EP0549381B1 - Stromspiegel mit niedrigem Wiedergabefehler - Google Patents

Stromspiegel mit niedrigem Wiedergabefehler Download PDF

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Publication number
EP0549381B1
EP0549381B1 EP92403026A EP92403026A EP0549381B1 EP 0549381 B1 EP0549381 B1 EP 0549381B1 EP 92403026 A EP92403026 A EP 92403026A EP 92403026 A EP92403026 A EP 92403026A EP 0549381 B1 EP0549381 B1 EP 0549381B1
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EP
European Patent Office
Prior art keywords
branch
transistors
current mirror
mirror
error
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92403026A
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English (en)
French (fr)
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EP0549381A1 (de
Inventor
Jean-Charles Grasset
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Teledyne e2v Semiconductors SAS
Original Assignee
Thomson SCF Semiconducteurs Specifiques
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
    • G05F3/02—Regulating voltage or current
    • G05F3/08—Regulating voltage or current wherein the variable is dc
    • G05F3/10—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics
    • G05F3/16—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices
    • G05F3/20—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
    • G05F3/26—Current mirrors
    • G05F3/265—Current mirrors using bipolar transistors only

Definitions

  • the present invention relates to a current mirror with bipolar transistors, operating with good precision even if the transistors are at very low gain.
  • bipolar transistors have characteristics that change with the conditions of use, or even during manufacture.
  • the gain in current decreases when the temperature decreases, or under the effect of light or particulate radiation.
  • the loss of gain leads to an intrinsic error of copying in the current mirrors.
  • a current mirror is an assembly, as shown in FIG. 1, which makes it possible to force through a second branch a current I0 which is, apart from errors, identical to the current I1 which flows through a first branch.
  • the first branch comprises a current source 1, a transistors 2, the collector of which is joined to the base, and a resistance 3 for feedback.
  • the second branch comprises a transistor 5 and a resistance 6 against feedback. The bases of the two transistors 2 and 5 are combined, so that the current I1 which flows in the first branch controls the current I0 forced through a load of use 7 in the second branch.
  • the relative recopy error is equal to -2 / ( ⁇ + 2) and, in most applications, with transistors whose gain is much greater than 1, this error is not the main cause of imprecision observed and it remains masked by the offset voltage of the pair of transistors or the mismatch of the feedback resistors 3 and 6. But as soon as the gain of the transistors decreases, for whatever reasons, the error due to the low gain ( ⁇ ⁇ 1) becomes predominant. Indeed, we see that the gain ⁇ occurs in the first degree and in the denominator of the equation, so that, when the gain tends towards zero, the error tends towards - 100%.
  • Wilson mirror represented in FIG. 2. It is the equivalent of a conventional mirror, in which an amplifier transistor 8 is counter-reacted by the mirror constituted by the transistors 2 and 5. On this figure as in the following figures the load 7 is no longer shown, since it does not intervene in the understanding of the invention.
  • a second known solution resides in the buffered mirror, shown in FIG. 3.
  • the transistors of the master and copy branches, respectively 2 and 5 have their base currents not taken directly from the source I1 as in the case of FIG. 1 but through an amplifier transistor 9 whose base is connected to the source I1 and the emitter at the two bases of the transistors 2 and 5, the collector of this transistor 9 is supplied by a return voltage V R.
  • the error is given by: I0 ⁇ I1 [1-2 / ( ⁇ 2 + ⁇ + 2)]
  • Some amplifiers may have a structure which is close to that of a current mirror, but which in fact is not.
  • patent US-A-4 237 414 relates to a current source with high output impedance, comprising a Darlington and a Wilson mirror, but the assembly is such that the Darlington, not feedbacked, does nothing but increase the impedance of the output branch of the Wilson mirror.
  • the patent US-A-3 843 933 in which an amplifier comprises two balanced Darlingtons, but in which there is no mirror.
  • the invention provides a solution to the problem of low gain by proposing an arrangement such that the equation of the feedback current I0 includes a term which is canceled out in the numerator, so that the error is canceled out for a low value of gain of transistors.
  • a current mirror with low feedback error is characterized in that its output (Ic) is constituted by the collectors joined together of two transistors mounted in current amplifier of type "Darlington", its input (I1) is constituted by the base of the same amplifier, this amplifier being polarized thanks to a feedback of current type -parallel operated between its transmitter and its base by a buffered type mirror fitted with feedback resistors.
  • the invention relates to a current mirror with low feedback error comprising an input branch and an output branch, as well as a "buffered" type current mirror itself constituted by a first branch.
  • this current mirror with low feedback error being characterized in that it comprises in its output branch a first Darlington type current amplifier whose collector constitutes the output of the mirror, and the base of which is joined to the input branch, this amplifier being counter-reacted in parallel-current mode by the buffered type current mirror whose master branch, connected in series with the output branch of the current mirror with low feedback error, is joined to the Darlington transmitter, and whose feedback branch, connected in series with the input branch of the current mirror with low feedback error, is assembled at the base Darlington.
  • the bases of the two transistors 2 and 5 are combined and a transistor 4 supplied with a return voltage V R is mounted as an amplifier between the collector and the base of 2.
  • the advantage of the current mirror structure according to the invention lies in the existence of a root of the numerator, which cancels the error, in the function of the error due to the gain, a function which is written: I0 ⁇ I1 [1 + (2 ⁇ - 2) / ( ⁇ 4 + 3 ⁇ 3 + 4 ⁇ 2 + 2 ⁇ +2)]
  • the gain ⁇ at low values (0-14) is given on the abscissa
  • curve 14 relates to a Wilson structure.
  • a typical curve is represented at 15 in FIG. 6, which makes it possible to compare it with the curve 14 of a Wilson mirror.
  • the positive error bump observed for gains slightly greater than 1 is only worth + 2 to + 3% and it remains negligible in this zone for which a conventional mirror is affected by an error of the order of - 40%.
  • FIG. 6 has been drawn a dotted line at the level of a gain error of the mirror equal to -10%, which is an example of a practically acceptable error.
  • This line shows that the mirror according to the invention tolerates transistors whose gain is approximately 0.75, ie 5 times lower than the gain 3.5 of the transistors necessary for a Wilson mirror, with the same loss of -10%. .
  • the interest of the transfer function which comprises an area in which ⁇ ⁇ 1, is affected neither by problems of gain matching of the transistors used nor by problems of matching the counter resistances reaction 3 and 6.
  • the curves 15, 16, 17 illustrate the influence (minimum, typical, maximum) of a mismatch of the feedback resistances of ⁇ 2% when the degeneracy voltage is set to a value approximately 250 mV.
  • the current mirror according to the invention has the advantage of having a very high output impedance at low frequency. Compared to the Wilson mirror, known to have a high output impedance, the improvement typically involves a factor of 100.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Amplifiers (AREA)

Claims (5)

  1. Stromspiegel mit niedrigem Wiedergabefehler mit einem Eingangszweig (I₁) und einem Ausgangszweig (I₀) sowie einem "gepufferten" Stromspiegel, der seinerseits von einem ersten Hauptzweig (2, 3, 4) und einem zweiten Widergabezweig (5, 6) gebildet ist, wobei dieser Stromspiegel mit niedrigem Wiedergabefehler dadurch gekennzeichnet ist, daß er in seinem Ausgangszweig (I₀) einen ersten Darlington-Stromverstärker (10 + 11) enthält, dessen Kollektor den Ausgang des Spiegels bildet und dessen Basis mit dem Eingangszweig (I₁) verbunden ist, wobei dieser Darlington-Stromverstärker (10+11) im Parallelstrombetrieb durch den gepufferten Stromspiegel gegengekoppelt ist, dessen Hauptzweig (2, 3), der in Serie mit dem Ausgangszweig (I₀) des Stromspiegels mit niedrigem Wiedergabefehler geschaltet ist, mit dem Emitter des Darlingtons (10) verbunden ist, und dessen Wiedergabezweig (5, 6), der mit dem Eingangszweig (I₁) des Stromspiegels mit niedrigem Wiedergabefehler geschaltet ist, mit der Basis des Darlingtons (11) verbunden ist.
  2. Stromspiegel nach Anspruch 1, dadurch gekennzeichnet, daß ein zweiter Darlington-Stromverstärker (12+13), dessen Basis und Kollektor kurzgeschlossen sind, symmetrisch zum ersten Darlington (10 + 11) in den Eingangszweig eingeschaltet ist, um die Kollektor-/Emitter-Spannungen Vce der Transistoren (2, 5) des gepufferten Spiegels auszugleichen.
  3. Stromspiegel nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß er aus bipolaren Transistoren mit niedriger Verstärkung (β) aufgebaut ist.
  4. Stromspiegel nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß der Wiedergabefehler des Eingangszweigs (I₁) durch den Ausgangszweig für kleine Verstärkungen (β <2) wenig von der Verstärkung (β) der Transistoren abhängt und für eine Verstärkung der Transistoren von β = 1 den Wert Null hat.
  5. Stromspiegel nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, daß der Wiedergabefehler des Eingangszweigs (I₁) durch den Ausgangszweig (I₀) wenig von der Anpassung der Gegenkopplungswiderstände (3, 6) und der Anpassung der Verstärkung (β) der Transistoren (2,4,5,10,11) abhängt.
EP92403026A 1991-11-22 1992-11-10 Stromspiegel mit niedrigem Wiedergabefehler Expired - Lifetime EP0549381B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9114405A FR2684205A1 (fr) 1991-11-22 1991-11-22 Miroir de courant a faible erreur de recopie.
FR9114405 1991-11-22

Publications (2)

Publication Number Publication Date
EP0549381A1 EP0549381A1 (de) 1993-06-30
EP0549381B1 true EP0549381B1 (de) 1995-07-12

Family

ID=9419212

Family Applications (1)

Application Number Title Priority Date Filing Date
EP92403026A Expired - Lifetime EP0549381B1 (de) 1991-11-22 1992-11-10 Stromspiegel mit niedrigem Wiedergabefehler

Country Status (4)

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US (1) US5307027A (de)
EP (1) EP0549381B1 (de)
DE (1) DE69203436T2 (de)
FR (1) FR2684205A1 (de)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE513677C2 (sv) * 1996-11-08 2000-10-23 Ericsson Telefon Ab L M Anordning för att stabilisera slutsteg jämte slutsteg
US5859568A (en) * 1997-04-11 1999-01-12 Raytheon Company Temperature compensated amplifier
US5969574A (en) * 1998-06-04 1999-10-19 Analog Devices, Inc. Low voltage current sense amplifier
US6930300B1 (en) * 2002-07-30 2005-08-16 Finisar Corporation Method and apparatus for monitoring a photo-detector in an optical transceiver

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3843933A (en) * 1973-04-06 1974-10-22 Rca Corp Current amplifier
JPS5326554A (en) * 1976-08-24 1978-03-11 Sony Corp Tr ansistor circuit
US4237414A (en) * 1978-12-08 1980-12-02 Motorola, Inc. High impedance output current source
GB2236444A (en) * 1989-09-27 1991-04-03 Motorola Inc Current mirror

Also Published As

Publication number Publication date
DE69203436T2 (de) 1995-12-14
FR2684205A1 (fr) 1993-05-28
DE69203436D1 (de) 1995-08-17
FR2684205B1 (de) 1995-02-24
EP0549381A1 (de) 1993-06-30
US5307027A (en) 1994-04-26

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