磁共振线圈低噪声前置放大器的噪声系数测量研究

Study on measurement of MRI coil low noise preamplifier noise figure

目的：根据噪声系数的测量原理,研究一种测量磁共振线圈低噪声前置放大器噪声系数的方法。方法：使用AV3981噪声系数测量仪的1.0测试模式,设置测量频率范围为100~160 MHz,间隔为2 MHz。应用超噪比为14.09 d B的噪声源进行矫正,接入低噪声前置放大器进行测量,并使用Excel表格软件作数据处理,画出原数据曲线和多项式拟合曲线。结果：增益的拟合曲线呈现两边低中间高特性,在124~130 MHz间大于22 d B,噪声系数拟合曲线在124~130 MHz之间相对平缓,均在1.77 d B以下。结论：该测量方法能满足对低噪声前置放大器的测量需要,为以后进一步研制噪声系数更低的低噪声前置放大器提供有效的测量手段。

Objective To study a method for measuring MRI coil low noise preamplifier noise figure. Methods AV3981 noise figure meter was set as 1.0 test mode, with frequency measurement range between 100 and 160 MHz and the intervals of 2 MHz. The noise source with the excess noise ratio of 14.09 d B was used for correction, and then the low noise preamplifier was measured. Excel was applied to data processing to obtain raw data curve and polynomial fitting curve. Results The gain fitting showed low values at both sides and high values in the middle, with the value more than22 d B within the range from 124 to 130 MHz; noise figure fitting curve showed a relatively flattened trend within the range from 124 to 130 MHz, with the values less than 1.77 d B. Conclusion The method can be used for the measurement of MRI coil low noise preamplifier noise figure, and may be a measuring tool for other low noise preamplifier with lower noise figure than before.