RF Transceiver Voltage Modulation for OFDM Envelope Tracking
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Solution Overview
Problem
In 5G-NR wireless communication systems, the inter-symbol power variation of RF signals poses a challenge for power management integrated circuits (PMICs) as they need to adapt the modulated voltage within the cyclic prefix of each OFDM symbol to avoid distortion, such as amplitude clipping, while ensuring accurate amplification of time-variant power envelopes.
Innovation Solution
A transceiver circuit dynamically performs inter-symbol and intra-symbol voltage modulation by generating multiple or single voltage targets based on the type of information carried in each symbol, enabling the PMIC to timely adapt the modulated voltage and track the time-variant power envelope of the RF signal, thereby preventing distortion and protecting critical information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the modulation bandwidth is increased to achieve higher data rates, then the data rate is improved, but the OFDM symbol duration becomes shorter making voltage adaptation more difficult
Solution Approach 1:
The patent segments the voltage modulation process into two distinct modes: inter-symbol voltage modulation (adjusting voltage between OFDM symbols) and intra-symbol voltage modulation (adjusting voltage within OFDM symbols during the cyclic prefix period). This segmentation allows the system to handle the shortened symbol duration by performing multiple voltage adjustments within the available time, effectively resolving the conflict between high data rates and short symbol durations
Solution Approach 2:
The patent implements dynamic voltage modulation where the voltage target is dynamically adjusted based on the instantaneous power envelope of the RF signal. The transceiver circuit determines voltage targets and the PMIC dynamically modulates the voltage supply to the power amplifier in real-time, allowing the system to adapt to the rapidly changing power requirements of high-bandwidth OFDM signals with shortened symbol durations
2Reliability
If the voltage modulation is performed within the cyclic prefix to avoid distortion, then the signal fidelity is improved, but the time available for voltage adaptation is reduced
Solution Approach 1:
The patent performs preliminary voltage modulation actions during the cyclic prefix period before the actual data-bearing OFDM symbol is transmitted. The transceiver circuit calculates the required voltage targets and the PMIC adjusts the voltage supply within the cyclic prefix time, preparing the power amplifier for the upcoming symbol. This preliminary action ensures that when the data symbol is transmitted, the voltage is already optimized, maintaining signal fidelity without requiring additional time beyond the cyclic prefix
Solution Approach 2:
The patent changes the voltage parameter dynamically within the cyclic prefix period to match the instantaneous power envelope of the RF signal. By adjusting the voltage target parameter in real-time during the cyclic prefix, the system achieves accurate voltage adaptation for the subsequent data symbol, maintaining signal fidelity while utilizing the limited time available in the shortened OFDM structure
3Reliability
If the PMIC adapts the modulated voltage to track the time-variant power envelope, then the distortion is avoided, but the complexity of the voltage control increases
Solution Approach 1:
The patent implements a feedback mechanism where the transceiver circuit monitors the power envelope of the RF signal and uses this information to determine the appropriate voltage targets. The PMIC receives these voltage targets and adjusts the voltage supply accordingly, creating a closed-loop control system. This feedback approach allows the system to automatically track the time-variant power envelope and avoid distortion without requiring overly complex control circuitry, as the voltage targets are derived from the actual signal characteristics
Solution Approach 2:
The patent introduces an intermediary voltage target calculation mechanism that bridges the gap between the RF signal power envelope and the PMIC voltage control. The transceiver circuit acts as an intermediary by calculating intermediate voltage target values based on the power envelope characteristics, which then guide the PMIC's voltage modulation. This intermediary approach simplifies the overall control complexity by breaking down the direct control task into manageable steps: power envelope detection, voltage target calculation, and PMIC voltage adjustment
Data Source
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Figure 3A~3B
AI summary
Circuit and method for inter-symbol and intra-symbol voltage method are disclosed. Herein, a transceiver circuit is configured to determine a voltage target(s) for generating a modulated voltage(s) to amplify a radio frequency (RF) signal modulated in multiple symbols. Specifically, the transceiver circuit will generate multiple voltage targets for any of the symbols to thereby enable intra-symbol voltage modulation when the respective symbol is modulated to carry a selected type of information or generate a single voltage target for any of the symbols to thereby enable inter-symbol voltage modulation when the respective symbol lacks the selected type of information. By dynamically performing inter-symbol and intra-symbol voltage modulation based on the type of information carried in a symbol(s), the modulated voltage can be timely adapted to closely track a time-variant power envelope of the RF signal to thereby avoid potential distortion and protect critical information in the RF signal.