CA1223300A - Circuit arrangement for driving a current-controlled component - Google Patents
Circuit arrangement for driving a current-controlled componentInfo
- Publication number
- CA1223300A CA1223300A CA000444754A CA444754A CA1223300A CA 1223300 A CA1223300 A CA 1223300A CA 000444754 A CA000444754 A CA 000444754A CA 444754 A CA444754 A CA 444754A CA 1223300 A CA1223300 A CA 1223300A
- Authority
- CA
- Canada
- Prior art keywords
- current
- light
- transistor
- circuit arrangement
- emitting element
- 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
Links
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- Semiconductor Lasers (AREA)
Abstract
ABSTRACT:
"Circuit arrangement for driving a current-controlled component."
In a circuit arrangement for driving a current-controlled component, the current-controlled component, a controllable resistance and a current source are arranged in series. A current branch including a capacitor is arranged in parallel with the series arrangement formed by the controllable resistance and the current-controlled component.
"Circuit arrangement for driving a current-controlled component."
In a circuit arrangement for driving a current-controlled component, the current-controlled component, a controllable resistance and a current source are arranged in series. A current branch including a capacitor is arranged in parallel with the series arrangement formed by the controllable resistance and the current-controlled component.
Description
33~
PHT. 82.344 The invention relates to a circuit arrangement Eor driving a current-controlled ccmponent in which the current-controlled component, a controllable resistance and a current source are arranged in series.
Current-controlled components are, for example, lasers and light-emitting diodes used as transmitting elements in the optical message transmission comprising optical fibres and a transmission medium. Therein, the light intensity of the laser or of the light-emitting diode is m~dulated by the input signal. In the digital optical message transmission the transmission of light correspon~s to, for example, a logic 1, whereas a logic 0 is present when no light is transmittedO
In The Bell System, Technical Journal, Vol. 57, No. 6, July-August 1978 a la æ r transmitter for optical transmission systems is disclosed on pages 1823 to 1833 in the article "Ga~lAs Laser Trans-mitter for Lightwave Transmission Systems" by Shumate, Chen and Dorman.
Figure 2 on page 1826 shows a circuit arrangement for dri~ing a laser, which is here shown in Figure 1. Figure 2 shows a first embodiment of the invention and Figure 3 a second embodiment, while the characteris-tic curve of a laser is shown in Figure 4.
In Figure 1, the input signal is applied via a transfer stage comprising a transistor Q3 to one input of a differential amplifier which comprises two transistors Ql and Q2. The other input of the differential amplifier is connected to a reference voltage. A resis-tor having a value of 10 ~ is included in the collector lead of the transistor Ql' while the laser is arranged in the collector-lead of the transistor Q2. m e emitters of -the two transistors Ql and Q2 are connected to one output of a current source. When the laser is to transmit light, the transistor Q2 is rendered conductive, whereas the transistor Ql is cut off, so that the current source is connected to the laser via the emitter-collector path of the transistor Q2. If no light is to be transmitted, that is to say there is a pulse pause, the transistor Q2 is cut-off, whereas transistor Ql is rendered con-ductive, so that the c~ ent source is not operated in the no-load m~de, but the current circui-t is closed vla the emitter-collector path 3~iD
PHT. 82.344 2 of the transistor Ql and the 10 ~ -resistor.
This prior art circuit arrangement has the disadvantage that it has a comparati~rely high power dissipation, as during the pulse pauses the current produced by the current source does not 1aw through the laser, but through the 10 J~ - resistor, in which now ohmic losses occur.
The invention has for its object to provide a circuit arrangement with reduced power loss for driving a current-controlled component.
According to the invention, this object is accomplished in that a current branch comprising a first capacitor is provided in parallel with the series arrangement formed by the controllable resis-tan~e and the current-controlled component.
The sub-claims describe advantageous embodiments of the invention.
In Figure 2, an input signal UE is applied vla a capacitor Cl to the base of a transistor T, which is connected to ground via a resistor Rl and to the supply voltage -Us via a resistor R2. The emitter of the transistor T is connected to the supply voltage -UB
via a current source Q, whereas its collector is connected to ground via a laser or a light-emitting diode L, denoted by IED in the .
further course of the description. ~ capacitor C2 connects the emitter of the transistor T to ground.
The resistors Rl and R2 are used to adjust the operating point of the transistor T~ The digital input signal UE which is applied to the base of the transistor T via the capacitor Cl, (a.c.
coupling) modulates the light intensity of the laser or the LED.
During the transmission ~f a light pulse by the laser or the LED the transistor is ren~ered cond~ctive, whereas it is cut-off 3Q during a pulse pause, so that the current from the current source Q
flGws as a charging current into the capacitor C2. For a subsequent tra~smission of a light pulse the transistor beccmes conductive again.
m e current for the laser or the LED are now produced jointly by the current source Q and the char~ed capacitor C2. In the then subse-quent pulse pause the capacitor C2 is again charged by the currentsource Q.
Whilst during the pulse pauses the current from the current source does not pxoduce ohmic losses in a resistor, but only provides ~2Z33()~
PHT ~2.344 -3_ 25.11.1983 chargin~ of a capacitor and at each pulse subsequent to a pulse pause is again appl-ed to t.he laser or to the LED, the current source needs only t.o produce half of the current it must produce in the pr~or art circuit.
arrangement.. In other words, when the transistor ls operated as a switch only half the power is consumed.
For a current.-controlled component. havtn~ a threshold value, as, for example, in the case of a laser, it: may be wise not to cut-off t.he transistor completely, but. to send a bias current t.hrou~h the current-controlled component., as will be further described hereafter wlth referencr? t.o t.he character sti.c curve of a laser which is shown ln Flgure 4.
In order t.o oht.ain an adequatel~ hl~h li~ht int.ens~ty, it. is necessary t.o operate t.he laser in t.he st.eep port.ion of the curve after t.he hend. To that end An avera~e power PM is establ;shed as an operat.ing point. around which t.he supplied li~ht power fluctuates. The point PM is est.abl-shed by t.he quiescent current..IC. Half the pulse current 1/2 A IC
which s proportional to the fluct.uations ~ UE of the input. volta~e UF.
is now only superirnposed on the quiescent. current IC. During a pulse pause in t.he lnput slgnal the capacitor C2 takes up half the pulse current. 1/2 ~ IC, which it applles again t.o the laser during the subsequent. pulse. At t.he moment. at. which the collector current. t.hrou~h t.he trans-stor and also through the laser consequently assurnes the values IC + 1/2 4 IC and IC - 1/2 ~IC, t.hen the laser transmits light having t.he lntensities PM ~ 1/2 ~ PM and PM - 1/2 apM. Then t.he current IC~ 1/2 ~ IC and the ll~ht. int.en~sit.y PM + 1/2 ~ PM corresponrl to a pulse, whereas t.he current IC - 1/2 4IC and the light intensity PM - 1/2 ~ PM represent. a pulse pause. The pulse current ~ IC depends on t.he quiescent. current IC in accordance wit.h t.he followin~ formula:
IC
~ IC ~ UT .~UE
where UT i.s t.he ther~ovolta~e of t.he t.ransist.or.
The dependence of t.he pulsr? current. ~ IC on the quiescent current IC can br.? reriuced by means of nr-?~ative feedback.
~ 11e embod~ment shown in Figure 3 differs t.opologically from t.he embodiment. shown in Fl~ure 2 only hy a neFatlve feedback resistor R3 arran~ed brtween the current source Q and the emitt.er of t.he ~ ~ ~ 3 3 ~ ~
RHT (~2. 3lJ4 _4_ 25.11.1983 transistor T. The capacltor C2 is arran~ed in parallel with t,he ser~'es arrangement formed by the laser L, the collect,or-em.itter path of t,ranslst.or T and the ne~ative feedback resist,or R3. In thls case, t.he pulse current ~ IC depends on t,he qu.~escent current IC in accordance w~t,h the rollowi~ng formula:
4 IC = [~I ~ R3 4 UE
IC
The dependence of t.he pulse current. ~ IC on the quiescent. current IC ~s consequently reduced by t.he factor - -R3-~rT
O 1+ IC
PHT. 82.344 The invention relates to a circuit arrangement Eor driving a current-controlled ccmponent in which the current-controlled component, a controllable resistance and a current source are arranged in series.
Current-controlled components are, for example, lasers and light-emitting diodes used as transmitting elements in the optical message transmission comprising optical fibres and a transmission medium. Therein, the light intensity of the laser or of the light-emitting diode is m~dulated by the input signal. In the digital optical message transmission the transmission of light correspon~s to, for example, a logic 1, whereas a logic 0 is present when no light is transmittedO
In The Bell System, Technical Journal, Vol. 57, No. 6, July-August 1978 a la æ r transmitter for optical transmission systems is disclosed on pages 1823 to 1833 in the article "Ga~lAs Laser Trans-mitter for Lightwave Transmission Systems" by Shumate, Chen and Dorman.
Figure 2 on page 1826 shows a circuit arrangement for dri~ing a laser, which is here shown in Figure 1. Figure 2 shows a first embodiment of the invention and Figure 3 a second embodiment, while the characteris-tic curve of a laser is shown in Figure 4.
In Figure 1, the input signal is applied via a transfer stage comprising a transistor Q3 to one input of a differential amplifier which comprises two transistors Ql and Q2. The other input of the differential amplifier is connected to a reference voltage. A resis-tor having a value of 10 ~ is included in the collector lead of the transistor Ql' while the laser is arranged in the collector-lead of the transistor Q2. m e emitters of -the two transistors Ql and Q2 are connected to one output of a current source. When the laser is to transmit light, the transistor Q2 is rendered conductive, whereas the transistor Ql is cut off, so that the current source is connected to the laser via the emitter-collector path of the transistor Q2. If no light is to be transmitted, that is to say there is a pulse pause, the transistor Q2 is cut-off, whereas transistor Ql is rendered con-ductive, so that the c~ ent source is not operated in the no-load m~de, but the current circui-t is closed vla the emitter-collector path 3~iD
PHT. 82.344 2 of the transistor Ql and the 10 ~ -resistor.
This prior art circuit arrangement has the disadvantage that it has a comparati~rely high power dissipation, as during the pulse pauses the current produced by the current source does not 1aw through the laser, but through the 10 J~ - resistor, in which now ohmic losses occur.
The invention has for its object to provide a circuit arrangement with reduced power loss for driving a current-controlled component.
According to the invention, this object is accomplished in that a current branch comprising a first capacitor is provided in parallel with the series arrangement formed by the controllable resis-tan~e and the current-controlled component.
The sub-claims describe advantageous embodiments of the invention.
In Figure 2, an input signal UE is applied vla a capacitor Cl to the base of a transistor T, which is connected to ground via a resistor Rl and to the supply voltage -Us via a resistor R2. The emitter of the transistor T is connected to the supply voltage -UB
via a current source Q, whereas its collector is connected to ground via a laser or a light-emitting diode L, denoted by IED in the .
further course of the description. ~ capacitor C2 connects the emitter of the transistor T to ground.
The resistors Rl and R2 are used to adjust the operating point of the transistor T~ The digital input signal UE which is applied to the base of the transistor T via the capacitor Cl, (a.c.
coupling) modulates the light intensity of the laser or the LED.
During the transmission ~f a light pulse by the laser or the LED the transistor is ren~ered cond~ctive, whereas it is cut-off 3Q during a pulse pause, so that the current from the current source Q
flGws as a charging current into the capacitor C2. For a subsequent tra~smission of a light pulse the transistor beccmes conductive again.
m e current for the laser or the LED are now produced jointly by the current source Q and the char~ed capacitor C2. In the then subse-quent pulse pause the capacitor C2 is again charged by the currentsource Q.
Whilst during the pulse pauses the current from the current source does not pxoduce ohmic losses in a resistor, but only provides ~2Z33()~
PHT ~2.344 -3_ 25.11.1983 chargin~ of a capacitor and at each pulse subsequent to a pulse pause is again appl-ed to t.he laser or to the LED, the current source needs only t.o produce half of the current it must produce in the pr~or art circuit.
arrangement.. In other words, when the transistor ls operated as a switch only half the power is consumed.
For a current.-controlled component. havtn~ a threshold value, as, for example, in the case of a laser, it: may be wise not to cut-off t.he transistor completely, but. to send a bias current t.hrou~h the current-controlled component., as will be further described hereafter wlth referencr? t.o t.he character sti.c curve of a laser which is shown ln Flgure 4.
In order t.o oht.ain an adequatel~ hl~h li~ht int.ens~ty, it. is necessary t.o operate t.he laser in t.he st.eep port.ion of the curve after t.he hend. To that end An avera~e power PM is establ;shed as an operat.ing point. around which t.he supplied li~ht power fluctuates. The point PM is est.abl-shed by t.he quiescent current..IC. Half the pulse current 1/2 A IC
which s proportional to the fluct.uations ~ UE of the input. volta~e UF.
is now only superirnposed on the quiescent. current IC. During a pulse pause in t.he lnput slgnal the capacitor C2 takes up half the pulse current. 1/2 ~ IC, which it applles again t.o the laser during the subsequent. pulse. At t.he moment. at. which the collector current. t.hrou~h t.he trans-stor and also through the laser consequently assurnes the values IC + 1/2 4 IC and IC - 1/2 ~IC, t.hen the laser transmits light having t.he lntensities PM ~ 1/2 ~ PM and PM - 1/2 apM. Then t.he current IC~ 1/2 ~ IC and the ll~ht. int.en~sit.y PM + 1/2 ~ PM corresponrl to a pulse, whereas t.he current IC - 1/2 4IC and the light intensity PM - 1/2 ~ PM represent. a pulse pause. The pulse current ~ IC depends on t.he quiescent. current IC in accordance wit.h t.he followin~ formula:
IC
~ IC ~ UT .~UE
where UT i.s t.he ther~ovolta~e of t.he t.ransist.or.
The dependence of t.he pulsr? current. ~ IC on the quiescent current IC can br.? reriuced by means of nr-?~ative feedback.
~ 11e embod~ment shown in Figure 3 differs t.opologically from t.he embodiment. shown in Fl~ure 2 only hy a neFatlve feedback resistor R3 arran~ed brtween the current source Q and the emitt.er of t.he ~ ~ ~ 3 3 ~ ~
RHT (~2. 3lJ4 _4_ 25.11.1983 transistor T. The capacltor C2 is arran~ed in parallel with t,he ser~'es arrangement formed by the laser L, the collect,or-em.itter path of t,ranslst.or T and the ne~ative feedback resist,or R3. In thls case, t.he pulse current ~ IC depends on t,he qu.~escent current IC in accordance w~t,h the rollowi~ng formula:
4 IC = [~I ~ R3 4 UE
IC
The dependence of t.he pulse current. ~ IC on the quiescent. current IC ~s consequently reduced by t.he factor - -R3-~rT
O 1+ IC
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A circuit arrangement for driving a current-con-trolled light-emitting element to emit pulses of light in intervals corresponding to input signal pulses, comprising:
a direct current power source;
a transistor having an emitter, base and collec-tor and a main current path between the emitter and collec-tor, the resistance of such main current path being con-trollable from a relatively high to a relatively low value by a signal applied to the base of the transistor;
a constant current source arranged in series with said light-emitting element and the main current path of the transistor, such series arrangement being connected to said direct current power source;
a capacitor in parallel with the series combina-tion of said light-emitting element and the main current path of said transistor;
and means for coupling input signal pulses to the base of said transistor to control the resistance of the main current path thereof, such resistance decreasing from its high to its low value during each such pulse;
whereby during each input signal pulse said cur-rent source and said capacitor supply current to said light-emitting element, causing it to emit a pulse of light, and during each interval between signal pulses said current source supplies charging current to said capacitor.
a direct current power source;
a transistor having an emitter, base and collec-tor and a main current path between the emitter and collec-tor, the resistance of such main current path being con-trollable from a relatively high to a relatively low value by a signal applied to the base of the transistor;
a constant current source arranged in series with said light-emitting element and the main current path of the transistor, such series arrangement being connected to said direct current power source;
a capacitor in parallel with the series combina-tion of said light-emitting element and the main current path of said transistor;
and means for coupling input signal pulses to the base of said transistor to control the resistance of the main current path thereof, such resistance decreasing from its high to its low value during each such pulse;
whereby during each input signal pulse said cur-rent source and said capacitor supply current to said light-emitting element, causing it to emit a pulse of light, and during each interval between signal pulses said current source supplies charging current to said capacitor.
2. A circuit arrangement as claimed in Claim 1, wherein the current-controlled element is one of a laser and a light-emitting diode.
3. A circuit arrangement as claimed in Claim 1, and further comprising means for providing a DC reference bias on the base of said transistor.
4. A circuit arrangement as claimed in Claim 1, wherein the current source and the capacitor are connected to the emitter of the transistor and the light-emitting element is connected to the collector of the transistor.
5. A circuit arrangement as claimed in Claim 4, wherein said light-emitting element is one of a laser and a light-emitting diode.
6. A circuit arrangement as claimed in Claim 4, further comprising a negative feedback resistor connected between the emitter of the transistor and said current source; said capacitor being in parallel with the series combination formed by said light-emitting element, the main current path of the transistor and said negative feed-back resistor.
7. A circuit arrangement as claimed in Claim 6, wherein the current controlled element is one of a laser and a light-emitting diode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000444754A CA1223300A (en) | 1984-01-05 | 1984-01-05 | Circuit arrangement for driving a current-controlled component |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000444754A CA1223300A (en) | 1984-01-05 | 1984-01-05 | Circuit arrangement for driving a current-controlled component |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223300A true CA1223300A (en) | 1987-06-23 |
Family
ID=4126882
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000444754A Expired CA1223300A (en) | 1984-01-05 | 1984-01-05 | Circuit arrangement for driving a current-controlled component |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1223300A (en) |
-
1984
- 1984-01-05 CA CA000444754A patent/CA1223300A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |