OTA Oscillator Calibration for Free-Running BLE Transmitters
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Solution Overview
Problem
Low-power IoT devices face challenges in reliable communication and power efficiency due to the reliance on batteries, and existing solutions for frequency calibration in Bluetooth Low Energy (BLE) transmitters are inadequate, particularly for devices without resonators.
Innovation Solution
An oscillator calibration circuit that uses over-the-air reference signals to calibrate oscillators prior to data transmission sessions, disabling frequency locking circuits during transmission to reduce power consumption and prevent frequency drift, allowing oscillators to operate freely and efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency locking circuits are continuously enabled to maintain frequency accuracy, then frequency stability is improved, but power consumption increases
Solution Approach 1:
The frequency locking circuit is enabled periodically only during calibration phases and disabled during normal operation. The system performs frequency calibration at specific intervals or events (e.g., when entering advertising mode or upon receiving connection requests) rather than continuously locking the oscillator, thereby achieving frequency accuracy when needed while minimizing power consumption during data transmission.
2Reliability
If resonators are included to provide stable frequency reference, then frequency stability is improved, but device size and cost increase
Solution Approach 1:
The patent extracts and removes the resonator component from the traditional oscillator design. Instead of using a physical resonator (crystal, ceramic, or MEMS) to provide frequency reference, the system uses a free-running oscillator combined with periodic frequency calibration through frequency locking circuits that reference external signals or previously stored frequency information, thereby achieving frequency stability without the size and cost overhead of resonators.
Solution Approach 2:
The system copies or emulates the frequency reference function that would traditionally be provided by a physical resonator. By using software-controlled frequency calibration and locking mechanisms that reference external signals or stored calibration data, the patent creates a virtual frequency reference that replicates the stabilizing effect of a resonator without requiring physical resonant components.
3Use of energy by moving object
If free-running oscillators are used to reduce power consumption, then power efficiency is improved, but frequency drift increases
Solution Approach 1:
The system performs preliminary frequency calibration actions before entering free-running mode. Frequency locking circuits are activated in advance to calibrate the oscillator frequency based on external reference signals or stored calibration data. This preliminary calibration ensures that when the oscillator transitions to free-running mode, it starts from an accurate frequency reference point, minimizing subsequent frequency drift while maintaining power efficiency.
Solution Approach 2:
The system implements feedback mechanisms where the frequency locking circuit periodically monitors and adjusts the oscillator frequency. External reference signals or previously calibrated frequency information are used as feedback to correct frequency drift in the free-running oscillator. This feedback loop maintains frequency accuracy over time while allowing the oscillator to operate in low-power free-running mode between calibration events.
Data Source
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Figure 3A~3D
AI summary
Oscillator calibration circuits and wireless transmitters including oscillator calibration circuits. An oscillator calibration circuit 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.