A temperature compensated VCO using feed-forward gain multiplication for cellular applications

A new LC-tank VCO to minimize frequency drift due to temperature variations for cellular applications is presented. By employing the feed-forward VCO gain multiplication technique, frequency drift is reduced by 83% without resorting to conventional temperature dependent biases and circuits. Additionally, the compensation circuit retains the original VCO behavior with no degradation in performance. A fractional-N PLL fabricated in 40 nm CMOS shows that the VCO draws 9 mA and the temperature compensation circuit draws 200 μA. Measurements show that the VCO has a tuning range of 46% (from 2890 MHz to 4560 MHz) and a phase noise of -102 dBc/Hz at 200 kHz offset centered at 3960 MHz at the PLL output before the divide-by-two circuit for 3G/LTE Band I.