Current mirror amplifier

Abstract

A current mirror amplifier in which the potentials appearing across the principal conduction paths of its master and slave transistors are maintained substantially the same. This is done by a differential-input, single-ended output amplifier, which is connected as a non-inverting amplifier in the direct-coupled feedback connection that conditions the master transistor to conduct applied input current via its principal conduction path.

What is claimed is: 
     
       1. A current mirror amplifier comprising: an input terminal;   an output terminal;   a common terminal;   first and second transistors of a first conductivity type, having respective input electrodes, having respective common electrodes connected to said common terminal, and having respective output electrodes connected respectively to said input terminal and to said output terminal; and   a differential-input single-ended-output amplifier having non-inverting and inverting input connections respectively at said input terminal and at said output terminal and having an output connection connected to an interconnection between the input electrodes of said first and said second transistors, said amplifier applying a signal to said interconnection having positive polarity when the potential at said non-inverting input connection is positive relative to the potential at said inverting input connection and having negative polarity when the potential at said non-inverting input connection is negative relative to the potential at said inverting input connection.   
     
     
       2. A current .Iadd.mirror .Iaddend.amplifier as set forth in claim 1 wherein said differential-input single-ended-output amplifier includes: third and fourth transistors of a second conductivity type complementary to said first conductivity type, having respective input electrodes to which said input terminal and said output terminal are respectively connected, having respective common electrodes, and having respective output electrodes;   a subsidiary current mirror amplifier having an input connection to which the output electrode of said third transistor connects, having an output connection to which the output electrode of said fourth transistor is connected, and having a common connection;   means for applying quiescent current between the common terminal of said subsidiary current mirror amplifier and an interconnection between the common electrodes of said third and fourth transistors; and   means connecting the output connection of said subsidiary current mirror amplifier to said interconnection between the input electrodes of said first and said second transistors.   
     
     
       3. A current mirror amplifier as set forth in claim 2 wherein the common connection of said subsidiary current mirror amplifier is at said common terminal. .Iadd. 4. A circuit for maintaining the potential at a first node substantially equal to the potential at a second node, said circuit comprising: first and second supply terminals for receiving an operating potential therebetween;   current conductive impedance means connecting said first node to said first supply terminal;   first, second and third transistors, each having first and second electrodes and a controlled conductivity principal current conduction path therebetween and having a third or control electrode, the conductivity of its principal current conduction path being controlled responsive to potential appearing between its first and third electrodes, said first and second transistors being of the same conductivity type as each other,   means connecting said first and second transistors in long-tailed-pair configuration including an interconnection of their respective first electrodes, means for applying current to said interconnection of said respective first electrodes, a connection of the third electrode of said first transistor to said second node, and a connection of the third electrode of said second transistor to said first node,   a third node to which the second electrode of said first transistor connects;   means connecting said third transistor in common-first-electrode amplifier configuration including   means connecting the first electrode of said third transistor to one of said first and second supply terminals,   means direct coupling said third node to the third electrode of said third transistor, and including   a connection of the second electrode of said third transistor to said first node; and   current amplifier means having an input connection from the second electrode of said second transistor and having an output connection to said third node for differentially combining currents from the second electrodes of said first and second transistors to a single-ended current.   
     
     
        .Iaddend. .Iadd. 5.  A combination as set forth in claim 4 wherein said first and second transistors are so proportioned respective to each other as to have the conductivities of their respective principal current conduction paths be in 1 :G ratio with each other for similar first-to-third-electrode potentials and wherein the current gain of said current amplifier is -G, G being a positive number. .Iaddend. .Iadd. 6. A combination as set forth in claim 4 wherein said third transistor is of opposite conductivity type from that of said first and second transistor, and wherein said means connecting the first electrode of said third transistor to one of said first and second supply terminals consists of means connecting the first electrode of said third transistor to said first supply terminal.