Designs of low power, low phase noise voltage-controlled oscillators

Abstract

Phase noise of voltage-controlled oscillators (VCOs) is a key figure in the design of wireless communication systems. If the phase noise is low, it will lower the bit error rate of the systems. It is well known that in VCO designs the higher the power consumption, the lower the phase noise. However, if too much power is used for the VCOs, the battery life will be shorter. Therefore, low power and low phase noise are two of the most important concerns when designing the VCOs to extend the battery life and lower the bit error rate of the wireless communication systems, respectively. In this dissertation, three low power, low phase noise VCOs are proposed. The first two VCOs aim at the target of small power consumption and very low far-out phase noise. Meanwhile, the last VCO deals with the close-in phase noise. All three proposed VCOs are designed using TSMC 0.18 μm CMOS technology. The first VCO is called the tuned-input tuned-output (TITO) VCO with loop gain enhancement. By using a negative conductance in parallel with the output tank, the minimum start-up requirement of the single-ended TITO oscillator can be as small as or even smaller than that of the cross-coupled LC oscillator. Compared to the conventional TITO VCO, the proposed TITO VCO has the loop gain which is 2.5 times higher, and saving 58% of power consumption. The measurement result of the first proposed VCO shows that the phase noise is -120.5 dBc/Hz at 1 MHz offset frequency from the oscillation frequency of 6.08 GHz while dissipating 1.5 mA from a 1.8-V supply. The VCO has an excellent FOM of -191.9 dBc/Hz. The second proposed VCO is the dual positive feedback VCO with noise cancellation. By employing two positive feedback loops to enhance its output swing and to partially cancel the drain noise currents of active devices, the proposed VCO can operate at a low supply voltage and has excellent phase noise performance in the 1/f 2 region. The measurement result of the second VCO shows that the p...