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WO2001063747A1 - Circuit de polarisation de photodiode - Google Patents

Circuit de polarisation de photodiode Download PDF

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Publication number
WO2001063747A1
WO2001063747A1 PCT/SE2001/000348 SE0100348W WO0163747A1 WO 2001063747 A1 WO2001063747 A1 WO 2001063747A1 SE 0100348 W SE0100348 W SE 0100348W WO 0163747 A1 WO0163747 A1 WO 0163747A1
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WO
WIPO (PCT)
Prior art keywords
voltage
photodiode
circuit according
amplifier
photocurrent
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.)
Ceased
Application number
PCT/SE2001/000348
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English (en)
Inventor
Gunnar Forsberg
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.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from EP00850034A external-priority patent/EP1128313A1/fr
Priority claimed from EP00850035A external-priority patent/EP1128170A1/fr
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Priority to AU2001232600A priority Critical patent/AU2001232600A1/en
Publication of WO2001063747A1 publication Critical patent/WO2001063747A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06G—ANALOGUE COMPUTERS
    • G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
    • G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
    • G06G7/24—Arrangements for performing computing operations, e.g. operational amplifiers for evaluating logarithmic or exponential functions, e.g. hyperbolic functions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits

Definitions

  • the present invention relates to a method for biasing a photodiode with a bias voltage and to a photodiode bias circuit performing said method.
  • a photodiode e.g. of PN-type with the two layers positive and negative, or of PIN-type with the three layers positive, intrinsic and negative.
  • the positive end of the diode is called an anode and the negative end is called a cathode.
  • a phototransistor may be used in a way equivalent to the photodiode and when photodiodes are discussed below, phototransistors are considered to be included in the discussion.
  • said photodiode is to measure a high optical power, such as >0,5 mW, the photodiode needs to be biased with e.g. 5 V or else the photodiode will become saturated and the photo current will thus become too small.
  • a disadvantage with known circuits for photodiodes is thus that the range of the optical power cannot be too wide.
  • An example of an application where the optical power range is wide is in systems using wavelength division multiplexing
  • WDM Wave Division Multiple Access
  • the advantage with this invention is that a photodiode bias circuit is achieved, wherein the generated photocurrent is linear in a wide range of optical power. Further, this is achieved with a simple circuit that also may be used for other purposes, which saves money, space and time.
  • Figure 1 discloses a schematic overview of a photodiode bias circuit according to the present invention.
  • Figure 2 discloses an embodiment of the first differential amplifier shown in Fig. 1.
  • Figure 3 discloses an embodiment of the comparator shown in Fig. 1.
  • Figure 4 discloses another embodiment of the comparator shown in Fig. 1.
  • Figure 6 discloses an embodiment of Fig. 5.
  • Figure 7 discloses a photo amplifier in which the photodiode bias circuit according to the present invention may be used.
  • Figure 8 discloses a schematic view of an embodiment of Fig. 7.
  • Figure 9 discloses a schematic view of another embodiment of Fig. 7.
  • Figure 10 discloses an embodiment of a practical implementation of Fig. 9.
  • Fig 1 a photodiode bias circuit according to the invention.
  • a photodiode 1 gives out a photocurrent I P .
  • the main idea is that said photocurrent I P is to be measured and compared to a threshold and that the photodiode 1 is given a bias voltage U B depending on if the photocurrent I P is above or below said threshold. It is possible to measure the photocurrent I P directly and to compare it to a threshold current. However, voltages are easier to measure and compare, so in the example in Fig. 1 the photocurrent I P is transformed to a voltage. This is done by connecting the photodiode 1 in series with a first resistor Rl .
  • the first resistor Rl may be connected either to the cathode or to the anode of the photodiode 1. However, since the anode is more sensitive it is preferred to connect the first resistor Rl to the cathode, as is shown in the figures.
  • a first differential amplifier 2 or similar is connected with its negative input to one end of the first resistor Rl and with its positive input connected to the other end of the first resistor Rl .
  • the differential amplifier 2 reads a voltage I P -R1 over the first resistor Rl .
  • the first differential amplifier 2 gives out a first voltage
  • the anode of the photodiode 1 is in this example connected to a voltage at ground level, so called virtual ground.
  • the first voltage Ul is connected to the positive input of the comparator 3 and the threshold voltage U th is connected to the negative input of the comparator 3.
  • the bias voltage U B in this case becomes a little less than 5 V.
  • the first voltage Ui is smaller than the threshold voltage U th f then the second voltage U2 from the comparator 3 becomes 0 V.
  • the bias voltage U B in this case becomes extremely close to 0 V.
  • the magnitude of the high bias voltage is chosen to suit the particular photodiode 1 that is used, depending on its inner serial resistance. However, to simplify the description, the example 5 V will be used in the following.
  • the values of the second voltage U2 given above should be changed accordingly to give the desired bias voltage U B .
  • An advantage with the invention in Fig. 1 is that it is a photodiode bias circuit that works well when the photodiode is to measure low optical powers. This is because the bias voltage U B in this case is 0 V, which minimises both dark current and the effects of the shunt resistance and thus improves linearity. Further, the invention in Fig. 1 is also a photodiode bias circuit that works well when the photodiode is to measure high optical powers. This is because the photodiode in this case gets a bias voltage U B of e.g. 5 V, which prevents the photodiode from becoming saturated too quickly and thus improves linearity. Thus, a photodiode bias circuit is achieved that works linearly in a wide optical power range.
  • the photodiode current may then be amplified in a photo amplifier 4 to for example an output voltage U ou t for whatever uses it is further intended.
  • a photo amplifier 4 may then be amplified in a photo amplifier 4 to for example an output voltage U ou t for whatever uses it is further intended.
  • U ou t an output voltage
  • a logarithmic amplifier is used as an example.
  • this photodiode circuit could also be used with linear or other amplifiers.
  • Fig. 2 is shown an example on how the first differential amplifier 2 may look.
  • the main part includes a first operational amplifier 11 with a positive input, a negative input and an output, which gives out the first voltage Ul .
  • a second resistor R2 is connected between the negative input of the first differential amplifier 2 and the negative input of the first operational amplifier 11.
  • a third resistor R3 is connected between the negative input of the first operational amplifier 11 and the output of the first operational amplifier 11.
  • a fourth resistor R4 is connected between the positive input of the first differential amplifier 2 and the positive input of the first operational amplifier 11.
  • a fifth resistor R5 is connected between the positive input of the first operational amplifier 11 and a level adjust voltage U0.
  • the level adjust voltage U0 may be ground, but it may also be used to displace the whole voltage interval used. This applies to all places where the level adjust voltage U0 is used. It is normal to choose the resistances so that the second resistor R2 and the fourth resistor R4 are equal, and so that the third resistor R3 and the fifth resistor R5 are equal. If the resistance of the first resistance Rl is much smaller than the other resistances, then the first voltage Ul may be written as:
  • the fourth resistor R4 may be complemented with some other resistors to compensate for the resistive influence from the first resistor Rl .
  • Fig. 3 is shown an embodiment of the comparator 3. It is difficult to find a commercial comparator that has a swing between 0 V and 5 V. When low optical powers are to be measured, the closer the bias voltage U B , i.e. in this case also the second voltage U2, is to 0 V, the better, i.e. the more linear, this photodiode circuit will work.
  • the second voltage U2 should in that case preferably not be higher than a few mV.
  • Commercial comparators often have difficulties in getting that close to 0 V.
  • the comparator 3 includes an inverter 13 and an inner comparator 12 with a positive and a negative input and an output.
  • the positive input of the inner comparator 12 is used as the negative input of the comparator 3 and vice versa, due to the following inverter 13.
  • the inverter 13 is e.g. of CMOS-type it will have the same logical output as its supply voltage.
  • the inverter 13 is supplied with 0 V and 5 V, its output will change between 0 V and 5 V, which is exactly what is wanted.
  • the main issue is not that it is an inverter, but that it has the output that is wanted.
  • the same result could be achieved with e.g. another CMOS-circuit or with a comparator with CMOS-type output.
  • a sixth resistor R6 is connected between the power supply voltage V cc and the positive input of the inner comparator 12.
  • a seventh resistor R7 is connected between the level adjust voltage UO and the positive input of the inner comparator 12.
  • a eighth resistor R8 is connected between the positive input and the output of the inner comparator 12.
  • the threshold voltage U t h is created on the positive input of the inner comparator 12 with a level adjustment from the level adjust voltage UO . If the circuit should be arranged so that the threshold voltage U th feeds the negative input of the inner comparator 12, then the positive input of the inner comparator 12 should be fed from a low-resistance source in order that the positive feedback is precisely determined, i.e. the resistances should be selected so that R7 «R8.
  • the bias voltage it is possible to change the bias voltage both fast and slow.
  • a photodiode have a certain capacitance between its anode and cathode. This leads to that when the voltage is changed over the photodiode, then a transient current is generated proportionally to the derivative of the voltage change. Thus, one would believe that it would be better to change the bias voltage slowly. However, if the bias voltage is changed slowly, then the total circuit will become slow and rapid changes in optical power will not be measured. Thus, the preferred embodiment is to change the bias voltage fast. When the bias voltage is raised, then said transient current will have a rather small influence compared to the large photo current. Instead there will be a problem when the optical power and thus the bias voltage is lowered. That is because the charge between the cathode and the anode of the photodiode will totally cut-off the photo amplifier. Thus, the photo amplifier will consider that it is measuring total darkness and will do that until the photocurrent has restored the real charge.
  • a solution to this problem is shown in Fig. 5.
  • a charge compensation capacitor Cl is introduced between the anode of the photodiode 1 and the output of the comparator 3 over a second inverter 15. The purpose is to generate a second transient current with the opposite sign as the first transient current produced by the photodiode 1 when the bias voltage is changed.
  • the capacitance of the charge compensation capacitor Cl is somewhat larger than the capacitance of the photodiode 1. What will happen is then this: When the bias voltage U B suddenly goes down to 0 V, then a first transient current will come out from the input of the photo amplifier 4 through the photodiode. A few ns later a somewhat larger second transient current will be produced by the charge compensation capacitor Cl in the opposite direction. If the photo amplifier 4 is normally slow it will only feel a small fast sum transient current in the right direction, i.e. into its input. This means that the output voltage U out will experience a fast positive transient and then regain its correct value without ever going below said correct value. Thus, the photo amplifier 4 and subsequent circuits will never believe that it is dark simply because the bias voltage U B suddenly is lowered.
  • the isolator 16 may be implemented in numerous ways and one alternative is shown in Fig. 6. The man skilled in the art can easily adopt other versions with equivalent function.
  • a second capacitor C2 is on one end connected to the output of the second inverter 15 and on its other end, at the first potential VI, to the anode of a first diode, to a ninth resistor R9 and to a tenth resistor RIO.
  • the tenth resistor RIO is further connected to ground.
  • the cathode of the first diode Dl is connected, at the second potential V2, to the charge compensation capacitor Cl and to the anode of a second diode D2.
  • the cathode of the second diode D2 is further connected, at the third potential V3, to the ninth resistor R9.
  • the second capacitor C2 should be chosen with a higher capacitance than the charge compensation capacitor Cl, because in that case the second capacitor C2 will discharge slower than the charge compensation capacitor Cl.
  • the second capacitor C2 discharges over the tenth resistor RIO to ground. When it is completely discharged, the first potential VI will once again become 0 V and the first diode Dl will stop conducting. The second potential V2 will discharge again over the second diode D2 and the ninth resistor R9. Thus, the status quo is once again reached.
  • the second capacitor C2 will be charged and the first potential VI will decrease to -5 V.
  • the second capacitor C2 will then charge and discharge much like in the previous example, but with the current in the opposite direction, and the first potential VI will return to 0 V.
  • a preferred embodiment is that the transient current from the charge compensation capacitor Cl should not be very high when the photo current I P is high, as explained above. In that case the resistances of the ninth resistor R9 and the tenth resistor RIO should be rather high. That is because that leads to that only a small current flows from the second potential V2 to the first potential VI over the second diode D2 and the ninth resistor R9. Thus, the charge compensation capacitor Cl is charged slower and a smaller transient current will occur.
  • An advantage with the last embodiments of the present invention is that the automatic change of the bias voltage is so smooth that it is possible to have a high bandwidth without getting problems with disturbances.
  • the photo amplifier 4 used to amplify the photocurrent may look in different ways.
  • One logarithmic version is shown in Fig. 7.
  • the photo current I P is fed into the negative input of a second operational amplifier 21.
  • the positive input of the second operational amplifier 21 is connected to ground and there is a first transistor TI connected between the negative input and the output of the second operational amplifier 21.
  • the first transistor Tl is connected with its collector and base to the negative input of the second operational amplifier 21 and with its emitter to the output of the second operational amplifier 21, but other connections are possible. Especially it is possible to instead connect the base to ground. It is also possible to use a diode instead of the first transistor Tl. This connection of a transistor or a diode makes the output voltage of the second operational amplifier 21 a logarithmic function of any current, such as the photocurrent I P . It is of course possible to use an input voltage instead, together with an input resistor. Said output voltage will from now on be called the third voltage U3 for short.
  • the current flowing through the first transistor Tl is approximately equal to the photo current I P . If the first transistor Tl has a first inherent temperature dependent constant kl, then the third voltage U3 will become :
  • I 0 ⁇ is the reverse leakage current for the first transistor Tl.
  • the formula applies only approximately and only for currents that are not very small or large.
  • a behaviour in an ordinary transistor with a first constant kl of 0.06 V and a reverse leakage current I 0 ⁇ of 10 ⁇ 13 A could be that if the temperature is stable, then the voltage over the first transistor Tl increases about 60 mV when the current flowing through it increases 10 times, which in this case corresponds to an increase in optical power of 10 dB.
  • the difference is taken between the third voltage U3 and a fourth voltage U4 that is used as a reference. If the fourth voltage U4 have approximately the same temperature dependency as the third voltage U3, then they will be affected approximately equal from temperature changes and the difference between them will thus take away most of said temperature " dependency.
  • the fourth voltage U4 may be accomplished by using a reference current I refc which enters the negative input of a third operational amplifier 22 that has a second transistor or diode T2 connected in the same way as the second operational amplifier 21 has.
  • the fourth voltage U4 is taken from the output of the third operational amplifier 22 and is thus a logarithmic function of the reference current I rer If the second transistor T2 has a second inherent temperature dependent constant k2, then the fourth voltage U4 becomes:
  • the reference current I ref in the middle of the interval where measuring is intended. This is because the measuring error due to temperature dependence will be smaller the closer the photocurrent I P is to the reference current I re f- Thus, if it is a wish to measure photocurrents from 0,1 ⁇ A to 1 mA it is appropriate that the reference current I re f is approximately 10 ⁇ A.
  • the easiest way of implementing this circuit is to chose transistors Tl and T2 that have similar temperature characteristics and place them close together, so as to keep them in the same temperature. It is preferable to place them in the same integrated circuit.
  • the third voltage U3 and the fourth voltage U4 enters a second differential amplifier 23, which gives out a fifth voltage U5.
  • a sixth voltage U6 may be entered into the differential amplifier if there is a wish to level adjust the interval within which the fifth voltage U5 may be.
  • the sixth voltage U6 may be the same as the level adjust voltage U0 or something else.
  • Fig. 7 is also shown an example on how the second differential amplifier 23 may look.
  • the main part includes a fourth operational amplifier 24 with a positive input, a negative input and an output, which gives out the fifth voltage U5.
  • An eleventh resistor Rll is connected between the negative input of the second differential amplifier 23 and the negative input of the fourth operational amplifier 24.
  • a twelfth resistor R12 is connected between the negative input of the fourth operational amplifier 24 and the output of the fourth operational amplifier 24.
  • a thirteenth resistor R13 is connected between the positive input of the second differential amplifier 23 and the positive input of the fourth operational amplifier 24.
  • a fourteenth resistor R14 is connected between the positive input of the fourth operational amplifier 24 and the sixth voltage U6.
  • the fifth voltage U5 may be written as:
  • transistors and diodes normally have an inner serial resistance, e.g. 0,5 ⁇ , between collector and emitter or between anode and cathode, respectively. This may cause a notable error for currents larger than approximately 0,1 mA due to unwanted voltage- drop over the inner resistance. This may be compensated by subtracting a compensation voltage U c from the output voltage
  • Said compensation voltage U c should be proportional to the photocurrent I P and when there is no photocurrent I P , then the compensation voltage U c should be equal to zero. This can be accomplished in practise in many ways. An example is shown schematically in Fig. 8. Since the fifth voltage U5 is level adjusted by the sixth voltage U6, see (4), said sixth voltage U6 may be used to correct the fifth voltage U5 and thus the output voltage U out by taking:
  • the first voltage Ul is proportional to the photocurrent I P , however with a level adjustment UO, see (1), and the compensation voltage can thus be accomplished by:
  • An advantage with this embodiment is that the same circuit - the first differential amplifier 2 - may be used for two purposes, i.e. to create the bias voltage U B for the photodiode and to create the compensation voltage U c . This saves components and space and further reduces the time for manufacturing. However, it would be equally possible to have separate circuits for the two purposes.
  • a further alternative solution is to put an inverting amplifier 31 on the output of the second differential amplifier 23, see Fig. 9, thus making the output voltage U out the inverse of the fifth voltage U5 according to:
  • Fig. 10 is shown a practical implementation of Fig. 9.
  • a trimming potentiometer R tp is connected with its ends between the first voltage Ul and the level adjust voltage UO.
  • a fifteenth resistor R15 is connected between the sixth voltage U6 and the middle connection of the trimming potentiometer R tp .
  • a sixteenth resistor R16 is connected between the sixth voltage U6 and the level adjust voltage UO.
  • the twelfth resistor R12 in the second differential amplifier 23 may then be complemented by a seventeenth resistor R17 and a eighteenth resistor R18 in order to compensate for resistive influence of the fifteenth resistor R15 and the sixteenth resistor R16.
  • the inverting amplifier 31 may be any inverting amplifier. However, even though the temperature dependence in the photo amplifier 4 partly is reduced by taking the difference between what is measured and a reference, there is still the second temperature dependency in the fifth voltage U5 that is proportional to the absolute temperature T in Kelvin. Thus, it would be good to include a circuit with a temperature dependency that is proportional to the inverse of the absolute temperature and the inverting amplifier 31 may be used for that purpose.
  • Fig. 11 is shown an example of such an inverting amplifier. It includes a fifth operational amplifier 32 with a nineteenth resistor R19 on its negative input, with the level adjust voltage UO on its positive input and a twentieth resistor R20 between its negative input and its output. The use of only those resistors and with the fifth voltage U5 connected to the nineteenth resistor R19 would give an output voltage U ou t of:
  • the temperature dependent resistor R ⁇ should have a temperature close to that of the transistors Tl, T2. This is easiest implemented in practise if the temperature dependent resistor R ⁇ and the transistors Tl, T2 are placed close to each other and if the circuit is so dimensioned that the power in the temperature dependent resistor R ⁇ is not so high that self-heating occurs.

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  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
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Abstract

La présente invention concerne un procédé de polarisation d'une photodiode (1) au moyen d'une tension de polarisation (UB), ainsi qu'un circuit de polarisation de photodiode permettant la mise en oeuvre de ce procédé. Ladite photodiode (1) produit un courant photoélectrique (IP). Selon l'invention, le procédé en question consiste à lire une mesurande (U1) associée à ce courant photoélectrique (IP), à comparer cette mesurande (U1) avec un seuil (Uth), et à conférer à la tension de polarisation (UB) une amplitude variant selon que la mesurande (U1) est supérieure ou inférieure au seuil (Uth).
PCT/SE2001/000348 2000-02-25 2001-02-14 Circuit de polarisation de photodiode Ceased WO2001063747A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001232600A AU2001232600A1 (en) 2000-02-25 2001-02-14 Photodiode bias circuit

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP00850034A EP1128313A1 (fr) 2000-02-25 2000-02-25 Amplificateur logarithmique
EP00850035A EP1128170A1 (fr) 2000-02-25 2000-02-25 Circuit de polarisation pour photodiode
EP00850034.0 2000-02-25
EP00850035.7 2000-02-25

Publications (1)

Publication Number Publication Date
WO2001063747A1 true WO2001063747A1 (fr) 2001-08-30

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PCT/SE2001/000348 Ceased WO2001063747A1 (fr) 2000-02-25 2001-02-14 Circuit de polarisation de photodiode
PCT/SE2001/000347 Ceased WO2001063746A1 (fr) 2000-02-25 2001-02-16 Amplificateur logarithmique

Family Applications After (1)

Application Number Title Priority Date Filing Date
PCT/SE2001/000347 Ceased WO2001063746A1 (fr) 2000-02-25 2001-02-16 Amplificateur logarithmique

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WO (2) WO2001063747A1 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992622A (en) * 1974-11-25 1976-11-16 Fuji Photo Optical Co., Ltd. Logarithmic amplifier with temperature compensation means
US4216379A (en) * 1978-10-26 1980-08-05 Sprague Electric Company Low voltage bias circuit for a photo-diode

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2220925B1 (fr) * 1973-02-27 1976-04-30 Thomson Csf
JPH0748624B2 (ja) * 1988-06-20 1995-05-24 三菱電機株式会社 対数増幅器

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3992622A (en) * 1974-11-25 1976-11-16 Fuji Photo Optical Co., Ltd. Logarithmic amplifier with temperature compensation means
US4216379A (en) * 1978-10-26 1980-08-05 Sprague Electric Company Low voltage bias circuit for a photo-diode

Also Published As

Publication number Publication date
AU2001232600A1 (en) 2001-09-03
WO2001063746A1 (fr) 2001-08-30
AU2001234302A1 (en) 2001-09-03

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