Low-power CMOS VCO with a low-current, high-Q active inductor

This study describes an active inductor (AI) designed to reduce power consumption and to improve the quality factor. For these purposes, one of the transistors for the AI operates in the subthreshold region, and the AI uses the additive capacitor (AC) technique. The proposed AI was applied to a voltage controlled oscillator (VCO) to demonstrate the enhancement in power consumption and improvement in phase noise. The AI-VCOs with and without AC were fabricated using a 0.18 μm CMOS process and achieved frequency tuning ranges from 1.13 to 2.67 GHz and 1.3 to 3.24 GHz, respectively. The measured phase noise of the AI-VCO with AC is -92.2 dBc/Hz at 1 MHz offset, a 4 dB improvement compared to that of the AI-VCO without AC. The proposed VCO consumes 2.2-13 mW with a 1.8 V voltage supply and occupies 171 × 174 μm² of core size without testing pads.