核磁共振测井仪低噪声模拟接收电路设计

Low Noise Analog Receiver Design for NMR Logging Tool

设计了一种用于核磁共振测井仪的低噪声模拟接收电路。第1级放大为自主构建的仪器用放大器,其增益为52dB,选用最佳源电阻与天线谐振阻抗相近的超低噪声宽带运放LMH6626保证电路的低噪声性能。对第1级放大器的噪声性能进行了理论分析,其噪声系数为1.45。实验测试结果表明,电路最大增益为112dB,频率范围为400kHz～1MHz,可对核磁共振信号进行低噪声放大,并已成功应用于核磁共振测井仪实验室样机中。

We present a novel low noise analog receiver for nuclear magnetic resonance （NMR） logging tool. The first stage is home-built tool amplifier, and the designed gain is 52 dB. The first stage uses ultra low noise wideband operational amplifier LMH6626 which its optimum source resistance is very close to the antenna impedance to guarantee the optimum noise performance. The noise performance of first stage was analyzed, and the calculated noise figure is 1.45. Test results show that the maximal gain of analog receiver is 112 dB and the frequency bandwidth is from 400 kHz to 1 MHz. The analog receiver has been used for laboratory prototype NMR logging tool successfully and can amplify NMR signal with low noise performance.