Automotive LiDAR

LiDAR, together with radar and camera vision, is one of the key sensing elements of ADAS systems. Precision timing and low jitter are critical in LiDAR systems. SiTime MEMS oscillators provide frequency stability over temperature with AEC-Q100 grade 1 (-40°C to +125°C) reliability. Our differential oscillators provide ultra-low jitter, enabling the reliable and rapid transfer of data. Compared to quartz oscillators, SiTime timing solutions offer higher reliability, better resilience to shock, vibration and EMI, and faster startup.

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LiDAR Block Diagram

LiDAR (light detection and ranging) determines range by targeting an object with laser and measuring the time for the reflected light to return to the receiver. LiDAR systems scan the vision field vertically and horizontally, some can scan 360°, hence creating a 3D representation of the environment around a vehicle.

At the core of a LiDAR system are a solid-state laser source, a detector and the analog front end (AFE). An ADC samples the signal received by the AFE. After processing, the data collected by the LiDAR system is sent to a domain controller or ADAS computer via a PHY. Many different interfaces exist, for instance Ethernet, FPD-Link (TI) or GMSL (Analog Devices). Open standards such as Automotive Serdes Alliance (ASA) or MIPI A-PHY are emerging. Depending on the interface, either a single ended or a differential clock will be needed.

Automotive LiDAR

Several measurement methods exist: Time of flight (ToF), frequency modulated continuous wave, or time digital conversion (TDC). Precision timing plays a big role to ensure accuracy of the system. The low jitter of the SiT9396 and SiT9397 make those devices ideal to clock the analog part of LiDAR applications.

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When an ADC is used, jitter causes quantization errors. When excessive jitter is present on a clock, in other words when a clock edge comes too early or too late, an ADC samples the incoming signal at the wrong moment. Incorrect values in the data stream can significantly hamper the functionality of a system.

The excellent dynamic performance of SiTime silicon MEMS oscillators facilitate SOTIF (safety of the intended functionality) compliance of the system. The MEMS oscillators ensure that clocks remain within spec over its entire lifetime, regardless of environmental changes.

• Temperature range -40°C to +125°C
• Well controlled frequency stability: < ±30 ppm over the full temperature range, including 10 years aging (SiT939x), down to ±0.1 ppm for TCXO (SiT538x)
• Excellent frequency response to rapid temperature changes dF /dT, down to < ±3.5 ppb/°C (SiT538x)

SiTime Advantages

All SiTime devices offer the following advantages over quartz crystals, which are particularly important for automotive applications:

• 50x better reliability. Apart from reducing the amount of field failures, the better reliability translates into a lower FIT rate. This provides better hardware safety metrics in an FMEDA, the quantitative analysis required as part of a functional safety assessment.
• 100x better resilience to shock, vibration and electromagnetic interference, due to the smaller size (0.4 x 0.4 mm) and lower mass of MEMS resonators compared to crystals.
• MEMS oscillators typically have a faster startup time than crystal oscillators.

Additional Resources

• Timing Solutions for Automotive Systems
• ADAS Computer
• Automotive Cameras
• Increase automotive reliability and performance with ultra-robust MEMS oscillators
• AEC-Q100 Automotive Oscillators for ADAS Sensors, in-Vehicle Networking & Self-Driving Computer
• EMI Reduction Oscillators for Industrial, Automotive and Consumer Applications