Pure Class A Preamplifier

It is a differential input circuit composed of field effect transistors . The noise of field effect transistors is much lower than that of transistors
. Theoretical analysis shows that the noise of field effect transistors is about 0-5~1.5nV/
thirty turns, and does not increase with the increase of JD. Therefore, a larger dynamic
range of the circuit can be obtained by increasing its operating current. On the other hand, from the analysis of the noise generated by multi-stage amplifiers, the size of the first-stage noise is
the main source of noise in the entire amplifier. Therefore, using a low-noise input stage is the best choice for obtaining a low-noise amplifier.