**5. Discussion**

The IF3602 LNA has better noise characteristics than the current TEM common LT1028 LNA, and its noise reduces to 0.60nV/√Hz at 10 kHz. By comparing the IF3602 LNA TEM receiver and the LT1028 LNA TEM receiver, the observed signal of the receiver with the IF3602 LNA has a significant improvement in effective data length and data quality. The detection depth is increased to 1.6 times that of the former LT1028 system. However, we hold that there are still the following problems, which limit its application and use effect.

Due to the limitations of the JFET device manufacture, the parameters between the devices are quite different, which requires strict pairing before use. Even if the IF3602 used in the experiment has been paired, there are still differences in the internal JFET. The symmetry of the circuit is not as good as that of the ideal differential circuit. The ignored current source also introduces circuit noise. Although the IF3602 has a pair of paired JFETs built-in, its high cost and its inside JFETs parameter difference limit the application of low-noise JFETs.

However, we hold that the above problems can be ameliorated by the following improvements. Before the circuit is manufactured, it is recommended to use a graphic instrument to test the JFET parameter curve and try to select a JFET with similar parameters. If the test conditions are not available, i.e., the parameter characteristic curve cannot be tested, first, a simple circuit can be designed about the minimum noise static operating point in the datasheet, then measure the actual static operating point of each JFET, and select a JFET with good consistency. This can effectively reduce the introduction of common-mode circuit noise caused by JFET parameter difference. Matching can effectively reduce the

demand for JFETs such as the IF3602 that have been matched by manufacturers and can effectively reduce the cost of JFET LNA circuits.
