A ±0.7 ppm Analog Temperature Compensated Crystal Oscillator using an Oscillator Circuit Biased by CTAT Current

This paper presents an improved voltage controlled crystal oscillator for the ATCXO, which uses variable MOS capacitors to regulate its frequency, thus achieving higher compensation accuracy in a smaller area. The enhanced VCXO is biased using a CTAT current source, a method that eliminates the temperature variation effects on ATCXO compensation accuracy of conventional pierce oscillator circuits. Based on this, the ATCXO's temperature compensation voltage coefficient is modified to compensate for output frequency variations caused by temperature changes in the MOS capacitors own capacitance, achieving higher compensation accuracy. The design achieves frequency compensation accuracy of ±0.7ppm over the -$40^{\circ}C$ to $85^{\circ}C$ temperature range in a $0.23\times 0.26mm^{2}$ footprint using a 110 nm CMOS process.