid-
state device
• Varactor diodes are also named as Varicap diodes
• The outcomes of the variable capacitance can be showed by the
normal P-N junction diodes
• These diode are chosen for giving the desired capacitance
changes as they are special types of diodes
• Varactor Diode are specially fabricated and optimised such that
they permits a high range of changes in capacitance

4. Symbol of Varactor Diode
• The symbol of the Varactor Diode look like a common PN
junction diode
• It inculdes two terminals namely the cathode and anode
• At one end of this diode is inbuilt with lines that specifies the
capacitor symbol

5. Materials and construction
• This Varactor Diode is
made of gallium
arsenide
• GaAs has advantage as
a higher maximum
operating frequency
and better functioning
at the lowest
temperature
• Both the advantages
are due to the higher
mobility of charge
carriers exhibited by
GaAs

6. Working of a Varactor Diode
• To know the Varactor Diode working principle
• We must know the function of capacitor and capacitance
• Lets us consider the capacitor that comprises of two plates
alienated by the insulators

7. • The capacitance of a capacitor is directly proportional to the
region of the terminals
• When the diode is in the reverse biased mode
• Where the two regions of P-type and N-type are able to conduct
and thus can be treated as two terminals
• The depletion area between the P-type and N-type regions can be
considered as insulating dielectric
• The volume of the depletion region of the diode varies with thd
changes in reverse bias
• If the reverse voltage of the diode is increased,then the size of the
depletion region increase

8. As the reverse voltage increases the capacitance is decrease,they
are inversely proportional to each other
Capacitance Ratio:This is commonly expressed in the form Cx / Cy
where x and y are two voltages towards the ends of the range over
which the capacitance change can be measured.

9. Equivalent circuit of Varactor Diode
CJ is the diode junction capacitance,C is the diode capacitance
when the device is unbiased,V is the applied voltage, Vb is the
barrier voltage at the junction,m is the constant upon the
material,K is the constant equal to 1,F is the maximum operating
frequency,f is the operating frequency

10. I-V Characteristics of Varactor Diode

11. Step Recovery Diode
• A Step Recovery Diode or snap-off Varactor is widely used in
microwave frequency multiper circuits
• A step recovery diode is a P-N junction diode made with gallium
arsenide or silicon
• When it is forward biased,it conducts like any diode,but charge is
stored in the depletion region
• When reverse bias is applied,the charge keep the diode on
momentarily and then turns off the abruptly
• This is snap off produces a high intensity pulse that is rich in
harmonics

12. Symbol of step recovery diode
• It’s also possible to use these diode without
tuned output circuit,to produce multiple
harmonic in so called Comb generators
• A comb generator is a signal generator that
produces multiple harmonics of its input signal.

13. Frequency multiper :- Practical circuits