Differential-input amplifier circuit

A differential amplifier as set forth in any of the preceding claims wherein said common-mode feedback means includes, in addition to said third and fourth transistors operating as third-electrode followers responsive to the common-mode voltage component of the signals at said first and second nodes, the following:

• a further transistor of said first conductivity type having the ends of its principal current conduction path defined by respective first and second electrodes thereof, and having a responsive third electrode for controlling the conduction of its principal conduction path according to the potential between its first and third electrodes;
• and
• means connecting said further transistor as a potential follower including
• means for connecting the second electrode of said further transistor to said second operating supply voltage,
• means for connecting the third electrode of said further transistor to said interconnection between the first electrodes of said third and fourth transistors, and
• means for connecting the first electrode of said further transistor for supplying said control signal.

An amplifier circuit including:

• first and second supply terminals for receiving operating voltage therebetween;
• first and second transistors of like conductivity type to each other, each having base and emitter and collector electrodes;
• third and fourth field-effect transistors of conductivity type complementary to that of said first and second transistors, each having gate and source and drain electrodes;
• means for connecting said first and second transistors in first long-tailed-pair configuration including means for applying input signals to their respective base electrodes, and an interconnection between their respective emitter electrodes for receiving a first tail current;
• means for connecting said third and fourth field-effect transistors in second long-tailed-pair configuration including means for connecting the respective collector electrodes of said first and second transistors to the respective gate electrodes of said third and fourth transistors, and an interconnection between the respective source electrodes of said third and fourth transistors for receiving a second tail current;
• first current conductive means connecting the respective drain electrodes of said third and fourth transistors to said second supply terminal;
• the improvement comprising:
• first current mirror amplifying means having at least a first output connection, which first output connection supplies said first tail current to said first long-tailed pair, having an input connection for receiving a first control current for proportionately adjusting its output currents, and having a common connection to said second supply terminal;
• constant current generator means having at least first and second output connections, which first and second output connections respectively connect to the respective collector electrodes of said first and second transistors for supplying their respective collector current demands, having an input connection for receiving a control voltage for proportionately adjusting its output currents, and having a common connection to said first supply terminal;
• second current mirror amplifying means having at least a first output connection, which first output connection supplies said second tail current to said second long-tailed pair, having an input connection for receiving a second control current for proportionately adjusting its output currents, and having a common connection to said first supply terminal;
• common-mode feedback means for generating said control voltage responsive to the common-mode component of the voltages at the collector electrodes of said first and second transistors, which common-mode feedback means completes degenerative feedback loops for adjusting the respective first and second output currents of said constant current generator means to substantially equal the respective collector electrode current demands of said first and second transistors;
• and
• feed forward means independent of said common-mode feedback means for concurrently adjusting said first and second control currents in response to a further control current.