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An electrical stimulus based built in self test (BIST) circuit for capacitive MEMS accelerometer

Description

Micro Electro Mechanical Systems (MEMS) is one of the fastest growing field in silicon industry. Low cost production is key for any company to improve their market share. MEMS testing is challenging since input to test a MEMS device require

Micro Electro Mechanical Systems (MEMS) is one of the fastest growing field in silicon industry. Low cost production is key for any company to improve their market share. MEMS testing is challenging since input to test a MEMS device require physical stimulus like acceleration, pressure etc. Also, MEMS device vary with process and requires calibration to make them reliable. This increases test cost and testing time. This challenge can be overcome by combining electrical stimulus based testing along with statistical analysis on MEMS response for electrical stimulus and also limited physical stimulus response data. This thesis proposes electrical stimulus based built in self test(BIST) which can be used to get MEMS data and later this data can be used for statistical analysis. A capacitive MEMS accelerometer is considered to test this BIST approach. This BIST circuit overhead is less and utilizes most of the standard readout circuit. This thesis discusses accelerometer response for electrical stimulus and BIST architecture. As a part of this BIST circuit, a second order sigma delta modulator has been designed. This modulator has a sampling frequency of 1MHz and bandwidth of 6KHz. SNDR of 60dB is achieved with 1Vpp differential input signal and 3.3V supply

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Date Created
2013

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Calibration of MEMS capacitive accelerometers using electrical stimulus BIST

Description

The applications which use MEMS accelerometer have been on rise and many new fields which are using the MEMS devices have been on rise. The industry is trying to reduce the cost of production of these MEMS devices. These devices

The applications which use MEMS accelerometer have been on rise and many new fields which are using the MEMS devices have been on rise. The industry is trying to reduce the cost of production of these MEMS devices. These devices are manufactured using micromachining and the interface circuitry is manufactured using CMOS and the final product is integrated on to a single chip. Amount spent on testing of the MEMS devices make up a considerable share of the total final cost of the device. In order to save the cost and time spent on testing, researchers have been trying to develop different methodologies. At present, MEMS devices are tested using mechanical stimuli to measure the device parameters and for calibration the device. This testing is necessary since the MEMS process is not a very well controlled process unlike CMOS. This is done using an ATE and the cost of using ATE (automatic testing equipment) contribute to 30-40% of the devices final cost. This thesis proposes an architecture which can use an Electrical Signal to stimulate the MEMS device and use the data from the MEMS response in approximating the calibration coefficients efficiently. As a proof of concept, we have designed a BIST (Built-in self-test) circuit for MEMS accelerometer. The BIST has an electrical stimulus generator, Capacitance-to-voltage converter, ∑ ∆ ADC. This thesis explains in detail the design of the Electrical stimulus generator. We have also designed a technique to correlate the parameters obtained from electrical stimuli to those obtained by mechanical stimuli. This method is cost effective since the additional circuitry needed to implement BIST is less since the technique utilizes most of the existing standard readout circuitry already present.

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Date Created
2014

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Design and calibration of a 12-bit current-steering DAC using data-interleaving

Description

High speed current-steering DACs with high linearity are needed in today's applications such as wired and wireless communications, instrumentation, radar, and other direct digital synthesis (DDS) applications. However, a trade-off exists between the speed and resolution of Nyquist rate

High speed current-steering DACs with high linearity are needed in today's applications such as wired and wireless communications, instrumentation, radar, and other direct digital synthesis (DDS) applications. However, a trade-off exists between the speed and resolution of Nyquist rate current-steering DACs. As the resolution increases, more transistor area is required to meet matching requirements for optimal linearity and thus, the overall speed of the DAC is limited.

In this thesis work, a 12-bit current-steering DAC was designed with current sources scaled below the required matching size to decrease the area and increase the overall speed of the DAC. By scaling the current sources, however, errors due to random mismatch between current sources will arise and additional calibration hardware is necessary to ensure 12-bit linearity. This work presents how to implement a self-calibration DAC that works to fix amplitude errors while maintaining a lower overall area. Additionally, the DAC designed in this thesis investigates the implementation feasibility of a data-interleaved architecture. Data interleaving can increase the total bandwidth of the DACs by 2 with an increase in SQNR by an additional 3 dB.

The final results show that the calibration method can effectively improve the linearity of the DAC. The DAC is able to run up to 400 MSPS frequencies with a 75 dB SFDR performance and above 87 dB SFDR performance at update rates of 200 MSPS.

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Date Created
2014

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Electrical stimulus-based characterization for calibration and testing of MEMS accelerometer and gyroscope

Description

Micro-Electro Mechanical System (MEMS) is the micro-scale technology applying on various fields. Traditional testing strategy of MEMS requires physical stimulus, which leads to high cost specified equipment. Also there are a large number of wafer-level measurements for MEMS. A method

Micro-Electro Mechanical System (MEMS) is the micro-scale technology applying on various fields. Traditional testing strategy of MEMS requires physical stimulus, which leads to high cost specified equipment. Also there are a large number of wafer-level measurements for MEMS. A method of estimation calibration coefficient only by electrical stimulus based wafer level measurements is included in the thesis. Moreover, a statistical technique is introduced that can reduce the number of wafer level measurements, meanwhile obtaining an accurate estimate of unmeasured parameters. To improve estimation accuracy, outlier analysis is the effective technique and merged in the test flow. Besides, an algorithm for optimizing test set is included, also providing numerical estimated prediction error.

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Date Created
2012