Transistor Dual Differential Input Stage

A transistor double differential circuit is used as the input stage, as shown in Figure 1-37. Analysis of this circuit shows that since a
pair of differential circuits with different polarities are connected, their base currents are opposite. Therefore, there is almost no current flowing through the bias resistors on both sides,
so the resistors on both sides can be of any value. The difficulty is that the parameters of the left and right, upper and lower tubes must be strictly consistent.
    Use field effect tube differential (or double differential) circuit for A-level output. For IX: power amplifier, using field effect transistor (generally junction type
) differential circuit as the input stage is the most convenient, reliable and stable circuit form. The general OCL circuit cancels CF and becomes a DC
power amplifier, and its circuit structure can remain unchanged. . Because the field effect transistor is a voltage-controlled component with a very high input resistance and basically
draws no current, the bias resistors of the two differential tubes can be set to any value without changing their static bias voltage and drain current .