Driver Monitoring System
Driver monitoring systems (DMS) are increasingly designed into vehicles to help offset the rise of distracted driving. Advances in driver monitoring tech and new safety regulations are accelerating this trend. These systems require low latency and high bandwidth as they monitor drivers in real time.
Clocking plays a key role in DMS as data is transferred from the camera to the SoC/processor and out to vehicle systems. SiTime MEMS timing technology delivers the reliability, robustness and stability over temperature needed. Our low-jitter differential oscillators keep clock jitter within spec, even in the toughest environments.
SiTime MEMS Timing Benefits
Complete MEMS clock treeLow jitter differential oscillators 32.768-kHz XOs and TCXOs Precision TCXOs Spread spectrum oscillators |
Most robust in real world conditions150 fs rms jitter, excellent PSNR Resistant to shock and vibration Stable over wide temperature >2 billion hours MTBF |
Integrated MEMS, easy to useNo quartz reliability issues Reliable startup in cold temp No cover or shielding needed Short lead time for any frequency |
Driver Monitoring System Block Diagram
A camera, either infrared or visible wavelength, monitors the driver's face. Data is sent to an image processing system based on an SoC and a machine-learning vision processor, which can be either internal to the SoC or external as shown here. In the latter case, data transfer between the two is usually done via a PCI-Express interface, which offers both the required low latency and high bandwidth.
The DMS is connected to other vehicle systems (Instrument cluster, drivetrain electronics, etc.) through CAN, Flexray and/or Ethernet interfaces.
MEMS Timing Solutions for Driver Monitoring System
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Single-ended Oscillator
SiT8924 1 to 110 MHz
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Single-ended Oscillator
SiT9025 1 to 110 MHz
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Differential Oscillators
SiT9396 1 to 220 MHz
SiT9397 220 to 920 MHz
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Super-TCXOs
SiT5386 1 to 60 MHz
SiT5387 60 to 220 MHz
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32.768 kHz Oscillator
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1 12 kHz to 20 MHz integration range
Driver Monitoring System
The clock requirements of the driver monitoring system shown in the block diagram above are as follows:
- PHY: either a single-ended clock for interfaces such as FPD Link (TI), GMSL (Analog Devices), or a differential clock for interfaces such as MIPI A-Phy (Valens)
- SoC, Vision Processor: single-ended clock
- PCI-Express interface: 100 MHz HCSL or LP-HCSL clock with jitter level compatible with the considered PCI-Express generation. Clock jitter outside specifications create transmission errors on the bus!
- As of 2022, PCI-Express Gen 4 is common in automotive applications. The corresponding jitter requirement is 0.5 fs RMS phase noise, integrated over 12 kHz to 20 MHz. SiTime SiT9396 oscillator meets this requirement with margin to spare.
Compared to other automotive applications, driver monitoring systems are less demanding in terms of clocking. Still, a few points remain important:
- System level functional safety and SOTIF needs to be guaranteed
- Temperature range of -40°C to +105°C or more is mandatory
- Clock jitter needs to be within spec
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, 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.
- With crystal-based oscillators, shock and vibration usually translate into increased clock jitter. This is due to mechanical coupling of vibrations into the crystal.
- Silicon MEMS oscillators are 100x more resilient to shock, vibration and electromagnetic interference than crystal-based devices, due to the smaller size (0.4 x 0.4 mm) and lower mass of MEMS resonators compared to crystal resonators. Consequently, jitter and bit error rate of data busses remain controlled even under harsh conditions. SOTIF (Safety of the Intended Functionality) is maintained regardless of the operating conditions. Physical non-reversible damage of the oscillator is also prevented.
MEMS Timing Outperforms Quartz
Higher Quality |
Higher Reliability |
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Tighter Stability |
Better EMI Reduction |
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Immune to Vibration |
Better Noise Rejection |
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Additional Resources
