EXPERIMENT NO:5
GUNN DIODE CHARACTERISTICS
Aim:-
To study V-I characteristics of Gunn Diode
Equipment required:-
Gunn oscillator, Gun power supply, PIN modulator, Isolator, Frequency meter, Variable
attenuator, Detector mount, Wave guide stands, SWR Meter, Cables and accessories.
Theory:-
The Gunn Oscillator is based on negative differential conductivity effect in bulk
semiconductors, which has two conduction bands minima separated by an energy gap
(greater than thermal agitation energies). A disturbance at the cathode gives rise to high field
region, which travels towards the anode. When this high field domain reaches the anode, it
disappears and another domain is formed at the cathode and starts moving towards anode and
so on. The time required for domain to travel from cathode to anode (transit time) gives
oscillation frequency. In a Gunn Oscillator, the Gunn diode is placed in a resonant cavity. In
this case the Oscillation frequency is determined by cavity dimension than by diode itself.
Although Gunn oscillator can be amplitude modulated with the bias voltage. We have used
separate PIN modulator through PIN diode for square wave modulation.
BLOCK DIAGRAM:-
Procedure:-
1. Set the components and equipment as shown in the fig.
2. Set the variable attenuator for no attenuation.
3. Keep the control knob of Gunn Power Supply as given
Gunn bias knob : fully anti- clockwise(Minimum position)
Mode switch : CW Mode ..
4. Switch ON the Gunn power supply and cooling fan.
5. Measure the Gunn diode current corresponding to the various voltage controlled by Gunn
bias knob through the panel and do not exceed the bias voltage above 7 volts.
Note: Do not keep Gunn bias knob position at threshold position for more than10-15
seconds. Reading should be obtained as fast as possible. Otherwise due to excessive
heating, gunn diode may burn.
OBSERVATION:-
Sr.No. V (v) I (mA)
GRAPH:-
RESULT:-
The V-I characteristic of Gunn diode is studied and plotted.
The threshold voltage of Gunn diode = ………………V
