MEMS Capacitive Accelerometers

Condition-based monitoring (CbM) is one form of predictive maintenance that uses sensors to assess status of equipment overtime while the equipment is operating. The collected sensor data can establish baseline trends, such as, diagnose or even predict failure. Utilizing CbM, maintenance is performed when needed as opposed to the conventional periodic preventive maintenance model, saving both time and money.

Vibration monitoring is a common type of CbM measurement because changes in vibration trends are potentially indicative of wear or other failure modes. To measure vibration data, high bandwidth (10 kHz and more), ultralow noise (100 µg/√Hz or lower) piezoelectric sensors were historically used to satisfy these requirements. The established sensor interface for piezo sensors is integrated electronics piezoelectric (IEPE), as a result, IEPE has become a de facto interface in CbM vibration ecosystem.

With recent advancements in the microtechnology processes and fabrication techniques, MEMS accelerometers have caught up with piezoelectric sensors low noise levels and supersede in other many specifications, such as dc to low frequency response, thermal stability, shock resistance and recovery, and cost. The output of MEMS sensors, however, are either conventional 3-wire analog (ground, power, and signal) or digital if integrated with an ADC. Neither output are directly compatible with IEPE, the preferred CbM industry sensor interface.

This reference design enables a direct piezoelectric sensor IEPE replacement with benefits of high bandwidth, ultralow noise MEMS accelerometers. This circuit allows customers to easily evaluate a MEMS accelerometer for CbM applications.

The ADXL1001/ADXL1002 deliver ultralow noise density over an extended frequency range with two full-scale range options, and are optimized for industrial condition monitoring. The ADXL1001 (±100 g) and the ADXL1002 (±50 g) have typical noise densities of 30 μg/√Hz and 25 μg/√Hz, respectively. Both accelerometer devices have stable and repeatable sensitivity, which is immune to external shocks up to 10,000 g.

The ADXL1001/ADXL1002 have an integrated full electrostatic self test (ST) function and an overrange (OR) indicator that allow advanced system level features and are useful for embedded applications. With low power and single-supply operation of 3.3 V to 5.25 V, the ADXL1001/ADXL1002 also enable wireless sensing product design. The ADXL1001/ ADXL1002 are available in a 5 mm × 5 mm × 1.80 mm LFCSP package, and are rated for operation over a −40°C to +125°C temperature range.

Applications

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring sytems (HUMS)

The ADXL1001/ADXL1002 deliver ultralow noise density over an extended frequency range with two full-scale range options, and are optimized for industrial condition monitoring. The ADXL1001 (±100 g) and the ADXL1002 (±50 g) have typical noise densities of 30 μg/√Hz and 25 μg/√Hz, respectively. Both accelerometer devices have stable and repeatable sensitivity, which is immune to external shocks up to 10,000 g.

The ADXL1001/ADXL1002 have an integrated full electrostatic self test (ST) function and an overrange (OR) indicator that allow advanced system level features and are useful for embedded applications. With low power and single-supply operation of 3.3 V to 5.25 V, the ADXL1001/ADXL1002 also enable wireless sensing product design. The ADXL1001/ ADXL1002 are available in a 5 mm × 5 mm × 1.80 mm LFCSP package, and are rated for operation over a −40°C to +125°C temperature range.

Applications

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring system (HUMS)

The ADXL1003 delivers ultralow noise density over an extended frequency range and is optimized for bearing fault detection and diagnostics. The ADXL1003 has typical noise density of 45 μg/√Hz across the linear frequency range. Microelectronicmechanical systems (MEMS) accelerometers have stable and repeatable sensitivity, and are immune to external shocks up to 10,000 g.

The integrated signal conditioning electronics enable such features as full electrostatic self test (ST) and an overrange (OR) indicator, useful for embedded applications. With low power and single-supply operation of 3.0 V to 5.25 V, the ADXL1003 also enables wireless sensing product design. The ADXL1003 is available in a 5 mm × 5 mm × 1.8 mm LFCSP package, and operates over the −40°C to +125°C temperature range.

APPLICATIONS

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring system (HUMSs)
• Acoustic emissions

The ADXL1004 delivers ultralow noise density over an extended frequency range and is optimized for bearing fault detection and diagnostics. The ADXL1004 has typical noise density of 125 μg/√Hz across the linear frequency range. Microelectronicmechanical systems (MEMS) accelerometers have stable and repeatable sensitivity, and are immune to external shocks up to 10,000 g.

The integrated signal conditioning electronics enable such features as full electrostatic self test (ST) and an overrange (OR) indicator, useful for embedded applications. With low power and single-supply operation of 3.3 V to 5.25 V, the ADXL1004 also enables wireless sensing product design. The ADXL1004 is available in a 5 mm × 5 mm × 1.80 mm LFCSP package, and operates over the −40°C to +125°C temperature range.

Applications

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring system (HUMSs)
• Acoustic emissions

The ADXL1005 delivers ultralow noise density over an extended frequency range and is optimized for bearing fault detection and diagnostics. The ADXL1005 has typical noise density of 75 μg/√Hz across the linear frequency range. Microelectronicmechanical systems (MEMS) accelerometers have stable and repeatable sensitivity, and are immune to external shocks up to 10,000 g.

The integrated signal conditioning electronics enable such features as full electrostatic self test (ST) and an overrange (OR) indicator, useful for embedded applications. With low power and single-supply operation of 3.3 V to 5.25 V, the ADXL1005 also enables wireless sensing product design. The ADXL1005 is available in a 5 mm × 5 mm × 1.80 mm LFCSP package, and operates over the −40°C to +125°C temperature range.

APPLICATIONS

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring system (HUMSs)
• Acoustic emissions

The analog output ADXL354 and the digital output ADXL355 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL354B supports the ±2 g and ±4 g ranges, the ADXL354C supports the ±2 g and ±8 g ranges, and the ADXL355 supports the ±2 g, ±4 g, and ±8 g ranges. The ADXL354/ADXL355 offer industry leading noise, minimal offset drift over temperature, and long-term stability enabling precision applications with minimal calibration.

Highly integrated in a compact form factor, the low power ADXL355 is ideal in an Internet of Things (IoT) sensor node and other wireless product designs.

The ADXL355 multifunction pin names may be referenced by their relevant function only for either the serial peripheral interface (SPI) or I²C interface.

Applications

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRS)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition Monitoring

The analog output ADXL354 and the digital output ADXL355 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL354B supports the ±2 g and ±4 g ranges, the ADXL354C supports the ±2 g and ±8 g ranges, and the ADXL355 supports the ±2 g, ±4 g, and ±8 g ranges. The ADXL354/ADXL355 offer industry leading noise, minimal offset drift over temperature, and long-term stability enabling precision applications with minimal calibration.

Highly integrated in a compact form factor, the low power ADXL355 is ideal in an Internet of Things (IoT) sensor node and other wireless product designs.

The ADXL355 multifunction pin names may be referenced by their relevant function only for either the serial peripheral interface (SPI) or I²C interface.

Applications

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRS)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition Monitoring

The analog output ADXL356 and the digital output ADXL357 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL356B supports the ±10 g and ±20 g ranges, the ADXL356C supports the ±10 g and ±40 g ranges, and the ADXL357 supports the ±10 g, ±20 g, and ±40 g ranges.

The ADXL356/ADXL357 offer industry leading noise, minimal offset drift over temperature, and long-term stability, enabling precision applications with minimal calibration.

The low drift, low noise, and low power ADXL357 enables accurate tilt measurement in an environment with high vibration. The low noise of the ADXL356 over higher frequencies is ideal for condition-based monitoring and other vibration sensing applications.

The ADXL357 multifunction pin names may be referenced only by their relevant function for either the serial peripheral interface (SPI) or limited I²C interface.

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRSs)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition monitoring

The analog output ADXL356 and the digital output ADXL357 are low noise density, low 0 g offset drift, low power, 3-axis accelerometers with selectable measurement ranges. The ADXL356B supports the ±10 g and ±20 g ranges, the ADXL356C supports the ±10 g and ±40 g ranges, and the ADXL357 supports the ±10 g, ±20 g, and ±40 g ranges.

The ADXL356/ADXL357 offer industry leading noise, minimal offset drift over temperature, and long-term stability, enabling precision applications with minimal calibration.

The low drift, low noise, and low power ADXL357 enables accurate tilt measurement in an environment with high vibration. The low noise of the ADXL356 over higher frequencies is ideal for condition-based monitoring and other vibration sensing applications.

The ADXL357 multifunction pin names may be referenced only by their relevant function for either the serial peripheral interface (SPI) or limited I²C interface.

• Inertial measurement units (IMUs)/altitude and heading reference systems (AHRSs)
• Platform stabilization systems
• Structural health monitoring
• Seismic imaging
• Tilt sensing
• Robotics
• Condition monitoring

The AD4000/AD4004/AD4008 are high accuracy, high speed, low power, 16-bit, precision successive approximation register (SAR) analog-to-digital converters (ADCs). These ADCs incorporate Easy Drive features, such as high-Z mode and an extended acquisition phase, which provide signal chain architectural flexibility by expanding the range of companion circuitry that can be paired with these ADCs.

Operating from a single power supply, VDD, these ADCs allow the reference voltage, V_REF, to be applied externally and set independently of the supply voltage. With fast device throughput up to 2 MSPS, the AD4000/AD4004/AD4008 can accurately capture high-frequency signals and implement oversampling techniques to alleviate the challenges associated with antialias filter designs. Additionally, the power consumption of these ADCs scales linearly with throughput.

The AD4000/AD4004/AD4008 eliminate the need for a negative supply to the ADC driver amplifier by employing input span compression, while preserving access to the full ADC code range. Furthermore, the input overvoltage clamp protects the ADC inputs against overvoltage events, minimizing disturbances on the reference pin and eliminating the need for external protection diodes.

By reducing the serial peripheral interface (SPI) clock rate requirements, the AD4000/AD4004/AD4008 reduce digital input and output power consumption, broaden digital host options, and simplify the task of sending data across digital isolation. The SPI-compatible serial user interface supports 1.8 V, 2.5 V, 3.3 V, and 5 V logic by using the separate VIO logic supply.

APPLICATIONS

• Automated test equipment
• Machine automation
• Medical equipment
• Battery-powered equipment
• Precision data acquisition systems
• Instrumentation and control systems

The ADAQ7980/ADAQ7988 are 16-bit analog-to-digital converter (ADC) μModule^® data acquisition systems that integrate four common signal processing and conditioning blocks into a system in package (SiP) design that supports a variety of applications. These devices contain the most critical passive components, eliminating many of the design challenges associated with traditional signal chains that use successive approximation register (SAR) ADCs. These passive components are crucial to achieving the specified device performance.

The ADAQ7980/ADAQ7988 contain a high accuracy, low power, 16-bit SAR ADC, a low power, high bandwidth, high input impedance ADC driver, a low power, stable reference buffer, and an efficient power management block. Housed within a tiny, 5 mm × 4 mm LGA package, these products simplify the design process for data acquisition systems. The level of system integration of the ADAQ7980/ADAQ7988 solves many design challenges, while the devices still provide the flexibility of a configurable ADC driver feedback loop to allow gain and/or common-mode adjustments. A set of four device supplies provides optimal system performance; however, single-supply operation is possible with minimal impact on device operating specifications.

The ADAQ7980/ADAQ7988 integrate within a compact, integrated circuit (IC)-like form factor key components commonly used in data acquisition signal chain designs. The μModule family transfers the design burden of component selection, optimization, and layout from designer to device, shortening overall design time, system troubleshooting, and ultimately improving time to market.

The serial peripheral interface (SPI)-compatible serial interface features the ability to daisy-chain multiple devices on a single, 3-wire bus and provides an optional busy indicator. The user interface is compatible with 1.8 V, 2.5 V, 3 V, or 5 V logic.

Specified operation of these devices is from −55°C to +125°C.

APPLICATIONS

• Automated test equipment (ATE)
• Battery powered instrumentation
• Communications
• Data acquisition
• Process control
• Medical instruments

The AD7768/AD7768-4 are 8-channel and 4-channel 24-bit, simultaneous sampling, sigma-delta (Σ-Δ) analog-to-digital converters (ADCs) with power scaling and 110.8 kHz bandwidth. The devices have a Σ-Δ modulator and digital filter per channel, which enables synchronized sampling of ac and dc signals.

The AD7768/AD7768-4 achieve 108 dB dynamic range at a maximum input bandwidth of 110.8 kHz, combined with typical performance of ±2 ppm integral nonlinearity (INL), ±50 μV offset error, and ±30 ppm gain error.

The AD7768/AD7768-4 user can trade off input bandwidth, output data rate, and power dissipation, and select one of three power modes to optimize for noise targets and power consumption. The flexibility of the AD7768/AD7768-4 allows them to become reusable platforms for low power dc and high performance ac measurement modules.

The AD7768/AD7768-4 have three modes: fast mode (256 kSPS maximum, 110.8 kHz input bandwidth, 51.5 mW per channel), median mode (128 kSPS maximum, 55.4 kHz input bandwidth, 27.5 mW per channel) and low power mode (32 kSPS maximum, 13.8 kHz input bandwidth, 9.375 mW per channel).

The AD7768/AD7768-4 offer extensive digital filtering capabilities, such as a wideband, low ±0.005 dB pass-band ripple, antialiasing low-pass filter with sharp roll-off, and 105 dB attenuation at the Nyquist frequency.

Frequency domain measurements can use the wideband linear phase filter. This filter has a flat pass band (±0.005 dB ripple) from dc to 102.4 kHz at 256 kSPS, from dc to 51.2 kHz at 128 kSPS, or from dc to 12.8 kHz at 32 kSPS.

The AD7768/AD7768-4 also offer sinc response via a sinc5 filter, a low latency path for low bandwidth, and low noise measurements. The wideband and sinc5 filters can be selected and run on a per channel basis.

Within these filter options, the user can improve the dynamic range by selecting from decimation rates of ×32, ×64, ×128, ×256, ×512, and ×1024. The ability to vary the decimation filtering optimizes noise performance to the required input bandwidth.

Embedded analog functionality on each ADC channel makes design easier, such as a precharge buffer on each analog input that reduces analog input current and a precharge reference buffer per channel reduces input current and glitches on the reference input terminals.

The device operates with a 5 V AVDD1A and AVDD1B supply, a 2.25 V to 5.0 V AVDD2A and AVDD2B supply, and a 2.5 V to 3.3 V or 1.8 V IOVDD supply (see the 1.8 V IOVDD Operation section for specific requirements for operating at 1.8 V IOVDD).

The device requires an external reference; the absolute input reference voltage range is 1 V to AVDD1 − AVSS.

The specified operating temperature range is −40°C to +105°C. The device is housed in a 10 mm × 10 mm, 64-lead low profile quad flat package (LQFP) with a 12 mm × 12 mm printed circuit board (PCB) footprint.

APPLICATIONS

• Data acquisition systems: USB/PXI/Ethernet
• Instrumentation and industrial control loops
• Audio test and measurement
• Vibration and asset condition monitoring
• 3-phase power quality analysis
• Sonar
• High precision medical electroencephalogram (EEG)/electromyography (EMG)/electrocardiogram (ECG)

The AD7768-1 is a low power, high performance, Σ-Δ analog-to-digital converter (ADC), with a Σ-Δ modulator and digital filter for precision conversion of both ac and dc signals. The AD7768-1 is a single-channel version of the AD7768, an 8-channel, simultaneously sampling, Σ-Δ ADC. The AD7768-1 provides a single configurable and reusable data acquisition (DAQ) footprint, which establishes a new industry standard in combined ac and dc performance and enables instrumentation and industrial system designers to design across multiple measurement variants for both isolated and nonisolated applications.

The AD7768-1 achieves a 108.5 dB dynamic range when using the low ripple, finite impulse response (FIR) digital filter at 256 kSPS, giving 110.8 kHz input bandwidth, combined with ±1.1 ppm integral nonlinearity (INL), ±30 µV offset error, and ±30 ppm gain error.

A wider bandwidth, up to 500 kHz Nyquist (filter −3 dB point of 204 kHz), is available using the sinc5 filter, enabling a view of signals over an extended range.

The AD7768-1 offers the user the flexibility to configure and optimize for input bandwidth vs. output data rate (ODR) and vs. power dissipation. The flexibility of the AD7768-1 allows dynamic analysis of a changing input signal, making the device particularly useful in general-purpose DAQ systems. The selection of one of three available power modes allows the designer to achieve required noise targets while minimizing power consumption. The design of the AD7768-1 is unique in that it becomes a reusable and flexible platform for low power dc and high performance ac measurement modules.

The AD7768-1 achieves the optimum balance of dc and ac performance with excellent power efficiency. The following three operating modes allow the user to trade off the input bandwidth vs. power budgets:

• Fast mode offers both a sinc filter with up to 256 kSPS and 52.2 kHz of bandwidth, and 26.4 mW of power consumption, or a FIR filter with up to 256 kSPS, 110.8 kHz of bandwidth and 36.8 mW of power consumption.
• Median mode offers a FIR filter with up to 128 kSPS, 55.4 kHz of bandwidth and 19.7 mW of power consumption.
• Low power mode offers a FIR filter with up to 32 kSPS, 13.85 kHz of bandwidth and 6.75 mW of power consumption.

The AD7768-1 offers extensive digital filtering capabilities that meet a wide range of system requirements. The filter options allow configuration for frequency domain measurements with tight gain error over frequency, linear phase response requirements (brick wall filter), a low latency path (sinc5 or sinc3) for use in control loop applications, and measuring dc inputs with the ability to configure the sinc3 filter to reject the line frequency of either 50 Hz or 60 Hz. All filters offer programmable decimation.

A 1.024 MHz sinc5 filter path exists for users seeking an even higher ODR than is achievable using the low ripple FIR filter. This path is quantization noise limited. Therefore, it is best suited for customers requiring minimum latency for control loops or implementing custom digital filtering on an external field programmable gate array (FPGA) or digital signal processor (DSP).

The filter options include the following:

• A low ripple FIR filter with a ±0.005 dB pass-band ripple to 102.4 kHz.
• A low latency sinc5 filter with up to a 1.024 MHz data rate to maximize control loop responsiveness.
• A low latency sinc3 filter that is fully programmable, with 50 Hz/60 Hz rejection capabilities.

When using the AD7768-1, embedded analog functionality within the AD7768-1 greatly reduces the design burden over the entire application range. The precharge buffer on each analog input decreases the analog input current compared to competing products, simplifying the task of an external amplifier to drive the analog input.

A full buffer input on the reference reduces the input current, providing a high impedance input for the external reference device or in buffering any reference sense resistor scenarios used in ratiometric measurements.

The device operates with a 5.0 V AVDD1 − AVSS supply, a 2.0 V to 5.0 V AVDD2 − AVSS supply, and a 1.8 V to 3.3 V IOVDD − DGND supply.

In low power mode, the AVDD1, AVDD2, and IOVDD supplies can run from a single 3.0 V rail.

The device requires an external reference. The absolute input reference (REF_IN) voltage range is 1 V to AVDD1 − AVSS.

The specified operating temperature range is −40°C to +125°C. The device is housed in a 4 mm × 5 mm, 28-lead LFCSP.

Note that, throughout this data sheet, multifunction pins, such as XTAL2/MCLK, are referred to either by the entire pin name or by a single function of the pin, for example, MCLK, when only that function is relevant.

Applications

• Platform ADC to serve a superset of measurements and sensor types
  • Sound and vibration, acoustic, and material science research and development
  • Control and hardware in loop verification
  • Condition monitoring for predictive maintenance
  • Electrical test and measurement
  • Audio testing and current and voltage measurement
  • Clinical electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (ECG) vital signs monitoring
  • USB-, PXI-, and Ethernet-based modular DAQ
  • Channel to channel isolated modular DAQ designs

The AD7386/AD7387/AD7388 are 16-bit, 14-bit, and 12-bit dual, simultaneous sampling, high speed, successive approximation register (SAR), analog-to-digital converters (ADCs) that operate from a 3.0 V to 3.6 V power supply and feature throughput rates of up to 4 MSPS. The analog input types are single-ended and are sampled and converted on the falling edge of CS.

The AD7386/AD7387/AD7388 have an on-chip sequencer and integrated on-chip oversampling block to improve dynamic range and reduce noise at lower bandwidths. Abuffered internal 2.5 V reference is included. Alternatively, an external reference up to 3.3 V can be used. The conversion process and data acquisition use standard control inputs, allowing interfacing to microprocessors or digital signal processors (DSPs). The AD7386 is compatible with 1.8 V, 2.5 V, and 3.3 V interfaces by using the separate logic supply.

The AD7386/AD7387/AD7388 are available in a 16-lead LFCSP with operation specified from −40°C to +125°C.

Product Highlights

1. 4-channel, dual simultaneous sampling ADC.
2. Pin-compatible product family.
3. High 4 MSPS throughput rate.
4. Space-saving 3 mm × 3 mm LFCSP.
5. Integrated oversampling block to increase dynamic range and SNR and to reduce SCLK speed requirements.
6. Single-ended analog inputs.
7. Small sampling capacitor reduces amplifier drive burden.

Applications

• Motor control position feedback
• Motor control current sense
• Sonar
• Power quality
• Data acquisition systems
• Erbium doped fiber amplifier (EDFA) applications
• Inphase and quadrature demodulation