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This paper presents a 25-MHz fully-integrated digitally controlled crystal oscillator(DCXO) with automatic amplitude control(AAC).The DCXO is based on Colpitts topology for one-pin solution.The AAC circuit is introduced to optimize the phase noise performance.The automatic frequency control is realized by a 10-bit thermometer-code segmental tapered MOS capacitor array,ensuring a～35 ppm tuning range and～0.04 ppm frequency step.The measured phase noise results are-139 dBc/Hz at 1 kHz and-151 dBc/Hz at 10 kHz frequency offset,respectively.The chip consumes 1 mA at 1.8V supply and occupies 0.4 mm~2 in a 0.18-μm CMOS process.
This paper presents a 25-MHz fully-integrated digitally controlled crystal oscillator (DCXO) with automatic amplitude control (AAC). The DCXO is based on a Colpitts topology for one-pin solution. The AAC circuit is introduced to optimize the phase noise performance. The automatic frequency control is realized by a 10-bit thermometer-code segmental tapered MOS capacitor array, ensuring a ~ 35 ppm tuning range and ~ 0.04 ppm frequency step. The measured phase noise results are -139 dBc / Hz at 1 kHz and- 151 dBc / Hz at 10 kHz frequency offset, respectively. The chip consumes 1 mA at 1.8V supply and occupies 0.4 mm ~ 2 in a 0.18-μm CMOS process.