Timing Devices (Crystal Unit / Ceramic Resonator)High-precision Crystal Units and Thermistors for Automotive UWB
Discrete Configuration and Circuit Design Support

Due to the increasing sophistication of digital keys and safety functions, high-precision timing control of broadband communications is required in automotive UWB. However, it was difficult for standalone crystal units to satisfy the required precision in high-temperature environments, and it was generally necessary to compensate with the temperature sensors built into the crystal units.
At the same time, there was a need to use crystal units and external thermistors in a discrete configuration for the purpose of cost structure optimization, but the difficulty of circuit design and temperature compensation posed a challenge. In response, Murata Manufacturing leveraged its strengths in both crystal units and thermistors to begin offering the appropriate part number recommendations and technical support for temperature characteristic compensation. As a result, our solution helps achieve the target characteristics and streamline customer design processes while providing a discrete configuration.

When using an external thermistor to compensate for the temperature characteristics of a crystal unit, the crystal unit and thermistor should be placed as close to each other as possible. Refer to here for the general placement position of NTC thermistors. In addition, contact our sales team for case studies regarding the placement of crystal units and external thermistors.

These guidelines were created based on our part numbers that were certified by IC manufacturers. However, these drawings and any related information are valid as of March 2026, and the application notes and recommendations may be subsequently changed by the IC manufacturers.
These guidelines are for reference purposes only. Appropriate evaluations and verifications must be carried out before actual use. Furthermore, the information on this site is subject to change without notice, so be sure to check the latest information before use.

The temperature characteristics of a crystal unit are generally compensated using a PLL (Phase-Locked Loop) built into the IC. In a typical design flow, the standalone temperature characteristic parameters provided by the crystal unit manufacturer are written to the IC, and that data is used to perform the compensation. However, the temperature characteristics of a crystal unit after being mounted on a board may not match the individual measurements during testing. The primary cause of this deviation is the change in load capacitance (CL) during board mounting, which impacts the frequency-temperature characteristics.
As a result, there are cases where compensation using only standard parameters may not achieve the optimal precision for the actual environment.

At Murata Manufacturing, we can measure the actual temperature characteristic parameters in the board-mounted state and provide them as data in the matching evaluation service conducted during the circuit design. This enables high-precision design using the compensation parameters optimized for the mounted board instead of the parameters from the crystal unit's standalone state. Compensation using parameters tailored to the actual mounted device is particularly effective when used in environments with significant temperature fluctuations.