Wake-Up Timer Calibration Using Dual Oscillators for Beacon Timing
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Solution Overview
Problem
Low precision in wake-up timers for wireless devices leads to unnecessary early activations, wasting energy as they power up too early to ensure beacon signals are not missed, especially in devices with limited battery life like those using coin cells.
Innovation Solution
A system that uses a combination of low-power and crystal oscillators to determine sleep times with greater precision by measuring the time between specific events in received signals, allowing the low-power oscillator to handle most of the sleep period and switching to the crystal oscillator closer to the expected beacon arrival for higher precision, thereby reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the wake-up timer uses a low-power oscillator to extend battery life, then power consumption is reduced, but timing precision deteriorates causing unnecessary early wake-ups
Solution Approach 1:
The wake-up timer functionality is segmented into two parts: a low-power oscillator handles the majority of the sleep period timing, while a high-precision crystal oscillator is activated only for the final portion before the expected beacon arrival. This segmentation allows the system to use the power-efficient low-power oscillator for most of the time while relying on the precise crystal oscillator only when needed for accurate wake-up timing.
Solution Approach 2:
The system dynamically switches between two oscillator modes based on the remaining time until the expected beacon arrival. During the majority of the sleep period, the low-power oscillator is active. As the expected wake-up time approaches, the system transitions to using the crystal oscillator for the final calibration and wake-up execution, optimizing both power consumption and timing precision dynamically.
2Reliability
If the receiver circuit powers up early to ensure beacon signals are not missed, then reliability of beacon reception is improved, but energy waste increases
Solution Approach 1:
The system replaces the mechanical approach of always powering up early with a calibrated timing system that uses oscillator pulse counting to determine the precise wake-up moment. By measuring the actual interval between beacons and calculating the exact wake-up time based on oscillator pulses, the system can reliably catch beacons without unnecessary early activation, substituting brute-force early wake-up with precision timing.
Solution Approach 2:
The system changes the timing parameter dynamically based on measured beacon intervals. Instead of using a fixed early wake-up time, the system measures the actual beacon interval and adjusts the wake-up time parameter accordingly, using oscillator pulse counts to achieve precise timing that adapts to actual beacon transmission patterns, thereby eliminating energy waste from consistently early wake-ups.
Data Source
AI summary
A wireless transceiver includes receiver front-end circuitry for processing an ingoing radio frequency (RF) signal to produce an in-going digital signal to a processor connected to receive the in-going digital signal. The processor includes sync word determination logic configured to identify a received sync word or other event or connection point and to subsequently generate an event determination signal. A low power oscillator produces low frequency pulses to a first counter. A crystal oscillator that produces higher frequency pulses to a second counter is used for the last portion of the desired sleep time for greater resolution. Thus, a calibration controller receives pulse counts from at least one of the first and second counters and determines a period between a common event of subsequent beacon signals or connection events and determines wake up times based on the received pulse counts from at least one of the first and second counters.