Crystal-Less Clock Generation and Calibration for Passive BLE Tag Chips in IoT Applications

This letter presents an innovative on-chip clock generation and calibration scheme for passive Bluetooth low-energy (BLE) tag chips. While crystal oscillators are suitable for traditional active BLE systems, their high power consumption and limited integration hinder the development of passive BLE systems. We utilize a low-power, low-temperature-drift relaxation oscillator to generate a low-frequency reference signal, which is then multiplied by a charge-pumped phase-locked loop (CPPLL) to produce the required clock signal. To address clock deviations due to nonideal effects, such as process variations and the 1000-ppm baseband data rate tolerance necessary for compatibility with commercial BLE protocols, we designed a calibration circuit that supports multiple calibration processes to enhance clock accuracy. Implemented using TSMC’s 0.18-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m process technology, the circuit achieves a power consumption of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.58~\mu $</tex-math> </inline-formula>W, an energy efficiency ratio of 0.79 nW/kHz, and a compact area of just 0.0875 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The final testing results align with expectations, confirming that the tag can effectively communicate with commercial smart receiver devices.