RF Attenuator Self-Calibration for Sub-GHz Receive Chains
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Solution Overview
Problem
The calibration of attenuators in sub-GHz radio frequency signal receive chains is tedious and does not account for environmental disturbances affecting the antenna and impedance matching network, leading to inefficiencies in gain control.
Innovation Solution
A circuit with a controllable variable impedance and a current source that delivers a signal at the same frequency as the received signal, allowing for automated calibration by selecting impedance values based on output signals with and without the current source, thereby adapting gain to signal power while accounting for environmental impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods using external sub-GHz signal transmission are employed, then attenuation values can be determined, but the process becomes tedious and requires an anechoic environment while not accounting for environmental disturbances
Solution Approach 1:
The patent introduces an intermediary current source that generates calibration signals internally within the receive chain, eliminating the need for external signal transmission and anechoic environments. This current source acts as a mediator between the attenuator and the demodulation chain, providing test signals that account for environmental disturbances on the antenna and impedance matching network without requiring complex external calibration setups
Solution Approach 2:
The receive chain performs self-calibration by using its own internal components (current source, demodulation chain) to measure attenuation values. The system serves itself by generating calibration signals internally and processing them through the same signal path used for actual reception, thereby automatically accounting for environmental effects without requiring external calibration equipment or procedures
2Adaptability or versatility
If the receive chain gain is adapted by controlling the attenuator, then the receive chain can handle varying signal powers, but hysteresis effects occur and calibration becomes complex
Solution Approach 1:
The patent implements a feedback mechanism where the demodulation chain measures the calibration signals generated by the current source and provides information about the actual attenuation values. This feedback loop allows the system to determine precise attenuation values for each impedance setting and compensate for hysteresis effects, ensuring reliable gain control adaptability
Solution Approach 2:
The system performs preliminary calibration by measuring attenuation values for each attenuator impedance setting before actual signal reception. These pre-determined attenuation values are stored and used during operation to quickly adapt the receive chain gain without real-time calibration, reducing hysteresis effects and improving reliability
Data Source
AI summary
The present disclosure relates to a circuit including an input terminal configured to receive a first signal at a first frequency; a demodulation chain connected to the input terminal and including a low-noise amplifier having an input coupled to the terminal; a controllable variable impedance connected between a first node and a node configured to receive a reference potential, the first node being connected to the input terminal and/or to the amplifier input; and a current source configured to deliver a current at the first frequency to the first node.