Analog Front-End
Operational Amplifiers
Analog sensors need signal transducers to deliver the information to the MCU. These signal transducers should have following key features
- Accurate and stable to guarantee the maximum precision of the information
- Low power to guarantee a longer user experience
- Small to be integrated in the most stylish and thin designs
A low input offset voltage with zero drift amplifiers is mandatory. Otherwise the electrodes information would be less accurate or lost. Once the signal dynamic has been restored precision and micro power consumption amplifiers are needed before the signal is fed to the MCU
Switches
Switches allow multiplexing or de-multiplexing a great variety of signals. Wearable devices are experiencing a sensors proliferation and switches are can be used to route signals from/towards them. Switches are also used to route signals such as audio to speaker or to the headphones. ST Analog switches line up is meant to cover all the possible signal typologies from audio to USB so to fit most of the application needs
Audio
MEMS Microphone
MEMS Microphone is audio sensor that converts sound signals into electrical signals. MEMS Microphones are increasingly preferred over conventional microphones as they offer higher SNR, small form factor, digital interface, better RF immunity and high robustness against vibration.
Microphone makes the interaction easier, faster and smoother. It also enables fashionable and stylish designs by reducing the number of buttons.
Analog MEMS Microphone: Bottom port with high bandwidth, omnidirectional and high SNR
Next microphones trend is to allow dual mode operations
- Sniffing/low power mode: the device reduces the power consumption at minimum whilst guaranteeing an adequate set of performances for voice activity detection.
- Normal mode: the acoustical parameters are set to the optimal level for voice control applications.
With the help of Switch Microphone can be put is sniff/normal mode by microcontroller
Audio Amplifier
Audio Amplifiers are needed to drive speakers for sound output for songs, communication or alerts. Highly-efficient audio amplifiers capable of delivering high quality audio into small and low power devices is a desired features in many wearable devices.
Power Management
- Battery Monitoring
As wearable devices are run by small battery, it is imperative to use the battery in most optimised way. An accurate battery monitoring allows knowing exact state of charge of battery and add intelligence in its usage. For eg: giving timely alert to the user or turning off the power consuming blocks when battery is low. ST’s STC3115 is an integrated solution capable of combining current integration and voltage variation over the time thus providing the most accurate battery status measurement
| STC3115 : 0.25 % accuracy battery monitoring IC
·      Coulomb counter and voltage-mode gas gauge ·      Robust initial open-circuit-voltage (OCV) ·      Low battery level alarm output ·      Internal temperature sensor ·      Battery swap detection ·      1.4 x 2.0 mm 10-bump CSP package |
Smart RESET
As the wearable devices get smarter day by day the software complexity grows exponentially in order to manage all the sensor information. As the number of features increases, the possibility of and end-user misuse of the product increases accordingly. System crashes are likely to happen and it is mandatory to provide an escape sequence to restart the application and maintain a perception of quality and brand recognitions.
STM6519 IC can be used to implement two functionalities from single button
