First MEMS clock generator SoC for automotive
SiTime has launched the industry’s first fully integrated clock system-on-a-chip (ClkSoC) with built-in fault monitoring mechanisms for the entire clock generation signal path for automotive designs.
The Chorus Automotive Clock Generator (see below) developed by SiTime uses a micromachined MEMS resonator, oscillator and advanced safety mechanisms into a single package. This integration, which SiTIme calls FailSafe, simplifies system timing architecture for multiple clock trees and accelerates functional safety development time by up to six weeks. Hardware designers get the combined benefits of up to 10X higher performance in half the size compared to standalone quartz oscillators and also provides critical diagnostic coverage to achieve functional safety metrics more easily.
The clock generator is aimed at autonomous driving (AD) or advanced driver assistance system (ADAS) for safety-critical electronics, building on devices used in the data centre, says Sumeet Kulkarni, Director of Product Marketing, Automotive at SiTime.
Using the ruggedized MEMS timing technology and synchronized high precision timing networks for datacentres to the automotive industry allows operation from -40°C to 125°C to remove any thermal bottlenecks in the design and positioning of safety critical modules.
Conventionally, if the clock for a critical component fails, catastrophic failures can occur – a processing unit may stop operating, or a high-speed link may drop packets. A safety microcontroller in the system monitors such large-scale failures and disables the failing function to reach a safe state.
Engineers aim to reduce this fault-tolerant time interval (FTTI, or the time between a fault occurring and the system notification). Chorus automotive can shave off critical milliseconds by reporting clock failures far earlier.
FTTI requirements are common for Automotive Safety Integrity Level (ASIL), part of the ISO 26262 standard, the framework for classifying hazards caused by malfunctioning automotive systems. ADAS sensors and central compute ECUs are expected to meet the requirements of high ASIL ratings to be certified for managing the most critical hazards despite malfunctions. Each module requires a detailed analysis of failure scenarios, assigning failure probabilities and diagnostic coverage metrics to every component part.
In the past, the timing network consisted of standalone oscillators. These oscillators could not be synchronized, nor did they have diagnostic features. Sometimes multi-output clock generators were used, commonly paired with an external quartz resonator, which suffers from impedance matching and noise issues. Chorus automotive replaces up to four differential or eight single-ended standalone oscillators, shrinking the timing footprint on circuit boards by up to 50% and eliminating any noise or impedance mismatch issues.
Each Chorus clock output is individually programmable and controllable. The behaviour can be tuned for specific system needs, controlling electromagnetic interference (EMI) or adjusting phase shifts and delays to manage long circuit board traces. Now, multiple clocks can be integrated into a single compact device, for example, to consolidate a complex clock tree of an ADAS ECU or zonal gateway.
This allows a single clkSoC to handle the timing for ADAS compute SOCs and multiple high-speed interfaces, reducing the power consumption, total cost of ownership and board space.
The clkSoC has a programmable frequency from 1 MHz to 700 MHz and RMS phase jitter of 70 fs typical (12 kHz to 20 MHz). The frequency stability is ±20 ppm (-40°C to 105°C) or ±50 ppm (-40°C to 125°C) and there are up to four differential (LVPECL, FlexSwing, LVDS, HCSL, LPHCSL) or eight LVCMOS outputs. The FlexSwing output reduces power consumption and eliminates termination resistors.
The capability to alert a safety microcontroller of a clock-related fault within microseconds instead of milliseconds, far before any downstream failures can occur, means the vehicle electronics can return to a safe state up to 1000x faster than before. This combination of significantly lower failure rates, expanded diagnostics, and faster reporting allows engineers more room in their overall safety budget.
Notably, the safety microcontroller itself should be clocked by a separate oscillator to avoid any potential dependent failures. SiTime has the required expertise to advise on intelligent partitioning of the clock tree to achieve the twin goals of integration and safety.
The Chorus automotive clock generator orchestrates complex timing for automotive compute and sensor systems by providing up to four configurable differential or up to eight single-ended low skew outputs. Its FailSafe technology enables ease of functional safety design by providing programmable end-to-end safety monitors. It is PCI Express (PCIe) Generations 1 – 6 compliant, with spread-spectrum options, on-chip regulators for extremely good power supply noise rejection, and phase-configurable and programmable skew outputs.
Chorus can alert an external safety manager MCU to any clock faults via configurable general-purpose I/O (GPIO) pins. The serial interface (I2C or SPI) can be used to read internal registers, including the status of the internal monitoring functions. These devices additionally enable high levels of flexibility using the in-system configuration (ISC) mode to modify the device configuration and each output behavior via the serial interface.
The SiTime Chorus Automotive clock generator is currently sampling in a 4 mm x 4 mm QFN package.
www.sitime.com/chorus-automotive
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