Class-S MRI RF Transmitter With PARR for High-SNR Modulation
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Solution Overview
Problem
Conventional Class-S RF transmitters for MRI scanners face inefficiencies due to high peak to average amplitude variation in input signals, leading to poor sampling of low amplitude values and decreased signal-to-noise ratio (SNR), which affects the overall signal linearity and efficiency of the Delta Sigma Modulation (DSM) process.
Innovation Solution
The implementation of a Peak to Average Ratio Reduction (PARR) block in the Class-S RF transmitter reduces the peak to average amplitude variation of the analog input signal, allowing efficient sampling at all amplitude values and enhancing the performance of the DSM block by generating a digitally modulated signal with high SNR, which is then amplified by a Class-D RF power amplifier using a dynamic supply modulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high sampling frequency is used in Delta Sigma Modulation to achieve high linearity, then signal linearity is improved, but switching frequency increases causing decreased efficiency and requiring wide band RF power amplifier
Solution Approach 1:
The patent applies preliminary action by pre-processing the input signal through peak clipping and averaging operations before it enters the Delta Sigma Modulation block. This preliminary processing reduces the peak-to-average ratio of the signal, allowing the DSM to operate with lower sampling frequencies while maintaining signal fidelity and linearity, thereby avoiding the efficiency losses associated with high-frequency switching
2Measurement precision
If high sampling frequency is used in Delta Sigma Modulation, then signal quality is maintained, but the frequency band requirement of RF power amplifier increases
Solution Approach 1:
By applying peak clipping and averaging operations before Delta Sigma Modulation, the patent reduces the spectral content requirements of the subsequent stages. This preliminary processing ensures that the signal enters the modulator with reduced peak-to-average ratio, allowing for lower sampling frequencies that in turn reduce the bandwidth requirements of the RF power amplifier while preserving essential signal quality
3Extent of automation
If conventional Class-S RF transmitter architecture is used, then digital modulation capability is achieved, but peak to average amplitude variation causes poor sampling of low amplitude values and decreased SNR
Solution Approach 1:
The patent applies preliminary signal processing operations (peak clipping and averaging) before the signal enters the digital modulation and Delta Sigma Modulation stages. This preliminary action reduces the peak-to-average amplitude variation, ensuring that low amplitude values are properly represented and sampled throughout the digital processing chain, thereby maintaining high signal-to-noise ratio while preserving digital modulation capability
Solution Approach 2:
The patent introduces intermediary processing blocks (peak clipper and averager) between the input signal and the Delta Sigma Modulator. These intermediary components modify the signal characteristics to reduce peak-to-average ratio, acting as mediators that prepare the signal for optimal digital processing without losing information or degrading SNR
Data Source
AI summary
An analog input signal (X(n)) is processed by a Peak to Average Ratio Reduction (PARR) block to diminish the difference between peak amplitudes and average amplitudes of the analog input signal (X(n)). After, a distorted signal (h(n)) having low peak to average amplitude ratio, generated at the PARR block output, is processed by a delta sigma modulation (DSM) block converts the distorted signal (h(n)) into a digitally modulated distorted signal (h_dsm(n)) with high signal to noise ratio (SNR). Afterwards, the digitally modulated distorted signal (h_dsm(n)) is corrected and amplified by a Class-D RF power amplifier fed by a feeding signal (env(n)) generated from a digital correction signal (z_dsm(n)). As a result, a digitally modulated signal (y(n)) with high signal to noise ratio (SNR) of the analog input signal (X(n)) is generated at the output of the Class-D RF power amplifier.