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, which causes overshoots and undershoots in modulation pulses, particularly when using ASK modulation, as conventional solutions fail to address these issues effectively.
Innovation Solution
A method involving a driver for a wireless transmitter that switches between two voltage supplies of the same level, with a configurable modulation index, and filters the variations to prevent overshoots and undershoots, allowing for smooth edge transitions independent of antenna load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional switching solution is used to reduce modulation distortion, then rising and falling edge duration is extended, but non-monotonic waveshapes are generated that are incompatible with ASK modulation
Solution Approach 1:
The patent applies preliminary action by pre-configuring the modulation index value to match the supply voltage level before switching occurs. When transitioning between modulated and non-modulated states, the modulation index is set to the same value as the supply voltage, ensuring that no voltage step occurs at the switching instant. This preliminary configuration prevents the generation of non-monotonic waveshapes and eliminates both overshoots and undershoots, making the solution compatible with ASK modulation while maintaining waveform quality.
2Reliability
If driver supply is switched between non-carrier and carrier levels during modulation edges, then modulation distortion is reduced, but the solution only works for OOK modulation and creates non-monotonic waveshapes
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the modulation index value based on the modulation type and supply voltage level. Instead of using fixed supply levels, the modulation index is configured to match the supply voltage before switching, and this parameter is adaptively changed for different modulation types (OOK, ASK, etc.). This parameter adaptation enables the solution to work across multiple modulation types while maintaining pulse accuracy and eliminating distortion.
3Reliability
If modulation index is configured at the same level as supply voltage before switching, then overshoots and undershoots are eliminated, but additional control complexity is introduced
Solution Approach 1:
The patent applies feedback by continuously monitoring the supply voltage level and using this information to automatically configure the modulation index value. The system reads the supply voltage, compares it with the required modulation index, and adjusts the modulation index accordingly before switching events. This feedback mechanism eliminates the need for complex external control circuits, as the system self-regulates to maintain accurate signal envelope shapes without overshoots or undershoots.
Data Source
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AI summary
The method for controlling a signal envelope shape of modulation pulses in a driver (TX_DR) of a wireless transmitter (TX), includes: - supplying a first voltage (VDD_RF) to the driver during a non-modulated state, - supplying a second voltage (VDD_ASK) 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 (VDD ASK) at the same level as the first voltage (VDD_RF) and then switching between supplying the first voltage (VDD_RF) to the driver and supplying the second voltage (VDD ASK) to the driver, and - filtering to a limited bandwidth the variations of the second voltage resulting from configuring the modulation index value.