X-band Low Phase Noise Vco Developed

This subject talked about the design of the X band VCOs (voltage controlled oscillators), and we will go through the theory of the oscillating condition and the realization of the low phase noise VCOs.Current X band (8-12GHz) oscillators are designed around bipolar discrete silicon transistors. These transistors have currently become obsolete. New suppliers or new designs are needed to continue production of X band oscillators. Alternatively, GaAs FET devices are suitable for microwave and millimeter wave oscillator designs but inferior phase noise performance compared to silicon germanium (SiGe) transistor, which was just made available in recent years, can be used. Conventional silicon transistors can handle frequencies from 10-20GHz, while the SiGe transistor can handle up to 50GHz.First we deduced the oscillating condition of the oscillator. Since the oscillating condition in our textbook are too complex to understand and relatively difficult to apply to the computer simulation. We find a clear and simple way from the deducing process to handle it. Then we discussed the method of low phase noise and specific realization. Next we focused on the problem that if the tuning band of the VCO are wide then the phase noise will turn bad cause the Q factor of the resonator becomes lower. A compromise must be made, so we choose the diode specifically manufactured for VCOs, called"turn diode", to realize a relative wide tuning range and a good phase noise performance.The finished VCO has good electrical character and after the debugging of the circuit we have a much better phase noise. The phase noise is–97.5dBc/Hz@100KHz from the carrier frequency 7.8GHz, and–120dBc/Hz@1MHz from the carrier frequency. We believe that after the following research the performance of this kind of VCOs must be even better.