Subthreshold Wake-Up Receiver With Automatic Interference Rejection
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Solution Overview
Problem
Existing wake-up radios (WRXs) face challenges in reducing power consumption while avoiding false wake-ups due to interference, as they often require high power to differentiate between wake-up signals and interference, which can lead to significant energy wastage in wireless sensors.
Innovation Solution
A low power wake-up receiver with automatic interference rejection is developed, utilizing a subthreshold design, including a Dickson Multiplier circuit, correlator, and automatic threshold control, which adjusts sensitivity dynamically to reject interference and reduce power consumption, allowing operation in the nanowatt range with a selectable 31-bit code for wake-up signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If energy detection architecture is used to reduce WRX power, then power consumption is reduced, but false wake-ups occur due to interference
Solution Approach 1:
The patent implements automatic threshold feedback that continuously monitors the received signal and dynamically adjusts the wake-up threshold. When interference is detected (high energy without valid code), the threshold is automatically increased to prevent false wake-ups, while maintaining low power operation. This feedback mechanism resolves the contradiction by adapting the detection sensitivity based on actual interference conditions.
Solution Approach 2:
The patent introduces a code correlation intermediary between the energy detector and the wake-up decision. Instead of directly triggering on energy detection, the system correlates the received signal with expected wake-up codes. This intermediary step filters out interference that doesn't match valid codes while preserving sensitivity to legitimate wake-up signals, eliminating false wake-ups without requiring high power operation.
2Use of energy by moving object
If sensitivity is reduced to lower WRX power, then power consumption decreases, but communication range and reliability are limited
Solution Approach 1:
The patent segments the signal processing into distinct functional blocks: RF front-end, energy detection, code correlation, and threshold control. Each segment is optimized for low power operation while contributing to overall sensitivity. The segmentation allows the system to achieve high effective sensitivity through the combination of multiple specialized low-power stages rather than relying on a single high-power sensitive receiver.
Solution Approach 2:
The patent implements dynamic threshold adjustment that adapts to changing signal and interference conditions. The threshold is not fixed but dynamically modified based on real-time analysis of the received signal characteristics. This dynamic behavior allows the system to maintain high sensitivity for weak valid signals while automatically raising the threshold to reject interference, effectively resolving the sensitivity-power contradiction.
3Reliability
If local processing is added to differentiate wake-up events from interference, then false wake-ups are prevented, but device complexity increases
Solution Approach 1:
The patent implements self-service local processing where the wake-up receiver autonomously performs interference rejection without requiring the main processor. The baseband processing includes automatic threshold adjustment and code correlation that self-regulate based on the received signal characteristics. This self-service capability provides robust interference rejection while keeping the processing simple and localized to the RF front-end, avoiding the need for complex external processing.
Data Source
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AI summary
A low power radio is provided with automatic interference rejection. The radio is comprised generally of: an antenna, a rectifier, a comparator, and a correlator. The comparator receives an input signal from the rectifier, compares the input signal to a reference signal and outputs a digital signal. The correlator in turn receives the digital signal from the comparator, correlates the digital signal to a wake-up code and outputs a wake-up signal having a high value when the digital signal is highly correlated with the wake-up code. The radio further includes an automatic threshold controller which adjusts sensitivity of the comparator. Of note, the rectifier, the comparator, the correlator and the automatic threshold controller are comprised in part by circuits having transistors operating only in subthreshold region.