สัญญาณรบกวนเชิงวัฏภาคในวงจรออสซิลเลเตอร์ที่ใช้ทรานซิสเตอร์รอยต่อ ไบโพลาร์ / เด่นพงษ์ ณ พัทลุง = Phase noise in oscillator using a bipolar-junction transistor / Denpong Na Pattalung
Phase noise in oscillator is a factor that degrades performance of the communication systems. Decreasing the phase noise increases the channel's capacity. Phase noise can be decreased by 2 methods. One is design an oscillator that has low background noise. The other is design an oscillator that has low level of conversion of the background noise to phase noise. To find a proper way in oscillator design, this thesis studies the phase noise using large signal analysis at an approximate frequency of 73 MHz by comparing 3 types of clapp oscillator using a bipolar-junction transistor, the common base, the common collector and the common emitter circuits. The component values are varied in the range that the oscillator has low background noise. Results from the study of 3 type of oscillators show that designing an oscillator with low background noise and high value of the ratio of the imaginary part of the resonator and the imaginary part of the capacitor in the resonator can decrease phase noise in both the lowand high offset-frequency cases. However the component values of the lowest phase noise oscillators in both the low and high offset-frequency cases depend on the type of the amplifier circuits. It is found that the common base circuit is suitable for designing an oscillator with low phase noise for the high offset frequency case, because its phase noise can be suppressed as low as posible. However at low offset frequency, the phase noise has a limited value. The common emitter is the best of the three circuit topologies in decreasing phase noise for the low offset-frequency case.
