5-GHz in-phase coupled oscillators with 39% tuning range

We show that when in an LC oscillator a large tuning range is required, the phase noise performance worsens. When both a wide frequency band and tight noise performance are required, a typical solution is to increase the tank capacitance, thus the power consumption. That can lead to unpractical values for the tank components. To overcome the problem, we propose a circuit realized by coupling four identical oscillators. The circuit, fabricated in an existing 0.5 /spl mu/m SiGe BiCMOS technology, achieves a 39% tuning range. Phase noise and power consumption vary respectively between -105/-95 dBc/Hz at 100 kHz offset, and 200/100 mW, with a 3 V power supply. The noise improvement due to the coupling is quantitatively analyzed and experimentally verified.