Design scheme of low-g accelerometer for automotive inertial sensor developers
In order to shorten the development cycle of MEMS inertial sensors for commercial applications, we can reuse technologies developed for similar automotive products. The additional advantage offered by this method is that it allows commercial products to maintain the same high level of quality as automotive products. Therefore, commercial low-g accelerometers have been derived from the automotive field, and its benefits are shorter design cycles and higher product quality, while achieving lower costs.
In particular, the inertial sensor developed using the two-chip (sensor and signal conditioning chip) method makes it easy to reuse existing technology. For example, IC technology developed for other products such as analog devices or microcontrollers can be multiplexed into signal conditioning ICs. Another advantage of the two-chip approach is that it can achieve a shorter product design cycle, because the sensor and IC design can be performed at the same time, thereby reducing wafer processing time.
The automotive and commercial inertial sensor markets overlap within a certain acceleration sensing range, usually in the low-g field of less than 8 g, but automotive accelerometers require from 1 g (used for tilting) to 250 g or Higher (for collision detection, etc.) sensing range. In short, commercial applications involve a more moderate acceleration environment that the human body usually experiences, rather than shock waves caused by metal collisions.
In addition, the commercial OEM market is more diverse and decentralized than the professional automotive market. Recently, more and more consumer products, including mobile phones, portable hard drives, video game consoles, car navigation systems, and digital cameras, have begun to use inertial sensors to detect tilt, motion, shock, vibration, and placement. With many mobile phones currently equipped with games, cameras, GPS, pedometers, and anti-theft functions that rely on inertial sensors, consumer applications are becoming a huge market for inertial sensors.
In the commercial market, low prices are the primary consideration for customers when choosing suppliers, and sometimes they will try to bargain until they reach their target price. Therefore, reducing the cost of consumer sensor products is very critical for products to enter the market. The traditional method of reducing costs is to reduce die size and test time, improve yield, use low-cost packaging, mass production, and reduce development time and cost.
The difference between the automotive and commercial sensor markets is also reflected in how they evaluate the relative importance of performance, reliability, and cost in low-g applications. Automotive applications critical to safety require the highest level of quality and reliability. The most important factors for the commercial market are cost, time to market and low power consumption.
In order to prove acceptable quality and reliability levels, automotive inertial sensors must at least pass the qualification certification stipulated by the Automotive Engineering Association. In addition, these components often need to undergo additional and more stringent customer qualification tests.
By analyzing customer reports on each failed component, quality and reliability processes can be further strengthened. The automotive market requires detailed inspection of all failures, including thorough failure analysis and regular monitoring of customer failure rates, which can provide a realistic guarantee for the zero-defect plan. The one-millionth failure rate is still the key consideration.
This entire quality and reliability assurance system is expensive. In some respects, automotive-grade accelerometers are comparable to military Class B products. But unlike the military market, car users still require low prices and fast delivery times, and these items are listed as part of their requirements, although their priority is lower.
Since consumer inertial sensor products are not required to have the same high performance as automotive sensors, their circuits can be simplified, which helps reduce die size and test time and improve yield. Not only does packaging require low cost (eg, plastic packaging), it must also be small and thin in order to be used in handheld devices. In addition, mass production helps reduce the unit cost of products.
The commercial market has an endless pursuit of low cost and short product cycles, which can be satisfied by the following methods. Commercial devices derived from the automotive platform have the highest quality and reliability as the original products. The original product has amortized its deposition costs (that is, the previously incurred investment and expenditure costs). In addition, by reusing or reducing automotive platform components, building blocks and packaging, we can also shorten the time to market of commercial products and reduce their power consumption.
The three biggest factors that affect the cost of developing and producing inertial sensors are: identification, testing, and burn-in. According to the practice in the commercial market, aging can be removed from the production process. By judiciously selecting test parameters at certain stages can further reduce costs. The parameters of other stages can be guaranteed by design.
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