US3517324A - Complementary emitter follower - Google Patents

Complementary emitter follower Download PDF

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US3517324A
US3517324A US699437A US3517324DA US3517324A US 3517324 A US3517324 A US 3517324A US 699437 A US699437 A US 699437A US 3517324D A US3517324D A US 3517324DA US 3517324 A US3517324 A US 3517324A
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transistor
base
emitter follower
emitter
complementary emitter
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US699437A
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David Eric Perlman
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Eastman Kodak Co
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Eastman Kodak Co
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/50—Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5018—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source follower has a controlled source circuit, the controlling signal being derived from the source circuit of the follower
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5021—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source follower has a controlled source circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5027—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source follower has a current mirror output circuit in its source circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5031—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source circuit of the follower being a current source
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5036—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source follower has a resistor in its source circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/50—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F2203/5045—Indexing scheme relating to amplifiers in which input being applied to, or output being derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower the source follower has a level shifter between source and output, e.g. a diode-connected transistor

Definitions

  • the above and other objects of the invention are accomplished by providing a constant current source as the common emitter to ground and base to ground load of a prior art complementary emitter follower.
  • the invention is further accomplished by arranging the constant current source so that its resistances have low values and can be economically fabricated as an integrated circuit.
  • FIG. 1 is a schematic diagram of a prior art complementary emitter follower
  • FIG. 2 is a schematic diagram of a complementary emitter follower according to the invention wherein the constant current source is shown symbolically, and
  • FIG. 3 is a schematic dagram of a complementary emitter follower according to the invention showing all of the discrete components.
  • FIG. 1 there is shown a prior art complementary emitter follower.
  • NPN transistor Q has its base connected to the input I Its collector is connected to a positive supply, whereas its emitter is connected to the base of PNP transistor Q
  • Resistor R is connected from the base of transistor Q to the collector of transistor Q
  • the emitter of transistor Q is connected to a positive supply through resistor R
  • the potential on the base of transistor Q is therefore raised which tends to decrease the conductivity of transistor Q
  • the output Voltage E therefore approaches the supply voltage.
  • the input impedance of the circuit is approximately proportional to the value of resistor R In order to increase the input impedance the value 3,517,324 Patented June 23, 1970 of resistance R may be raised. However, a limit is reached when R no longer passes enough current to drive the base of transistor Q It can therefore be seen that it is desirable to be able to raise the input impedance of the circuit of FIG. 1 and that it would also be desirable to be able to fabricate the amplifier as an integrated circuit.
  • FIG. 2 shows the invention in its broadest aspects.
  • Resistor R of FIG. 1 has been replaced by constant current generator C Since a constant current generator has a theoretical infinite impedance, a very high input impedance is obtained.
  • FIG. 3 shows a circuit diagram of a complementary emitter follower using a constant current generator C wherein the resistance values are low enough to be fabricated as integrated circuits.
  • Transistor Q acts as a diode and serves to keep the voltage at the base of transistor Q approximately constant.
  • the conductance of NPN tranisstor Q of course, is dependent upon its base to emitter drop. This base to emitter drop is dependent upon the current passing through resistor R As in FIG. 1 when the input voltage on transistor Q rises, the output voltage E rises with it.
  • the input current is approximately one nanoampere
  • the constant current through NPN transistor Q is approximately 340 nanoamperes.
  • the current through PNP transistor Q is approximately 22 microamperes.
  • the value of R is approximately 10KB which is economical to fabricate in an integrated circuit.
  • a complementary emitter follower comprising:
  • a second transistor having base, emitter, and collector electrodes, the base of said second transistor being electrically coupled to the emitter of said first transistor, said output terminal being electrically coupled to the emitter of said second transistor,
  • a second circuit defining a source of substantially constant current connected directly between the base and collector electrodes of said second transistor, and coupled to said resistance for increasing the voltage drop across said resistance.
  • said second circuit comprises a third transistor having base, collector, and emitter electrodes, the emitter-collector path of said third transistor being electrically coupled across the base-collector path of said second transistor, and further comprising:
  • a fourth transistor having base, emitter, and collector electrodes, said base and collector electrodes being electrically coupled together and to the base of said third transistor.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)

Description

June 23, 1970 0.,5. PERLMAN 3,517,324
COMPLEMENTARY EMITTER FOLLOWER Filed Jan. 22, 1968 E0 FIG] (PRIOR ART) DAVID E. PERLMAN VENT ATTORNEYS United States Patent O 3,517,324 COMPLEMENTARY EMITTER FOLLOWER David Eric Perlman, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Jan. 22, 1968, Ser. No. 699,437 Int. Cl. H03f 3/18 US. Cl. 330-17 3 Claims ABSTRACT OF THE DISCLOSURE A current amplifier has a very high input impedance and is easily fabricated as an integrated circuit. It uses resistors having comparatively low values, and a constant current source for base bias.
BACKGROUND OF THE INVENTION In the prior art it has been very difiicult to design an emitter follower which has a very high input impedance, has good linearity, and uses low values of resistance so that the amplifier can be constructed as an integrated circuit.
SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a complementary emitter follower having a high input impedance, having excellent linearity, and having low values of circuit resistances.
The above and other objects of the invention are accomplished by providing a constant current source as the common emitter to ground and base to ground load of a prior art complementary emitter follower. The invention is further accomplished by arranging the constant current source so that its resistances have low values and can be economically fabricated as an integrated circuit.
BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood from the drawing in which:
FIG. 1 is a schematic diagram of a prior art complementary emitter follower,
FIG. 2 is a schematic diagram of a complementary emitter follower according to the invention wherein the constant current source is shown symbolically, and
FIG. 3 is a schematic dagram of a complementary emitter follower according to the invention showing all of the discrete components.
DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a prior art complementary emitter follower. NPN transistor Q has its base connected to the input I Its collector is connected to a positive supply, whereas its emitter is connected to the base of PNP transistor Q Resistor R is connected from the base of transistor Q to the collector of transistor Q The emitter of transistor Q; is connected to a positive supply through resistor R When the input current I, between the base of transistor Q and a common terminal, shown here as ground goes positive, transistor Q tends to increase its conductivity. The potential on the base of transistor Q, is therefore raised which tends to decrease the conductivity of transistor Q The output Voltage E therefore approaches the supply voltage. Since the base to emitter voltage drop of transistor Q, is approximately the same as the base to emitter voltage drop of transistor Q the input voltage will be almost exactly the same as the output voltage as long as the amplifier is operating unsaturated. The input impedance of the circuit is approximately proportional to the value of resistor R In order to increase the input impedance the value 3,517,324 Patented June 23, 1970 of resistance R may be raised. However, a limit is reached when R no longer passes enough current to drive the base of transistor Q It can therefore be seen that it is desirable to be able to raise the input impedance of the circuit of FIG. 1 and that it would also be desirable to be able to fabricate the amplifier as an integrated circuit.
FIG. 2 shows the invention in its broadest aspects. Resistor R of FIG. 1 has been replaced by constant current generator C Since a constant current generator has a theoretical infinite impedance, a very high input impedance is obtained.
Although the circuit shown in FIG. 2 is exactly what is needed, its actual reduction to practice as an integrated circuit is extremely difficult to attain because constant current generators usually employ very high values of resistance when the current to be generated is very low. As pointed out above, the use of high values of resistances in integrated circuits is quite uneconomical.
FIG. 3 shows a circuit diagram of a complementary emitter follower using a constant current generator C wherein the resistance values are low enough to be fabricated as integrated circuits. Transistor Q acts as a diode and serves to keep the voltage at the base of transistor Q approximately constant. The conductance of NPN tranisstor Q of course, is dependent upon its base to emitter drop. This base to emitter drop is dependent upon the current passing through resistor R As in FIG. 1 when the input voltage on transistor Q rises, the output voltage E rises with it. When the output voltage E rises, the current through transistor Q decreases thus reducing the voltage drop across resistor R thus increasing the conductance of transistor Q and thus tending to keep a constant current through transistor Q The action of the current through transistor Q to control, via its voltage drop across resistor R the conductance of transistor Q constitutes a negative feedback loop. This negative feedback loop helps to provide high input impedance at the base of Q and increases the circuits insensitivity to thermal, supply voltage and transistor gain variations.
In a typical example, the input current is approximately one nanoampere, and the constant current through NPN transistor Q is approximately 340 nanoamperes. The current through PNP transistor Q is approximately 22 microamperes. The value of R is approximately 10KB which is economical to fabricate in an integrated circuit.
It is, of course, apparent that it is not essential to the invention to fabricate the circuit as an integrated circuit. The operation of the invention is the same if discrete components are used.
Although the invention has been described in considerable detail with reference to a certain preferred embodiment thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
I claim:
1. A complementary emitter follower comprising:
(a) an input terminal, an output terminal, and a common terminal,
(b) a first transistor having base, emitter, and collector electrodes, said base electrode being electrically coupled to said input terminal,
(0) a second transistor having base, emitter, and collector electrodes, the base of said second transistor being electrically coupled to the emitter of said first transistor, said output terminal being electrically coupled to the emitter of said second transistor,
(d) a first circuit including a resistance of a predetermined value, said first circuit defining a feedback path between the collector electrode of said second 3 transistor and said common terminal for conducting current through said resistance and for producing a voltage drop across said resistance, and
(e) a second circuit defining a source of substantially constant current connected directly between the base and collector electrodes of said second transistor, and coupled to said resistance for increasing the voltage drop across said resistance.
2. A complementary emitter follower as in claim 1 wherein:
(a) said second circuit comprises a third transistor having base, collector, and emitter electrodes, the emitter-collector path of said third transistor being electrically coupled across the base-collector path of said second transistor, and further comprising:
(b) a fourth transistor having base, emitter, and collector electrodes, said base and collector electrodes being electrically coupled together and to the base of said third transistor.
3. A complementary emitter follower as in claim 2 wherein:
References Cited 10 UNITED STATES PATENTS 3,125,693 3/1964 De Clue 307-313 X 3,290,520 12/1966 Wennik 33069 X 3,310,688 3/1967 Ditkofsky 330-69 X 15 ROY LAKE, Primary Examiner L. J. DAHL, Assistant Examiner US. Cl. X.R. 20 30--19
US699437A 1968-01-22 1968-01-22 Complementary emitter follower Expired - Lifetime US3517324A (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3825850A (en) * 1972-11-28 1974-07-23 Electrospace Corp Direct-coupled audio amplifier having unbypassed emitter resistor stages
DE2636156A1 (en) * 1975-08-12 1977-02-17 Tokyo Shibaura Electric Co VOLTAGE FOLLOW-UP
JPS5281030U (en) * 1975-12-15 1977-06-16
US4078208A (en) * 1971-05-22 1978-03-07 U.S. Philips Corporation Linear amplifier circuit with integrated current injector
EP0115949A1 (en) * 1983-01-28 1984-08-15 Sony Corporation High impedance buffer
GB2223901A (en) * 1988-10-07 1990-04-18 Philips Electronic Associated Transistor follower circuit
EP0394807A2 (en) * 1989-04-27 1990-10-31 STMicroelectronics S.r.l. Voltage buffer stage with temperature-independent output
EP0586038A1 (en) * 1992-08-31 1994-03-09 National Semiconductor Corporation Local feedback stabilized emitter follower cascade

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2448446A1 (en) * 1974-10-10 1976-04-22 Budapesti Radiotechnikai Gyar Low-noise broadband preamplifier for AC AF devices - has complementary emitter-follower pair with third transistor raising two collector impedances

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3125693A (en) * 1964-03-17 Constant
US3290520A (en) * 1965-01-26 1966-12-06 Rca Corp Circuit for detecting amplitude threshold with means to keep threshold constant
US3310688A (en) * 1964-05-07 1967-03-21 Rca Corp Electrical circuits

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3125693A (en) * 1964-03-17 Constant
US3310688A (en) * 1964-05-07 1967-03-21 Rca Corp Electrical circuits
US3290520A (en) * 1965-01-26 1966-12-06 Rca Corp Circuit for detecting amplitude threshold with means to keep threshold constant

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4078208A (en) * 1971-05-22 1978-03-07 U.S. Philips Corporation Linear amplifier circuit with integrated current injector
US3825850A (en) * 1972-11-28 1974-07-23 Electrospace Corp Direct-coupled audio amplifier having unbypassed emitter resistor stages
DE2636156A1 (en) * 1975-08-12 1977-02-17 Tokyo Shibaura Electric Co VOLTAGE FOLLOW-UP
JPS5281030U (en) * 1975-12-15 1977-06-16
JPS5614573Y2 (en) * 1975-12-15 1981-04-06
EP0115949A1 (en) * 1983-01-28 1984-08-15 Sony Corporation High impedance buffer
GB2223901A (en) * 1988-10-07 1990-04-18 Philips Electronic Associated Transistor follower circuit
EP0394807A2 (en) * 1989-04-27 1990-10-31 STMicroelectronics S.r.l. Voltage buffer stage with temperature-independent output
EP0394807A3 (en) * 1989-04-27 1991-09-25 STMicroelectronics S.r.l. Voltage buffer stage with temperature-independent output
EP0586038A1 (en) * 1992-08-31 1994-03-09 National Semiconductor Corporation Local feedback stabilized emitter follower cascade
US5416365A (en) * 1992-08-31 1995-05-16 National Semiconductor Corporation Local feedback stabilized emitter follower cascade

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DE1902724A1 (en) 1969-09-04

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