Low Impedance Receiver Frequency Calibration via Impedance Switching
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Solution Overview
Problem
Conventional NMR transceivers with low input impedance receivers face challenges in accurately measuring the resonance frequency of the antenna due to parasitic loading, which affects the signal-to-noise ratio (SNR) and requires correction factors that vary with temperature and parasitic changes, making direct measurement difficult.
Innovation Solution
A system and method that includes a calibration mode where the low input impedance receiver is switched to a high impedance state to directly measure the resonance frequency of the antenna, allowing for real-time determination of the optimum receive frequency considering parasitics and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low input impedance receiver is used, then the signal-to-noise ratio is improved and ultra fast inter echo time is achieved, but the resonance frequency measurement becomes difficult due to parasitic loading
Solution Approach 1:
The receiver impedance is made dynamically switchable between low impedance state during receive mode (for high SNR) and high impedance state during calibration mode (for accurate resonance frequency measurement). This dynamic switching resolves the contradiction by allowing the system to optimize for different functions at different times.
Solution Approach 2:
The operating cycle is segmented into distinct receive mode and calibration mode phases. During receive mode, the low impedance receiver maximizes signal reception. During calibration mode, the high impedance state enables accurate resonance frequency measurement without parasitic loading interference.
2Speed
If a low input impedance receiver is used, then ultra fast inter echo time is achieved, but the frequency response is flattened making resonance frequency determination difficult
Solution Approach 1:
The receiver impedance is dynamically adjusted based on the operational phase. During receive operations, low impedance enables fast inter echo time. During calibration, high impedance restores the frequency response shape for accurate resonance frequency detection.
Solution Approach 2:
A calibration mode is performed before receive operations to determine the resonance frequency. The high impedance state during calibration allows the system to pre-characterize the antenna's resonance properties without the distorting effect of low impedance loading.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and real-time determination of the resonance frequency, improving the signal-to-noise ratio by decoupling the measurement from the receiver's input impedance, thus enhancing the noise performance of the transceiver.
Implementation Method 1
an antenna that is used to transmit and receive radio frequency (RF) signals
Implementation Method 2
The receive circuit typically amplifies the received signal from the antenna for further processing
Implementation Method 3
an NMR transceiver may have a low input impedance pre-amplifier. Thus, a receiving amplifier with a low input impedance can assist in providing an ultra fast inter echo time (Te) between transmitted excitation pulses and received echo signals
Implementation Method 4
Determining the resonance frequency of the antenna is important since the source antenna resonance frequency is often the frequency at which the best noise performance of a transceiver or transceiver system is achieved
Data Source
AI summary
A circuit, system and method for measuring the optimal frequency of transmission and reception for achieving the best possible signal-to-noise ratio (SNR) in low impedance receive systems are provided. In one embodiment, the circuit includes: (1) an antenna that transmits and receives radio-frequency (RF) signals, (2) a receive circuit that is connected to the antenna during a receive mode and a calibration mode, wherein the receive circuit includes an amplifier having a low input impedance, and (3) an impedance switching circuit that places the amplifier in a high input impedance state during the calibration mode.