A Temperature-Compensated Crystal Oscillator With Piecewise Polynomial Varactor Compensation Achieving ±3.75-ppm Inaccuracy From −30°C to 90°C

This brief presents a low-complexity temperature-compensated crystal oscillator (TCXO). The frequency error compensation over temperature is realized by employing the proposed piecewise polynomial varactor (PPV). The PPV operation is determined by a temperature-dependent voltage generator. The temperature compensation is achieved without using an accurate mapping table and high-resolution data converters. In addition, an amplitude-control loop (ACL) is incorporated to maintain a stable XO operation under process, temperature, and supply voltage variations. This brief is fabricated in a 180-nm CMOS process. The frequency inaccuracy of the proposed 40-MHz TCXO is ±3.75 ppm from −30°C to 90 °C. Operating from a 1.8-V supply, the overall current consumption, including the proposed compensation and ACL, is 0.3 mA.