A 0.4-V 32-kHz Pulse-Injection Temperature-Compensated Crystal Oscillator With Sub-Cycle CL Modulation and DLL-Reused Temperature Sensor

This article presents a 0.4-V 32 kHz pulse-injection (PI) temperature-compensated crystal oscillator (TCXO) that incorporates subcycle capacitive load ( $C_{\text {L}}$ ) modulation for frequency compensation. The proposed TCXO compensates for the crystal’s frequency deviation ( $\Delta f$ ) by dynamically adjusting the enabling duration of the additional $C_{\text {L}}$ within each cycle, thereby ensuring long-term frequency stability. Notably, the design leverages the loop control voltage within a thyristor-based delay-locked loop (DLL) to facilitate energy injection and temperature acquisition for precise compensation. We fabricated the TCXO using the CMOS 65 nm process. Experimental results demonstrate that the TCXO achieves a frequency stability of ±8.5 ppm across a temperature range of ${-} 30~{^{\circ }}$ C to $85~{^{\circ }}$ C, while consuming 179.4 nW of power. The achieved Allan deviation (ADEV) of 15.9 parts per billion (ppb) at a 1-s gating interval highlights its superior performance in low-power and high-stability applications.