Current scaling apparatus

• US 4,055,774 A
• Filed: 05/27/1976
• Issued: 10/25/1977
• Est. Priority Date: 09/26/1975
• Status: Expired due to Term

• Current Assignee: RCA Corporation (General Electric Company)
• Original Assignee: RCA Corporation (General Electric Company)
• Inventors: Ahmed, Adel Abdel Aziz
• Primary Examiner(s): Miller, Jr., Stanley D.
• Assistant Examiner(s): Davies, B. P.
• Application Number:
  US05/690,719
• Time in Patent Office: 516 Days
• Field of Search: 307/296, 307/397, 307/310, 307/235 R, 307/229, 323/19, 323/22 T, 330/23, 330/40, 330/22, 340/347 AD
• US Class Current: 327/538
• CPC Class Codes: G05F 3/265 using bipolar transistors only
• CPC Class Codes: H03F 3/343 with semiconductor devices only

Abstract

The difference between the base potentials of a pair of transistors, which are interconnected at their emitter electrodes and operated with different densities of current flow through their base-emitter junctions, is scaled up by a fixed ratio and applied between the base electrodes of another pair of transistors with interconnected emitter electrodes to cause their collector currents to flow in a desired ratio.

Claims

1. A current scaling apparatus comprising, in combination:

first and second and third and fourth transistors, each having base and emitter electrodes and a base-emitter junction therebetween and having a collector electrode, said first and said second transistors being of the same conductivity type as each other and having interconnected emitter electrodes, said third and said fourth transistors being of the same conductivity type as each other and having interconnected emitter electrodes;

means operating said third and said fourth transistors with different densities of current flow through their respective base-emitter junctions for defining a difference between their respective base potentials;

means for scaling up the difference between the base potentials of said third and said fourth transistors by a fixed ratio; and

means applying the scaled up difference potential between the base electrodes of said first and said second transistors for determining the ratio between their respective collector currents.

2. A current scaling apparatus as set forth in claim 1 wherein said means for scaling up the difference between the base potentials of said first and said second transistors comprises direct current impedance means across which said difference potential between said base potentials is applied thereby to establish a flow of current through said impedance means, a series circuit, including said impedance means and another direct current impedance means through which said current flows, and a pair of terminals connected to points along said series circuit for producing said scaled up difference between potentials.

3. A current scaling apparatus for responding to an input current to supply an output current proportional to its said input current, said current scaling apparatus comprising:

first and second and third and fourth junction transistors, all made of the same basic semiconductive material and operated at substantially the same absolute temperature T, each having base and emitter electrodes with a base-emitter junction therebetween and each having a collector electrode, said first and said second transistors being of the same conductivity type as each other and said third and said fourth transistors being of the same conductivity type as each other;

an input terminal for receiving said input current, galvanically coupled to the collector electrode of said first transistor;

an output terminal for delivering said output current to which the collector electrode of said second transistor is galvanically coupled;

a common terminal for return of said input and output currents, to which the emitter electrodes of said first and said second transistors are directly connected without substantial intervening impedance;

means applying direct-coupled degenerative collector-to-base to said first transistor for regulating its base potential to condition it to accept as collector current essentially the entire input current as received at said input terminal and galvanically coupled to its collector electrode;

a potential divider having an input port connected between the base electrodes of said first and said second transistors and having an output port connected between the base electrodes of said third and said fourth transistors;

first direct current conductive means, linking said common terminal and a first circuit node, to which node the emitter electrodes of said third and said fourth transistors are directly connected without substantial intervening impedance;

differential combining means for differentially combining the collector currents of said third and said fourth transistors to develop an error signal when the potential between the base electrodes of said thid and said fourth transistors departs from a predetermined value; and

means responsive to said error signal for applying a current proportional to said error signal, applied at the base electrode of said second transistor in a sense to degenerate said error signal.

4. A current scaling apparatus as set forth in claim 3 wherein the area of the base-emitter junction of said fourth transistor is m times as large as the area of the base-emitter junction of said third transistor;

said differential combining means is a current amplifier having an input connection to which the collector electrode of said fourth transistor is connected, having an output connection connected to a second circuit node to which the collector electrode of said third transistor is also connected and at which said error signal is provided, and exhibiting a current gain of -n between its said input and output connections; and

the product of m times n is chosen larger than unity, thereby tending to cause said output current to be smaller than said input current by a predetermined ratio substantially independent of the values of said input and output currents over an operating range.

5. A current scaling apparatus as set forth in claim 4 wherein said means responsive to said error signal for applying a current includes:

a fifth transistor being of the same conductivity type as said first and said second transistors, having a base electrode to which said second circuit node is direct coupled, having an emitter electrode referred in potential to said common terminal, and having a collector electrode direct coupled to the base electrode of said second transistor.

6. A current scaling apparatus as claimed in claim 4 wherein said means applying direct-coupled degenerative feedback to said first transistor comprises a further transistor connected as a potential follower with input connection and output connection at the collector and base electrodes, respectively, of said first transistor.

7. A current scaling apparatus as set forth in claim 3 wherein the area of the base-emitter junction of said fourth transistor is m times as large as the area of the base-emitter junction of said third transistor;

said differential combining means is a current amplifier having an input connection to which the collector electrode of said third transistor is connected, having an output connection connected to a second circuit node to which the collector electrode of said fourth transistor is also connected and at which said error signal is provided, and exhibiting current gain -1/n between its said input and output connections; and

the product of m times n is chosen larger than unity, thereby tending to cause said output current to be smaller than said input current by a predetermined ratio substantially independent of the values of said input and output currents over an operating range.

8. A current scaling apparatus as set forth in claim 7 wherein said means responsive to said error signal for applying a current includes:

fifth and sixth transistors respectively of opposite conductivity type to and of the same conductivity type as the conductivity type of said first and said second transistors;

means connecting said fifth transistors in common-emitter amplifier configuration, including a direct coupling of said second circuit node to the base electrode of said fifth transistor;

means connecting said sixth transistor in common-emitter amplifier configuration, including a direct coupling of its collector electrode to the base electrode of said second transistor; and

means connecting the aforeclaimed common-emitter amplifier configuration is cascade, including a direct coupling of the collector electrode of said fifth transistor to the base electrode of said sixth transistor.

9. A current scaling apparatus as set forth in claim 7 wherein said means responsive to said error signal for applying a current includes:

a fifth transistor being of the same conductivity type as said first and said second transistors, having a base electrode to which said second circuit node is direct coupled, having an emitter electrode direct coupled to the base electrode of said second transistor, and having a collector electrode biased to condition said fifth transistor for emitter-follower operation.

10. A current scaling apparatus as claimed in claim 7 wherein said means applying direct-coupled degenerative feedback to said first transistor comprises a fourth transistor connected as a potential follower with input connection and output connection at the collector and base electrodes, respectively, of said first transistor.

11. A current scaling apparatus as set forth in claim 3 wherein the area of the base-emitter junction of said fourth transistor is m times as large as the area of the base-emitter junction of said third transistor;

said differential combining means is a current amplifier having an input connection to which the collector electrode of said fourth transistor is connected, having an output connection connected to a second circuit node to which the collector electrode of said third transistor is also connected and at which said error signal is provided, and exhibiting a current gain of -n between its said input and output connections; and

the product of m times n is chosen smaller than unity, thereby tending to cause said output current to be larger than said input current by a predetermined ratio substantially independent of the values of said input and output currents over an operating range.

12. A current scaling apparatus as set forth in claim 11 wherein said means responsive to said error signal for applying a current includes:

a fifth transistor being of the same conductivity type as said first and said second transistor, having a base electrode to which said second circuit node is direct coupled, having an emitter electrode referred in potential to said common terminal, and having a collector electrode direct coupled to the base electrode of said second transistor, together with

means for applying a current to the base electrode of said second transistor to forward bias its base-emitter junction.

13. A current scaling apparatus as set forth in claim 11 wherein said means responsive to said error signal for applying a current includes:

a fifth transistor being of the same conductivity type as said first and said second transistors, having a base electrode to which said second circuit node is direct coupled, having an emitter electrode biased to operate said fifth transistor in common-emitter amplifier configuration, and having a collector electrode connected to the base electrode of said second transistor; and

means for applying a flow of current to the base electrode of said second transistor opposing the flow of the collector current of said fifth transistor to the base electrode of said fifth transistor.

14. A current scaling apparatus as set forth in claim 3 wherein the area of the base-emitter junction of said fourth transistor is m times as large as the area of the base-emitter junction of said third transistor;

said differential combining means is a current amplifier having an input connection to which the collector electrode of said third transistor is connected, having an output connection connected to a second circuit node to which the collector electrode of said fourth transistor is also connected and at which said error signal is provided, and exhibiting a current gain of -1/n between its said input and output connections; and

the product of m times n is chosen smaller than unity, thereby tending to cause said output current to be larger than said input current by a predetermined ratio substantially independent of the values of said input and output currents over an operating range.

15. A current scaling apparatus as set forth in claim 14 wherein said means responsive to said error signal for applying a current includes:

fifth and sixth transistors, respectively of the same conductivity type as and of opposite conductivity type to the conductivity type of said first and said second transistors, and

means for connecting each of said fifth and sixth transistors in common emitter amplifier configuration wherein

said second circuit node is direct coupled to the base electrode of said fifth transistor, the collector electrode of said fifth transistor is direct coupled to the base electrode of said sixth transistor and the collector electrode of said sixth transistor is direct coupled to the base electrode of said second transistor.

16. A current scaling apparatus as set forth in claim 14 wherein said means responsive to said error signal for applying a current includes:

a fifth transistor being of the same conductivity type as said first and said second transistors, having a base electrode to which said second circuit node is direct coupled, having an emitter electrode direct coupled to the base electrode of said second transistor, and having a collector electrode biased to condition said fifth transistor for emitter-follower operation.

17. A current scaling apparatus as set forth in claim 3 wherein said potential divider comprises a first resistance across which its said output port appears and at least one further resistance across which and said first resistance its said input port appears.

18. A current scaling apparatus as set forth in claim 3 wherein said first direct current conductive means comprises a source of direct current.

19. A current scaling apparatus as claimed in claim 3 wherein said first direct current conductive means consists of a direct connection of said first circuit node to said common terminal.

20. Apparatus comprising:

first and second transistors of the same conductivity type, each having base and emitter electrodes with a base-emitter junction therebetween, having a collector electrode, and being operated at substantially the same temperature T;

means for applying a current to the interconnection of the emitter electrodes of said first and said second transistors which is of a polarity tending to forward bias their respective base-emitter junctions and thus cause respective collector current flows through their respective collector electrodes;

means for differentially combining in predetermined proportion the collector currents of said first and said second transistors to obtain an error signal;

a number, at least one, of further semiconductor junctions operated at substantially the temperature T;

a plurality of resistive means with resistances in fixed proportion to each other connected in series connection with said number of further semiconductor junctions;

means for applying a current proportional to said error signal to said series connection in a sense to forward bias each of said number of further semiconductor junctions, thereby to develop an output potential across said series connection characteristic of a multiple of the offset potential across a semiconductor junction operated at higher current density than each said further semiconductor junction; and

means applying a portion of said output potential, as appears across one of said resistive means, between the base electrodes of said first and said second transistors in a sense for completing a degenerative feedback loop for regulating this potential to a predictable value.

21. Apparatus as set forth in claim 20 wherein said first and said second transistors are physically proportioned so the second transistor would have m times the collector current of said first transistor were they to have similar emitter-to-base potentials;

wherein said means for differentially combining their collector currents in predetermined proportion comprises a current amplifier having an input terminal to which the collector electrode of said first transistor is connected, having an output terminal to which the collector electrode of said second transistor is connected and at which said error signal appears, and providing a current gain of minus unity divided by n between its input and output terminals; and

wherein said means for applying a current proportional to said error signal comprises a third transistor, being of the same conductivity type as said first and said second transistor, being operated as a common-collector amplifier, having a base electrode to which said error signal is applied by direct coupling, and having an emitter electrode direct coupled to the end of said series connection more remote from the base electrode of said first transistor than from the base electrode of said second transistor, m and n being positive numbers, the product of which exceeds unity and said predictable value of potential between the base electrodes of said first and said second transistors being equal to (kT/p) ln (mn), where k is Boltzmann'"'"'s constant and q is the charge on an electron.

22. Apparatus as set forth in claim 20 wherein said first and said second transistors are physically proportioned so the second transistor would have m times the collector current of said first transistor were they to have similar emitter-to-base potentials;

wherein said means for differentially combining their collector currents in predetermined proportion comprises a current amplifier having an input terminal to which the collector electrode of said second transistor is connected, having an output terminal to which the collector electrode of said first transistor is connected and at which said error signal appears, and providing a current gain of n between its input and output terminals; and

wherein said means for applying a current proportional to said error signal comprises a third transistor, being of complementary conductivity type to that of said first and said second transistors, being operated as a common-emitter amplifier, having a base electrode to which said error signal is applied by direct coupling, and having a collector electrode direct coupled to the end of said series connection more remote from the base electrode of said first transistor than from the base electrode of said second transistor, m and n being positive numbers the product of which is less than unity and said predictable value of potential between the base electrode of said first and said second transistors being equal to (kT/q) ln (mn), where k is Boltzmann'"'"'s constant and q is the charge on an electron.

23. Apparatus as set forth in claim 20 used in combination with a third transistor operated at substantially said temperature T for determining current flowing through a collector electrode of said third transistor, said third transistor having base and emitter electrodes respectively connected to opposite ends of said series connection and having a base-emitter junction between its base and emitter electrodes.

24. Apparatus comprising:

a first terminal connected to a point of reference potential, a second terminal, and a third terminal;

first and second transistors of the same conductivity type, each having base and emitter electrodes with a base-emitter junction therebetween, having a collector electrode, and being operated at substantially the same temperature T;

means for applying a current to the interconnection of the emitter electrodes of said first and said second transistors which is of a polarity tending to forward bias their respective base-emitter junctions and thus cause respective collector current flows through their respective collector electrodes;

means for differentially combining in predetermined proportion the collector currents of said first and said second transistors to obtain an error signal;

a number, at least one, of further semiconductor junctions operated at substantially the temperature T arranged in a current path between said first and said second terminals with no substantial intervening impedance;

an input current source connected between said first and said second terminals for applying an input current of a polarity to forward bias each said further semiconductor junction connected therein, responsive to which an offset potential appears between said first and said second terminals;

resistance means connected between said second terminal and said third terminal;

means for applying a current proportional to said error signal to said series connection, responsive to which a potential appears between said second and said third terminals;

means applying the potential appearing across a portion of said resistance means between the base electrodes of said first and second transistors, thereby completing a degenerative feedback loop for regulating this potential to a predictable value; and

means connected between said first and said third terminals for utilizing the potential appearing therebetween.

25. Apparatus as set forth in claim 24 wherein said first and said second transistors are physically proportioned so the second transistor would have m times the collector current of said first transistor were they to have similar emitter-to-base potentials;

and wherein said means for differentially combining their collector currents in predetermined proportion comprises a current amplifier having an input terminal to which the collector electrode of said second transistor is connected, having an output terminal to which the collector electrode of said first transistor is connected and at which said error signal appears, and providing a current gain of minus one divided by n between its input and output terminals, m and n being positive numbers and said predictable value of potential between the base electrodes of said first and said second transistors being equal to (kT/q) ln (mn), where k is Boltzmann'"'"'s constant and q is the charge on an electron.

26. Apparatus as set forth in claim 24 wherein said first and said second transistors are physically proportioned so the second transistor would have m times the collector current of said first transistor were they to have similar emitter-to-base potentials;

and wherein said means for differentially combining their collector currents in predetermined proportion comprises a current amplifier having an input terminal to which the collector electrode of said first transistor is connected, having an output terminal to which the collector electrode of said second transistor is connected and at which said error signal appears, and providing a current gain of n between its input and output terminals, m and n being positive numbers and said predictable value of potential between the base electrodes of said first and said second transistors being equal to (kT/q) ln (mn), where k is Boltzmann'"'"'s constant and q is the charge on an electron.

27. Apparatus as set forth in claim 24 wherein said means connected between said first and said third terminals for utilizing the potential appearing therebetween includes a third transistor being operated at substantially said temperature T, having base and emitter electrodes connected to separate ones of said first and said third terminals, and having a collector electrode for conducting an output current proportionally responsive to said input current.