Basic amplifier circuit of field effect transistor (a)

Field effect transistors have the advantages of high input impedance, small noise coefficient, good anti-intermodulation and mutual interference performance, etc., and are
increasingly used in electronic circuits. Like transistor amplifiers, field effect tube amplifiers can also be configured as common source (equivalent to common
emitter) amplifiers, common gate (equivalent to common base) amplifiers and common drain (equivalent to common collector) amplifiers. And it can also form a common
source common source amplifier, a common source common gate amplifier and a common source common drain amplifier and other composite circuit forms. As shown in Figure 8-50,
the characteristics of the field effect tube amplifier corresponding to the transistor amplifier are also the same as those of the corresponding transistor amplifier. The transistor circuit is similar to 6.
    It should be pointed out that in the field effect tube amplifier, because
    the gate input resistance of the field effect tube is very high, when the front and rear stage
circuits are cascaded, the influence of the rear stage circuit on the front stage can basically be ignored. This simplifies the design and debugging work. However
, due to its high output A impedance, the influence of distributed capacitance, interelectrode capacitance and Miller effect capacitance is more serious than in transistor circuits
. Therefore, neutralization circuits and common source and common gate are still needed in high frequency circuits. circuit, common source and common drain circuit, etc.
to improve the stability and frequency characteristics of the amplifier.
    In low-frequency amplifier circuits, due to the high input impedance of field effect transistors , noise signals such as hum are easily induced, so
more attention should be paid to process issues such as shielding.