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Analog Devices hearables and wearable solutions enable high value human experience through advanced interfaces and interpretation. System and platform offerings allow for a more immersive and natural interaction between people and technology while simultaneously extending battery life. Key system areas of focus are adaptive hybrid active noise cancellation (ANC), high fidelity audio capture and playback, ultrahigh efficiency device power management, and intuitive gesture. ADI’s innovation helps bring a competitive edge to hearable and wearable products.
High Quality, Low Power Audio Solutions
At ADI, we have used our extensive knowledge in high fidelity audio and applied that to the hearable and wearable market where size, cost, and power are key factors, while still ensuring but have ensured we still deliver best-in-class audio solutions.
Webinar: Active Noise Cancellation Technology for Wireless Headphones
This webcast highlights advanced ADI technologies embedded in earphone/headphones showing how consumer electronic devices can provide a differentiated feature set.
Noise Cancelling Without Compromise with Bowers & Wilkins
With the help of its longtime technology partner, Analog Devices, Bowers & Wilkins overcame daunting technical challenges, bringing its signature sound to a wider audience.
This demo highlights advanced ADI technologies embedded in earphone/headphones and shows how consumer electronic devices can provide a differentiated feature set.
Experience how the ADAU1787, a low-power codec with a programmable Fast DSP engine, can be used to build high-quality, low-power headphones with advanced features, including active noise cancellation.
This complete audio signal chain allows mobile device users to enjoy lossless, audiophile quality music limited only by their headphones. Featuring our audio DAC with our high performance amp (SSM6322) and low noise LDO regulators (ADP151, ADP7118, ADP7182).
Vital Signs Measurements and Wearable Health Monitors
Analog Devices’ vital sign measurement solutions are powered by a range of integrated and discrete sensor and signal conditioning technology solutions for portable, wearable, and bedside monitoring systems.
Non-contact Vital Sign Monitoring by Analog Devices
Analog Devices has built a noncontact vital sign monitoring (VSM) system to increase patient convenience.
Design a wearable health monitoring device such as a fitness band, sports watch, or pedometer by using ADI’s optical, impedance, biopotential, and motion sensor technologies and signal conditioning expertise.
Personal Electronics Software, Algorithms, and Tools
Experience high quality voice technology utilizing speech processing solutions from Analog Devices that enables you to hear clear and crisp speech even in a noisy environment. Intelligently focus on the speaker, eliminate annoying echoes and double talk, suppress noise, and enjoy superior sound using robust solutions from Analog Devices.
Speech Processing Solutions
The versatile speech processing solutions from Analog Devices enable a wide range of applications such as basic communications, gaming, conferencing solutions, and voice UI.
The SigmaStudio® graphical development tool is the programming, development, and tuning software for the SigmaDSP® and SHARC® audio processors and A2B® transceivers. Familiar audio processing blocks can be wired together as in a schematic, and the compiler generates DSP-ready code and a control surface for setting and tuning parameters.
The ADAU1787 is a codec with four inputs and two outputs that incorporates two digital signal processors (DSPs). The path from the analog input to the DSP core to the analog output is optimized for low latency and is ideal for noise cancelling headsets. With the addition of just a few passive components, the ADAU1787 provides a complete headset solution.
Note that throughout the data sheet, multifunction pins, such as BCLK_0/MP1, are referred to either by the entire pin name or by a single function of the pin, for example, BCLK_0, when only that function is relevant.
Applications
Noise cancelling handsets, headsets, and headphones
The ADAU1788 is a codec with two inputs and one output that incorporates two digital signal processors (DSPs). The path from the analog input to the DSP core to the analog output is optimized for low latency and is ideal for noise cancelling headsets. With the addition of just a few passive components, the ADAU1788 provides a noise cancelling headphone solution.
Note that throughout this data sheet, multifunction pins, such as BCLK_0/MP1, are referred to either by the entire pin name or by a single function of the pin, for example, BCLK_0, when only that function is relevant.
Applications
Noise cancelling handsets, headsets, and headphones
The ADAU1860 is a codec with three inputs and one output that incorporates two digital signal processors (DSPs). The path from the analog input to the DSP core to the analog output is optimized for low latency and is ideal for noise canceling earphone. With the addition of just a few passive components, the ADAU1860 provides a complete earphone solution.
APPLICATIONS
Noise canceling handsets, headsets, and headphones
Bluetooth active noise canceling (ANC) handsets, headsets, and headphones
The ADAU1850 is a codec with three inputs and one output that incorporates one digital signal processor. The path from the analog input to the DSP core to the analog output is optimized for low latency and is ideal for noise canceling earphones. With the addition of a few passive components, the ADAU1850 provides a complete headset solution.
The ADAU1850 is provided in a small, 28-ball, 2.957 mm × 1.757 mm wafer level chip scale package (WLCSP).
APPLICATIONS
Noise canceling handsets, headsets, and headphones
Bluetooth active noise canceling (ANC) handsets, headsets, and headphones
The ADPD144RI is a highly integrated, photometric front end optimized for photoplethysmography (PPG) detection of blood oxygenation (SpO2) by synchronous detection in red and infrared wavelengths. Synchronous measurement allows rejection of both dc and ac ambient light interference with extremely low power consumption.
The module combines highly efficient, light emitting diode (LED) emitters and a sensitive 4-channel, deep diffusion photodiode (PD1 to PD4) with a custom application specific integrated circuit (ASIC) in a compact package that provides optical isolation between the integrated LED emitters and the detection photodiodes to improve through tissue, signal-tonoise ratio (SNR).
The ASIC consists of a 4-channel analog front end (AFE) with two independently configurable datapaths with separate gain and filter settings, a 14-bit analog-to-digital converter (ADC) with a burst accumulator, two flexible, independently configurable, LED drivers, and a digital control block. The digital control block provides AFE and LED timing, signal processing, and communication. Data output and functional configuration occur over a 1.8 V I2C interface.
The LTC3337 is a primary battery state of health (SOH) monitor with a built-in precision coulomb counter. It is designed to be placed in series with a primary battery with minimal associated series voltage drop. The patented infinite dynamic range coulomb counter tallies ALL accumulated battery discharge and stores it in an internal register accessible via an I2C interface. A discharge alarm threshold based on this state of charge (SOC) is programmable. When it is reached, an interrupt is generated at the IRQ pin. Coulomb counter accuracy is constant down to no load.
The LTC3337 also integrates additional SOH monitoring which measures and reports via I2C: battery voltage, battery impedance, and temperature.
To accommodate a wide range of primary battery inputs, the peak input current limit is pin selectable from 5mA to 100mA.
Coulombs can be calculated for either the BAT_IN or BAT_OUT pin, determined by the AVCC pin connection.
A BAL pin is provided for applications utilizing a stack of two supercapacitors (optional) at the output.
The LTC3337 is offered in a 12-lead 2mm × 2mm LFCSP package.
APPLICATIONS
Low Power Primary Battery Powered Systems
(e.g., 1× LiSOCl2, 2–3× Alkaline)
The ADP5301 is a high efficiency, ultralow quiescent current step-down regulator that draws only a 180 nA quiescent current to regulate the output at no load.
The ADP5301 runs from an input startup voltage range of 2.15 V to 6.50 V, allowing the use of multiple alkaline/NiMH, Li-Ion cells, or other power sources. The output voltage is selectable from 0.8 V to 5.0 V by an external VID resistor and factory fuse. The total solution requires only four tiny external components.
The ADP5301 can operate between hysteresis mode and PWM mode via the SYNC/MODE pin. The regulator in hysteresis mode achieves excellent efficiency at a power of less than 1 mW and provides up to 50 mA of output current. The regulator in PWM mode produces a lower output ripple and supplies up to 500 mA of output current. The flexible configuration capability during operation of the device enables very efficient power management to meet both the longest battery life and low system noise requirements.
The ADP5301 contains a VOUTOK flag, which monitors the output voltage and runs at a 2 MHz switching frequency in PWM mode. SYNC/MODE can synchronize to an external clock from 1.5 MHz to 2.5 MHz.
Other key features in the ADP5301 include separate enabling, quick output discharge (QOD), and safety features such as overcurrent protection (OCP), thermal shutdown (TSD), and input undervoltage lockout (UVLO).
The ADP5301 is available in a 9-ball, 1.65 mm × 1.87 mm WLCSP rated for a −40°C to +125°C junction temperature range.
The combination of parts shown in Figure 1 provides an ultralow power, 3-axis, motion activated power switch solution capable of controlling up to 1.1 A of load current. The circuit is ideal for applications where extended battery life is critical. When the switch is off, the battery current is less than 300 nA, and when the switch is on, it draws less than 3 μA. The circuit provides an industry leading, low power motion sensing solution suitable for wireless sensors, metering devices, home healthcare, and other portable applications.
The 3-axis accelerometer controls the high-side switch by monitoring the acceleration in three axes and closes or opens the switch depending on the presence or absence of motion.
The ADXL362 is an ultralow power, 3-axis accelerometer that consumes less than 100 nA in wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by under sampling; it samples continuously at all data rates. There is also an on-chip, 12-bit temperature sensor accurate to ±0.5°.
The ADXL362 provides 12-bit output resolution and has three operating ranges, ±2 g, ±4 g, and ±8 g. It is specified over a minimum temperature range of −40°C to +85°C. For applications where a noise level less than 480 μg/√Hz is desired, either of its two lower noise modes (down to 120 μg/√Hz) can be selected at a minimal increase in supply current.
The ADP195 is a high-side load switch designed for operation between 1.1 V and 3.6 V and is protected against reverse current flow from output to input. The device contains a low on-resistance, P-channel MOSFET that supports over 1.1 A of continuous load current and minimizes power losses.
Figure 1. Ultralow Power Standalone Motion Switch (Simplified Schematic: Decoupling and All Connections Not Shown)
Basic Operation of the ADXL362
The ADXL362 is a three-axis, ultralow power acceleration measurement system capable of measuring dynamic acceleration (resulting from motion or shock) as well as static acceleration (that is, gravity).
The moving component of the sensor is a polysilicon, surface micromachined structure, also referred to as a beam, built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces.
Deflection of the structure is measured using differential capacitors. Each capacitor consists of independent fixed plates and plates attached to the moving mass. Any acceleration deflects the beam and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation is used to determine the magnitude and polarity of the acceleration.
Modes of Operation
The three basic modes of operation for the ADXL362 are standby, measurement, and wake-up.
Placing the ADXL362 in standby mode suspends measurement and reduces current consumption to 10 nA. Any pending data or interrupts are preserved; however, no new information is processed. The ADXL362 powers up in standby mode with all sensor functions turned off.
Measurement mode is the normal operating mode of the ADXL362. In this mode, acceleration data is continuously read, and the accelerometer consumes less than 3 μA across its entire range of output data rates of up to 400 Hz using a 2.0 V supply. All described features are available while operating in this mode. The ability to continuously output data from the minimum 12.5 Hz to the maximum 400 Hz data rate while still delivering less than 3 μA of current consumption is what defines the ADXL362, as an ultralow power accelerometer. Under sampling and aliasing do not occur with the ADXL362. because it continuously samples the full bandwidth of its sensor at all data rates.
Wake-up mode is ideal for simple detection of the presence or absence of motion at extremely low power consumption (270 nA at a 2.0 V supply voltage). Wake-up mode is useful particularly for implementation of a motion-activated on/off switch, allowing the rest of the system to be powered down until activity is detected. Wake-up mode reduces current consumption to a very low level by measuring acceleration only 6 times a second to determine whether motion is present. In wake-up mode, all accelerometer features are available with the exception of the activity timer. All registers are accessible, and real-time data is available from the part.
The CN0274 evaluation software uses the wake-up mode of the ADXL362. That is, the ADXL362 is asleep until it detects motion at which point it enters measurement mode.
Power/Noise Tradeoff
The ADXL362 offers a few options for decreasing noise at the expense of only a small increase in current consumption.
The noise performance of the ADXL362 in normal operation, typically 7 LSB rms at 100 Hz bandwidth, is adequate for most applications, depending upon bandwidth and the desired resolution. For cases where lower noise is needed, the ADXL362 provides two lower noise, operating modes that trade reduced noise for somewhat higher supply current.
Table 1. Specified and Measured Supply Currents
Mode
Noise (µg/√Hz Typical)
Current Consumption (µA Typical)
Normal Operation
380
2.7
Low Noise
280
4.5
Ultralow Noise
175
15
Table 1 shows the supply current values and noise densities obtained for normal operation and the two lower noise modes, at a typical 3.3 V supply.
The CN0274 evaluation software uses the normal operation noise mode of the ADXL362.
Motion Detection
The ADXL362 has built-in logic that detects activity (acceleration above a certain threshold) and inactivity (lack of acceleration above a certain threshold).
Detection of an activity or inactivity event is indicated in the status register and can also be configured to generate an interrupt. In addition, the activity status of the device, that is, whether it is moving or stationary, is indicated by the AWAKE bit.
Activity and inactivity detection can be used when the accelerometer is in either measurement mode or wake-up mode.
Activity Detection
An activity event is detected when acceleration stays above a specified threshold for a user-specified time period. The two activity detection events are absolute and referenced.
When using absolute activity detection, acceleration samples are compared to a user set threshold to determine whether motion is present. For example, if a threshold of 0.5 g is set, and the acceleration on any axis is 1 g for longer than the user defined activity time, the activity status is asserted. In many applications, it is advantageous for activity detection to be based not on an absolute threshold but on a deviation from a reference point or orientation. This is particularly useful because it removes the effect on activity detection of the static 1 g imposed by gravity. When an accelerometer is stationary, its output can reach 1 g, even when it is not moving. In absolute activity, if the threshold is set to less than 1 g, activity is immediately detected in this case.
In the referenced activity detection, activity is detected when acceleration samples are at least a user set amount above an internally defined reference, for the user defined amount of time. The reference is calculated when activity detection is engaged, and the first sample obtained is used as a reference point. Activity is only detected when the acceleration has deviated sufficiently from this initial orientation. The referenced configuration results in a very sensitive activity detection that detects even the most subtle motion events.
The CN0274 evaluation software uses the referenced mode of operation when searching for activity.
Inactivity Detection
An inactivity event is detected when acceleration remains below a specified threshold for a specified time. The two inactivity detection events are absolute and referenced.
In absolute inactivity detection, acceleration samples are compared to a user set threshold for the user set time to determine the absence of motion.
In referenced inactivity detection, acceleration samples are compared to a user specified reference for a user defined amount of time. When the part first enters the awake state, the first sample is used as a reference point, and the threshold is applied around it. If the acceleration stays inside the threshold, the part enters the asleep state. If an acceleration value moves outside the threshold, this point is then used as a new reference, and the thresholds are reapplied to this new point.
The CN0274 evaluation software uses the referenced mode of operation when searching for inactivity.
Linking Activity and Inactivity Detection
The activity and inactivity detection functions can be used concurrently, and processed manually by a host processor, or they can be configured to interact in several ways:
In default mode, activity and inactivity detection are both enabled, and all interrupts must be serviced by a host processor; that is, a processor must read each interrupt before it is cleared and can be used again.
In linked mode, activity and inactivity detection are linked to each other such that only one of the functions is enabled at any given time. Once activity is detected, the device is assumed moving or awake and stops looking for activity: inactivity is expected as the next event so only inactivity detection operates. When inactivity is detected, the device is assumed stationary or asleep. Activity is now expected as the next event so that only activity detection operates. In this mode, a host processor must service each interrupt before the next is enabled.
In loop mode, motion detection operates as previously described in linked mode; however, interrupts do not need to be serviced by a host processor. This configuration simplifies the implementation of commonly used motion detection and enhances power savings by reducing the amount of power used in bus communication.
When enabling autosleep mode in linked mode or loop mode, it causes the device to autonomously enter wake-up mode when inactivity is detected, and reenter measurement mode when activity is detected.
The CN0274 evaluation software uses the autosleep and loop modes to demonstrate the functionality of the ADXL362.
The AWAKE Bit
The AWAKE bit is a status bit that indicates whether the ADXL362 is awake or asleep. The device is awake when it has seen an activity condition, and the device is asleep when it has seen an inactivity condition.
The awake signal can be mapped to the INT1 or INT2 pin and can thus be used as a status output to connect or disconnect power to downstream circuitry based on the awake status of the accelerometer. Used in conjunction with loop mode, this configuration implements a trivial, autonomous motion-activated switch.
If the turn-on time of the downstream circuitry can be tolerated, this motion switch configuration can save significant system-level power by eliminating the standby current consumption of the rest of the application. This standby current can often exceed the full operating current of the ADXL362.
Interrupts
Several of the built-in functions of the ADXL362 can trigger interrupts to alert the host processor of certain status conditions.
Interrupts may be mapped to either (or both) of two designated output pins, INT1 and INT2, by setting the appropriate bits in the INTMAP1 and INTMAP2 registers. All functions can be used simultaneously. If multiple interrupts are mapped to one pin, the OR combination of the interrupts determines the status of the pin.
If no functions are mapped to an interrupt pin, that pin is automatically configured to a high impedance (high-Z) state. The pins are placed in this state upon a reset as well.
When a certain status condition is detected, the pin that condition is mapped to is activated. The configuration of the pin is active high by default, so that when it is activated, the pin goes high. However, this configuration can be switched to active low by setting the INT_LOW pin in the appropriate INTMAP register.
The INT pins may be connected to the interrupt input of a host processor and interrupts responded to with an interrupt routine. Because multiple functions can be mapped to the same pin, the STATUS register can be used to determine which condition caused the interrupt to trigger.
The CN0274 evaluation software configures the ADXL362 such that when activity is detected, the INT1 pin is high, and when inactivity is detected, the INT1 pin is low.
Test Results
All testing was performed using the EVAL-CN0274-SDPZ and the EVAL-SDP-CS1Z. Functionality of the part is demonstrated by setting the activity threshold at 0.5 g, the inactivity threshold at 0.75 g, and the number of inactivity samples at 20. When looking for activity, only one acceleration sample on any axis is required to cross the threshold.
Starting with the circuit oriented so that the battery pack is flat against the table, the printed circuit board (PCB) can be slowly rotated 90° in any direction causing the acceleration to cross the threshold as it approaches perpendicular to the initial orientation.
Figure 2 shows a screen shot of the CN0274 evaluation software showing the ADXL362 first asleep, looking for activity. Then, when Sample 11 crosses the threshold, the ADXL362 enters the awake state and begins looking for inactivity. The thresholds adjust to show the device is now looking for inactivity.
Figure 2. Screen Shot of Evaluation Software Output
For better visibility, the X-axis and Z-axis plots are disabled using the radio buttons above the chart.
The output of the ADP195, or the interrupt pin itself, was measured using a digital multimeter. When the ADXL362 is awake, the interrupt goes high and drives the EN pin of the ADP195, high, which in turn drives the gate of the MOSFET low, causing the switch to close, connecting any downstream circuitry to the power supply. Conversely, when the ADXL362 is asleep, the interrupt drives the EN pin of the ADP195 low, which in turn drives the gate of the MOSFET high, causing the switch to open.
PCB Layout Considerations
In any circuit where accuracy is crucial, it is important to consider the power supply and ground return layout on the board. The PCB should isolate the digital and analog sections as much as possible. The PCB for this system was constructed in a 4-layer stack up with large area ground plane layers and power plane polygons. See the MT-031 Tutorial for more discussion on layout and grounding, and the MT-101 Tutorial for information on decoupling techniques.
Decouple the power supply to the ADXL362 with 1 μF and 0.1 μF capacitors to properly suppress noise and reduce ripple. Place the capacitors as close to the device as possible. Ceramic capacitors are advised for all high frequency decoupling.
Power supply lines should have as large a trace width as possible to provide low impedance paths and reduce glitch effects on the supply line. Shield clocks and other fast switching digital signals from other parts of the board by digital ground. A photo of the PCB is shown in Figure 3.
The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either an SPI (3- or 4-wire) or I2C digital interface.
The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing appli-cations, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes of about 0.25°. Using a digital output accelerometer such as the ADXL345 eliminates the need for analog-to-digital conversion, reducing system cost and real estate. Additionally, the ADXL345 includes a variety of built-in features. Activity/inactivity detection, tap/double-tap detection, and free-fall detection are all done internally with no need for the host processor to perform any calculations. A built-in 32-stage FIFO memory buffer reduces the burden on the host processor, allowing algorithm simplification and power savings. Additional system level power savings can be implemented using the built-in activity/inactivity detection and by using the ADXL345 as a “motion switch” to turn the whole system off when no activity is felt and on when activity is sensed again.
The ADXL345 communicates via I2C or SPI interface. The circuits described in this document demonstrate how to implement communication via these protocols.
Figure 1. ADXL345 and ADuC7024 in 4-Wire SPI Configuration (Simplified Schematic: Decoupling and All Connections Not Shown)
Figure 2. ADXL345 and ADuC7024 in I2C Configuration (Simplified Schematic: Decoupling and All Connections Not Shown)
The circuit shown in Figure 1 is a complete low cost, low power, mono audio amplifier with volume control, glitch reduction, and a 3 W Class-D output driver.
The volume is controlled manually with a simple push-button interface to a 64-position digital potentiometer. An automatic store function retains the last volume setting, and an LED provides visual information of the maximum/minimum volume.
The SSM2375 Class-D driver amplifier provides up to 3 W output power into 3 Ω load, with 93% power efficiency at 5 V, built in pop and click suppression, and shutdown mode.
The circuit provides a preconditioning input stage, allowing compatibility with a wide range of audio input signals and can be powered with a cell battery.
Figure 1. Audio Volume Control (Simplified Schematic: Decoupling and All Connections Not Shown)
