A 0.4-V, 90 350-MHz PLL With an Active Loop-Filter Charge Pump

A 0.4-V phase-locked loop (PLL) that has much improved power efficiency is realized in standard 65-nm CMOS. The PLL employs a novel ultralow-voltage charge pump that compensates current mismatch with an active loop filter and produces significantly reduced reference spurs. Its voltage-controlled oscillator (VCO) is designed with the body-bias technique and includes an automatic frequency calibration circuit that provides low VCO gain and wide tuning range. The PLL output frequency can be tuned from 90 to 350 MHz. At 350-MHz output, the PLL consumes 109 μW, which corresponds to the power efficiency of 0.31 mW/GHz.