Over-the-Air Oscillator Calibration for Low-Power BLE Frequency Locking
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Solution Overview
Problem
Low-power IoT devices face challenges in maintaining accurate frequency for wireless communication without a resonator, as existing solutions like RFID synchronization are not applicable for BLE transmitters with specific transmission sessions.
Innovation Solution
An oscillator calibration circuit using over-the-air reference signals to lock the frequency of oscillators before data transmission sessions, allowing them to remain free-running during transmission, thereby reducing power consumption and frequency drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a free-running oscillator is used in low-power IoT devices, then power consumption is reduced, but frequency accuracy deteriorates due to lack of resonator locking
Solution Approach 1:
The oscillator is pre-calibrated to a target frequency before data transmission sessions using over-the-air reference signals. This preliminary frequency alignment ensures accurate transmission without requiring continuous resonator locking, thereby reducing power consumption while maintaining frequency accuracy when needed.
Solution Approach 2:
Frequency calibration is performed periodically at the beginning of data transmission sessions rather than continuously. The oscillator operates in free-running mode between calibration events, consuming minimal power, then is briefly calibrated using received reference signals before each transmission session to ensure frequency accuracy.
2Measurement precision
If oscillator calibration is performed continuously, then frequency accuracy is improved, but power consumption increases
Solution Approach 1:
The calibration circuit operates periodically only during data transmission sessions rather than continuously. Reference signals are received and used for frequency calibration at the start of transmission sessions, after which the oscillator runs freely without continuous calibration, significantly reducing power consumption while maintaining accuracy when transmitting data.
Solution Approach 2:
Frequency calibration is performed in advance at the beginning of each data transmission session using over-the-air reference signals. This preliminary action ensures the oscillator is accurately frequency-aligned before data transmission begins, eliminating the need for continuous calibration and reducing overall power consumption.
3Measurement precision
If RFID synchronization method is used, then frequency alignment is achieved, but applicability deteriorates for BLE transmitters with specific transmission sessions
Solution Approach 1:
The calibration system is designed to be dynamically adaptable to BLE transmission session requirements. The calibration circuit receives over-the-air reference signals and performs frequency alignment specifically timed to coincide with BLE data transmission sessions, making the system versatile and applicable to the specific operational patterns of BLE devices rather than following fixed RFID-style synchronization.
Solution Approach 2:
The system changes its operational parameters to match BLE transmission session characteristics. Calibration is performed at specific times (beginning of transmission sessions) and uses reference signals received over-the-air, adapting the frequency alignment process to the dynamic nature of BLE communication patterns rather than using static RFID synchronization methods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution achieves high frequency accuracy and low power consumption in BLE transmitters by calibrating oscillators using over-the-air signals, eliminating the need for explicit resonators and minimizing frequency drift during transmission sessions.
Implementation Method 1
The oscillator generates a radio frequency (RF) carrier signal that may carry the data signal generated by the BLE packetizer
Implementation Method 2
The free running oscillator is locked via a phase-locked loop (PLL) to a clock, originating from a crystal oscillator
Implementation Method 3
The modulated RF signal, carrying the data signal, is amplified by the amplifier and then broadcast by the antenna
Data Source
AI summary
An oscillator calibration circuit is presented. The oscillator calibration includes a first frequency locking circuit (FLC) coupled to a first oscillator, wherein the first FLC calibrates the frequency of the first oscillator using an over-the-air reference signal, wherein the first FLC calibrates the first oscillator prior to a data transmission session and remains free running during the data transmission session; and a second FLC coupled to a second oscillator, wherein the second FLC calibrates the frequency of the second oscillator using the over-the-air reference signal, wherein the second FLC calibrates the second oscillator immediately prior to a data transmission session and remains free running during the data transmission session.