GUNN diode- Basic Principle
The Gunn diode is a very useful source because it is simple, rugged, and compact. Now we will study the characteristics of a Gunn diode oscillator in given below.
- Gunn diodes are used as transferred electron oscillators (TEO) by using the negative resistance property of bulk Gallium Arsenide.
- The figure below shows the electron velocity in GaAs as a function of the applied electric field.
- Greater than about an electric field of 3.2 KV/cm, the electrons in N type GaAs move from a high-mobility, lowenergy valley to another valley where the mobility is lower. Consequently, the net electron velocity is lower.
- This negative resistance is used for generation o fmicrowave power.
Tuning Of GUNN diode:
- Mechanical-frequency tuning is accomplished by inserting a tuning rod (preferably made from a low-loss dielectric such as sapphire with a dielectric constant K of 9) into the cavity.
- The tuning rate is proportional to the rod diameter; however, too large a diameter may cause waveguide modes.
- The cut-off wavelength for a rod of diameter (D), is given by:
λco = 1.7 * D * √K
- Electronic tuning is accomplished either by using a YIG sphere or by using a varactor in the oscillator.
- In the case of electronic tuning by varactors, the tuning bandwidth and the efficiency of the oscillator depend on the junction capacitance of the chip, the package capacitance (if any) and the Q of the diode (see MV 2000 and MV 3000 varactor series for selection).