Dînî Dûbêrên Gunn: Yekane û Piramîna Werkekirina We? (Tiryaş û Piramîna Werkekirina)

Gunn Diode Oscillator çi ye?

Gunn Diode Oscillator (dema Gunn oscillator an jî transferred electron device oscillator) microwave gucuêna pêşkeftinên serdemênan derbasdar in û di navbera yekan de di benda ku têrêfdekirina diodê ya Gunn an transferred electron device (TED) de were. Wan wergera Reflex Klystron Oscillators din. Di Gunn oscillators de, Gunn diode di cavitaya rezonant de nehat dabeşin. Gunn oscillator ji du komponentên major yên ve ibaret e: (i) DC bias û (ii) Tuning circuit.

Gunn Diode Oscillator ên çi vêshe?

DC Bias

Di dema diodê ya Gunn de, hêliya DC bias bigere, divê hesabê current di destpêkê de bigere, ku ji berê voltage threshold da dibêje. Pas vê, current di dema ku voltage bigere de dibêje heta voltage breakdown bibe. Ev parçeyê ku ji peak hatiye valley point, li gorî negative resistance region (Figure 1) hejmar dihet.

Ev xasîya diodê ya Gunn bi xasîya timeyên wê dikare wekheviyê oscillator bikin heta current optimal di navbera wê de be. Çunki, negative resistance property ya device wê effect ya her resistance ku di circuit de heye negirê.

Ev îmkan diha diha vêya sustained oscillations heta DC bias hene, lê dilêzîna oscillationsê. Weheraz, amplitûda resultant oscillations bi herên negative resistance region dibêje, li gorî Figure 1.

Tuning Circuit

Di dema Gunn oscillators de, frequency ya oscillation li gorî layer active middle ya diodê ya gunn depend dike. Lê resonant frequency diha diha tune bike bi mechanical an electrical means. Di tuning circuit electronic de, control bi karîne waveguide an microwave cavity an varactor diode an YIG sphere.

Lê di navbera mechanical tuning de, mezinahiya cavity an magnetic field (ji bo YIG spheres) bi rêzikê adjusting screw, tune bike.

Ev cûre oscillatoran bikaranîn bi microwave frequencies rangandîn ji 10 GHz hatiye few THz, li gorî dimensions ya resonant cavity. Coaxial û microstrip/planar based oscillator designs power factorê wan ên zêdetir û less stable di termine temperature de. Lê waveguide û dielectric resonator stabilized circuit designs power factorê wan ên zêdetir û thermal stability.

Figure 2 shows a coaxial resonator based Gunn oscillator which is used to generate the frequencies ranging from 5 to 65 GHz. Here as the applied voltage Vb is varied, the Gunn diode induced fluctuations travel along the cavity to get reflected from its other end and reach back their starting point after time t given by

Where, l is the length of the cavity and c is the speed of light. From this, the equation for the resonant frequency of the Gunn oscillator can be deduced as

where, n is the number of half-waves which can fit into the cavity for a given frequency. This n ranges from 1 to l/ctd where td is the time taken by the gunn diode to respond to the changes in the applied voltage.

Here the oscillations are initiated when the loading of the resonator is slightly higher than the maximum negative resistance of the device. Next, these oscillations grow interms of amplitude until the average negative resistance of the gunn diode becomes equal to the resistance of the resonator after which one can get sustained oscillations. Further, these kind of relaxation oscillators have a large capacitor connected across the gunn diode so as to avoid burning-out of the device due to the large amplitude signals.

Lastly, it is to be noted that the Gunn diode oscillators are extensively used as radio transmitters and receivers, velocity-detecting sensors, parametric amplifiers, radar sources, traffic monitoring sensors, motion detectors, remote vibration detectors, rotational speed tachometers, moisture content monitors, microwave transceivers (Gunnplexers) and in the case of automatic door openers, burglar alarms, police radars, wireless LANs, collision avoidance systems, anti-lock brakes, pedestrian safety systems, etc.

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