Low voltage, low phase noise and wide tuning range integrated oscillator design

The requirement of phase noise in integrated oscillators has been driven by wireless applications, especially the base station. As device scaling continues, the device breakdown voltage will be reduced, so the low voltage supply VCO is needed, and the Q factor of the passive element (inductor) will not improve. Therefore, improvement in simple LC oscillator phase noise will be limited since the carrier/phase noise ratio of the oscillator is proportional to the voltage swing. A smaller inductor, which has a smaller equivalent parallel resistance (Rp), can be used to draw more current but keep the voltage swing below breakdown voltage. Although more power in the tank can increase the carrier, the smaller Q will degrade the FOM. The traditional simple LC structure offers limited improvement of phase noise, supply voltage and tuning range. In this research, two new architectures are proposed.; An on-chip tapped inductor technique is shown to be one of the efficient methods for reducing oscillator phase noise. Higher signal amplitude can be achieved while avoiding breakdown and without penalty in area, tuning range, FOM and supply voltage. Two commercial SiGe BJT and InGaP-GaAs HBT processes were used to fabricate a 2.4GHz and 1GHz VCO respectively.; Phase noise can also be reduced with the same resonator voltage swing by coupling several (N) identical oscillators to each other, and the phase noise will be reduced by a factor of 1/N. But the chip area will be increased in the same proportion. A transformer based area-saving coupled oscillator was evaluated. Several individual oscillators were combined by a transformer. This technique no only can reduce the phase noise, but also provide more flexibility on trading off between phase noise, FOM, tuning range, area and supply voltage. The transformer power combining technique has been used to design a 5GHz VCO and 1GHz VCO using a 0.18um CMOS process and InGaP-GaAs HBT process respectively.