An Adaptive Methodology for Mode Switching in Crystal Oscillators: Leveraging Amplitude Detection for Negative Resistance Boosting Quick Start-Up

As the fundamental timing reference in integrated circuit systems, the clock signal is often required to have extremely short start-up time. Existing methods to improve startup time typically employ external signal control to drive the crystal, which evidently compromises the circuit’s integration and power efficiency. This paper presents a quick start-up 32.768 kHz crystal oscillator with adaptive dual-mode switching. During the start-up phase, the negative resistance boosting (NRB) technique is applied by a multistage amplifier to shorten the start-up time. Transition from boost-mode to steady-mode is controlled through amplitude detection, facilitating dual-mode adaptive operation without the reliance on external clocks. This approach enhances the robustness and integration of the circuit while effectively mitigating the increase in power consumption typically associated with NRB. As a validation, the proposed technique is incorporated into the design of a crystal oscillator and implemented in 180 nm CMOS technology, where experiments show that the start-up time and the power consumption of the core starting circuit are 116 ms and 1.03 µW, respectively.