噪声前置放大器是磁共振射频接收子系统中的重要组件,它的性能优劣直接决定了最终磁共振图像的好坏.目前市场上的低噪声前置放大器大多基于中高场磁共振系统开发,而针对低场磁共振系统的很少;另外,商用低场磁共振系统的低噪声前置放大器价格相对较贵,并且多采用两级放大结构,结构复杂、调试难度大、成本相对较高.在此背景下,针对0.5 T低场磁共振设备利用Keysight公司的先进设计系统(ADS)软件对低噪声前置放大器进行研究设计,采用一级放大结构,探索电路设计与布局对放大器性能的影响.实测结果表明自主设计的低噪声前置放大器在21 MHz共振频率附近噪声系数为0.5 dB左右,增益达到了30 dB,能够满足低场磁共振应用的要求.%Low noise pre-amplifier is an important component in the radiofrequency (RF) receiving subsystem of magnetic resonance systems. The performance of pre-amplifier determines the quality of the final images directly. Currently, low noise pre-amplifiers on the market mostly are designed for high-field magnetic resonance systems. Few such low noise pre-amplifiers were designed specifically for low-field magnetic resonance systems. Moreover, commercially-available low noise pre-amplifiers are relatively expensive, and most of the designs use a complicated two-stage amplification structure. For these reasons, a low noise pre-amplifier with only one-stage amplification structure was developed in this study for 0.5 T low-field magnetic resonance systems using the advanced design system (ADS) software. The circuit design and layout effects were presented. Experimental measurement showed that the noise figure of on-resonance frequency 21 MHz was about 0.5 dB, and a gain of 30 dB was achieved.
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