Wireless Transmitter Driver Envelope Control for ASK Pulse Distortion
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Solution Overview
Problem
RFID and NFC systems face distortion issues due to the loading effect from receiver antennas, leading to overshoots and undershoots in modulation pulses, which conventional solutions cannot address for ASK modulation.
Innovation Solution
A method involving a driver that switches between two voltage supplies with the same level, using a modulation index value to configure the second voltage during the modulated state, and filtering to prevent overshoots and undershoots, allowing for smooth transitions between non-modulated and modulated states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional switching between voltage levels is used to reduce modulation distortion, then rising and falling edge duration increases, but non-monotonic waveshapes are generated that cannot be used for ASK modulation
Solution Approach 1:
The patent applies preliminary action by pre-configuring the modulation index value to set the second voltage level equal to the first voltage level before switching occurs. This preparatory step ensures that when switching between voltage supplies, both supplies are at the same level, eliminating abrupt transitions and preventing non-monotonic waveshapes. The modulation index is adjusted in advance to match the load conditions, allowing smooth transitions compatible with ASK modulation requirements.
2Power
If the driver supply is switched between non-carrier and carrier levels during modulation edges, then modulation depth increases, but overshoots and undershoots are generated due to loading effects
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the modulation index value based on loading effects detected from the receiver antenna. The modulation index is configured to set the second voltage level according to the actual load conditions, allowing the system to adapt the voltage transition parameters in real-time. This dynamic parameter adjustment compensates for loading effects and prevents overshoots and undershoots while maintaining adequate modulation depth.
Solution Approach 2:
The system implements feedback by monitoring the loading effects from the receiver antenna and using this information to adjust the modulation index value. The configurable modulation index is determined based on the detected load conditions, creating a closed-loop control system that continuously optimizes the voltage transition to maintain signal envelope shape accuracy despite varying antenna loading.
3Adaptability or versatility
If a configurable modulation index is introduced to adapt to unknown receiver antennas, then adaptability improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the driver to accept a configurable modulation index parameter that can be adjusted to accommodate different receiver antenna types and loading conditions. The same driver circuit can serve multiple modulation standards (OOK and ASK) and work with various antenna configurations by simply changing the modulation index value, eliminating the need for multiple dedicated circuits for different scenarios.
Data Source
AI summary
A method for controlling a signal envelope shape of modulation pulses in a driver of a wireless transmitter includes supplying a first voltage to the driver during a non-modulated state, supplying a second voltage configurable by a configurable modulation index value to the driver during a modulated state, switching between the non-modulated state and the modulated state comprising setting the modulation index value to configure the second voltage level at the same level as the first voltage and then switching between supplying the first voltage to the driver and supplying the second voltage to the driver, and filtering to a limited bandwidth the variations of the second voltage resulting from configuring the modulation index value.