US 4,381,484 AGranted

Transistor current source

AssigneeMotorola, Inc.

InventorRobert B. Jarrett

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Abstract

A PNP transistor current source for sourcing current to a load connected thereto the magnitude of the sourced current being many times greater than the magnitude of a small constant reference current supplied to the current source. The PNP current source is suitable for being manufactured in monolithic integrated circuit form as the current source is made substantially independent to current amplification factor variations normally associated with typical integrated circuit fabrication processes. The PNP current source comprises a pair of PNP transistors having the respective base and emitters commonly coupled together with the emitter area of the output PNP device being N times greater than the emitter area of the other PNP device and including a feedback loop having a current mirror which is coupled between the collector of the other PNP device and the output of the reference current source, a Darlington amplifier coupled between the output of the reference current source and the commonly connected bases of the two PNP transistors wherein the collector currents of the two PNP transistors are made independent to beta variations of each devices.

Claims17

Dependent claims

A current source, comprising:

a pair of transistors each having an emitter, a collector and a base, the base and emitter of each of said pair of transistors being commonly coupled to each other respectively and coupled to a first terminal at which is supplied a first operating potential, said collector of the first one of said transistors being coupled to an output of the current source, said emitter of said first transistor having an area N times greater than the area of said emitter of said second transistor;
amplifying circuit means having an output coupled to said bases of said pair of transistors and an input including an input and an output transistor coupled respectively to said input and output of said amplifying circuit means and resistive means coupled between said output transistor and a second terminal at which is supplied a ground reference potential such that a system, low frequency dominant pole is formed at said input of said amplifying means;
current source means for supplying a constant reference current at an output, said output being coupled to said input of said amplifying means;
current mirror means having first and second inputs coupled respectively to said collector to said second transistor and said current source means;
and
said current mirror means and said amplifying means providing a feedback loop for causing the current sourced from said collector of said first transistor to be N times greater than the current sourced from said collector of said second transistor substantially independent of the beta amplification factor of said first and second transistors.

3 more elements

A current source for sourcing a current to a load connected thereto, comprising:

a first transistor of first conductivity type having an emitter, base and collector, said collector being coupled to an output of the current source, said emitter being coupled to a first terminal at which is supplied a first source of operating potential;
a second transistor of said first conductivity type having an emitter, base and collector, said base being coupled to said base of said first transistor, said emitter being coupled to said emitter of said first transistor, the emitter area of said first transistor being N times greater than the emitter area of said second transistors;
feedback means coupled between said bases of said first and second transistors and said collector of said second transistor for causing said collector current of said first transistor to be N times the magnitude of the collector current flowing from said second transistor and which is substantially independent to variations of the current amplification factor of said first and second transistors;
and
said feedback means including reference current source means for supplying a constant reference current at an output thereof;
current mirror means coupled between said collector of said second transistor and said output of said reference current source;
and
amplifier means coupled between said base of said first transistor and said output of said reference current source means including an output transistor and a resistor coupled between said base of said first transistor and a terminal at which is supplied ground reference potential wherein the closed loop gain of said amplifier means is restricted.

5 more elements

A monolithic integrated current source, comprising:

a first transistor of first conductivity type having an emitter, collector and base, said emitter being coupled to a first terminal for receiving a first source of operating potential, said base being coupled to said first terminal, said collector being coupled to an output of the current source;
a second transistor of said first conductivity type having an emitter, collector and base, said emitter being coupled to said first terminal, said base being coupled to said base of said first transistor;
reference current source means for supplying a substantially contant reference current at an output thereof;
amplifier means coupled between said output of said current reference source means and said base electrode of said first transistor;
current mirror means coupled between said output of said current reference source means and said collector of said second transistor;
and
said amplifier means including a third transistor of a second conductivity type having an emitter, collector and base, said base being coupled to said output of said reference current source means, said collector being coupled to said base of said first transistor, a fourth transistor of said second conductivity type having an emitter, collector, and base, said base being coupled to said emitter of said third transistor, said collector being coupled to said collector of said third transistor, and a first resistor coupled between said emitter of said fourth transistor and a second terminal at which is supplied a reference potential.

4 more elements

Dependencies are inferred from the claim text.