Constant current source differential amplifier circuit a

Constant current source differential amplifier circuit a

(2) Differential amplifier  with constant current source
    In the differential amplifier with emitter resistor &, if the larger the resistor &, Ua will also increase accordingly, which is inappropriate. In order to make
Ucc lower when V increases, a triode can be used instead of &. This circuit is called a transistor constant current source differential amplifier , as shown in the figure.
    In the figure, , & play the role of voltage divider, providing bias voltage for the base of VT3, making it work in an amplified state. Its working principle: When
the electric potential increases, the voltage I*3Re at both ends of & also increases, but G remains unchanged, forcing U. decreases, thereby reducing the island,
causing the decrease of R, suppressing the rise of R, and keeping the upper 3 unchanged. This is the constant current source function of the transistor VT3. If si remains unchanged, it will be suppressed that si and
ru cannot increase, thereby effectively suppressing zero point drift.