Dainin Gunn: Me ke? (Tattalin Siyasa da Karamin Daidaita)

Mai Da Da Gunn Diode Oscillator?

Gunn Diode Oscillator (ko da ake kira Gunn oscillators ko transferred electron device oscillator) suna masu kyau a gina mikrofadi na tsohon kula da suka samu Gunn diode ko transferred electron device (TED) a matsayin muhimman yanki. Sun yi aiki mai haguwa a kan Reflex Klystron Oscillators. A cikin Gunn oscillators, za a saka Gunn diode a cikin resonance cavity. Gunn oscillator ana da biyu masu muhimmiyar yanki: (i) DC bias da (ii) tuning circuit.

Da Yaɗa Gunn Diode Yadda Yake Yi Aiki a Tsakanin Oscillator

DC Bias

A cikin Gunn diode, idan an yi karfi da applied DC bias, zai faru a lura a cikin current, wanda ya ci gaba har zuwa threshold voltage. Ba da wannan, current zai ci gaba a gama da voltage yana ci gaba har zuwa breakdown voltage. Wannan yankin da take faru daga peak zuwa valley point, ana kiran ta negative resistance region (Figure 1).

Wannan yanayin da Gunn diode ke da shi da timing properties suna bukata shi a yi aiki a tsakanin oscillator idan akwai optimum value of current ya ci gaba a cikin shi. Saboda haka, negative resistance property of the device ya fi kare dalilin any real resistance wanda ke cikin circuit.

Wannan ya ba da gina sustained oscillations har zuwa inda DC bias ya kasance a cikin shi, amma ya saukar da growth of oscillations. Duk da haka, amplitude of the resultant oscillations zai iya haɗa da limits of the negative resistance region kamar yadda aka bayyana a Figure 1.

Tuning Circuit

A cikin Gunn oscillators, frequency of oscillation ana iya ci gaba da middle active layer of the gunn diode. Amma resonant frequency zai iya tunawa waje ba tare da mechanical ko electrical means. A cikin electronic tuning circuit, control zai iya faru da amfani da waveguide ko microwave cavity ko varactor diode ko YIG sphere.

A cikin haka, diode zai saka a cikin cavity a cikin haka maimakon yadda ake fi kare loss resistance of the resonator, producing oscillations. Duk da haka, a cikin mechanical tuning, size of the cavity ko magnetic field (for YIG spheres) zai vary mechanically da amfani da, say, an adjusting screw, in order to tune the resonant frequency.

Waɗannan types of oscillators ana amfani da su don generate microwave frequencies ranging from 10 GHz to few THz, as decided by the dimensions of the resonant cavity. Usually the coaxial and microstrip/planar based oscillator designs have low power factor and are less stable in terms of temperature. On the other hand, the waveguide and the dielectric resonator stabilized circuit designs have greater power factor and can be made thermally stable, quite easily.

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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