Background technology
In optical communication system, laser driver (LDD, Laser Diode Driver) and laser are the important composition elements of transmitting terminal, and laser driver is that laser provides drive current.To laser the characteristic of threshold current is arranged, this drive current comprises ac modulated current and dc bias current, and modulated current wherein is exactly the high-speed digital signal of transmission, and bias current is mainly used in the threshold value of opening laser.
The performance parameter of laser can change along with temperature.Referring to shown in Figure 1, along with the rising of temperature, very big drift can take place in the threshold current of laser diode, and electro-optical efficiency can successively decrease thereupon simultaneously.Laser great majority require to be operated in-40 ℃~85 ℃ the temperature range, keep stablizing of average light power and extinction ratio.But when temperature changed, the threshold current of laser can change, and is constant in order to guarantee average light power, just need control the size of adjusting bias current through automated power.When the bias current of automated power control changed, if modulated current is constant, then the variation of extinction ratio can exceed normal range (NR).
In order to eliminate the influence of variations in temperature to laser characteristic, present most of lasers all are directed against modulated current and carry out temperature-compensating, and the extraneous refrigerating system of the employing that has is carried out Physical temperature-lowering, and the temperature-compensation circuit of the employing chip internal that has compensates modulation.In practical application, when the temperature characterisitic of laser not simultaneously, needed penalty coefficient is also inequality, compensating circuit also just needs to change thereupon.But the compensation method that proposes at present generally lacks flexibility, and the temperature-compensating that provides is relatively fixing, is difficult to adapt to the temperature characterisitic of different laser device.
Summary of the invention
The objective of the invention is in order to overcome the deficiency of above-mentioned background technology; A kind of optical communication laser driver modulated current proportional compensation circuit is provided; Can be in the condition and range of operate as normal; Realize that the output modulated current is the fixed proportion relation of bias current, and this proportionate relationship can be provided with through the resistance that changes peripheral resistance by the user, realize adjusting easily the needed penalty coefficient of laser; It is stable to keep the extinction ratio of laser in full temperature scope, simultaneous adaptation different laser actuator temperature characteristic.
Optical communication laser driver modulated current proportional compensation circuit provided by the invention; Comprise reference current source, first current mirror, current ratio amplifier, second current mirror, modulated current output module and bias current output module; Said reference current source is used to provide current reference; Said first current mirror links to each other with reference current source, current ratio amplifier and bias current output module respectively, is used for the reference current of reference current source output is mirrored to bias current output module and current ratio amplifier respectively; Said current ratio amplifier is connected between first current mirror and second current mirror, is used for current compensation, outputs to second current mirror after the current signal amplification with the output of first current mirror; Said second current mirror also links to each other with the modulated current output module, is used for the current controling signal after amplifying is outputed to the modulated current output module; Said modulated current output module is used for the current controling signal according to the input of second current mirror, will convert modulated current signal into by the modulation signal of signal end input, and said modulated current signal is outputed to semiconductor laser; Said bias current output module is used for generating bias current signal according to the current signal of first current mirror input, and said bias current signal is outputed to semiconductor laser.
In technique scheme; Said first current mirror is made up of the first transistor, transistor seconds and the 3rd transistor; The first transistor, transistor seconds and the 3rd transistorized grid link to each other, and the grid of the first transistor links to each other with drain electrode, also links to each other with an end of reference current source; The other end ground connection of reference current source; The drain electrode of transistor seconds links to each other with the bias current output module, and the 3rd transistor drain links to each other with the current ratio amplifier, and the first transistor, transistor seconds and the 3rd transistorized source electrode connect power supply.
In technique scheme; Said current ratio amplifier is made up of amplifier, first resistance and second resistance; Amplifier's inverting input links to each other with an end of the 3rd transistor drain and first resistance respectively; In-phase input end links to each other with an end of second current mirror and second resistance respectively, and output links to each other with second current mirror, the equal ground connection of the other end of first resistance and second resistance.
In technique scheme; Said second current mirror is made up of the 4th transistor and the 5th transistor; The 4th transistor links to each other with the output of amplifier with the 5th transistorized grid; The 4th transistor drain links to each other with the in-phase input end of amplifier, and the 5th transistor drain links to each other with the modulated current output module, and the 4th transistor and the 5th transistorized source electrode connect power supply.
In technique scheme, two modulation signal inputs of said modulated current output module connect 2 road modulating input signals respectively, Current Control termination the 5th transistor drain, the semiconductor laser negative terminal of modulated current output termination laser assembly.
In technique scheme, the drain electrode of the Current Control termination transistor seconds of said bias current output module, the semiconductor laser negative terminal of bias current output termination laser assembly.
Compared with prior art, advantage of the present invention is following:
(1) in the condition and range of operate as normal; When causing the characteristics of luminescence to change when the operation conditions change of semiconductor laser; The modulated current output of circuit provided by the present invention can keep and the fixing proportionate relationship of bias current output automatically, levels off to constant with the extinction ratio that guarantees laser output.
(2) user can adjust the ratio between output modulated current and the output offset electric current, to adapt to the characteristic of different laser device through different resistance values is set.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is made further detailed description.
Referring to shown in Figure 2; The optical communication laser driver modulated current proportional compensation circuit that the embodiment of the invention provides; First current mirror that comprises reference current source Iref, constitutes by transistor M1, M2, M3, the current ratio amplifier that constitutes by amplifier AMP1, resistance R 1, R2, second current mirror and modulated current output module MODout and the bias current output module BIASout that constitute by transistor M4, M5; Wherein
Reference current source Iref is used to provide current reference;
First current mirror links to each other with reference current source Iref, current ratio amplifier and bias current output module BIASout respectively, is used for the reference current of reference current source Iref output is mirrored to bias current output module BIASout and current ratio amplifier respectively;
The current ratio amplifier is connected between first current mirror and second current mirror, is used for current compensation, outputs to second current mirror after the current signal amplification with the output of first current mirror;
Second current mirror also links to each other with modulated current output module MODout, is used for the current controling signal after amplifying is outputed to modulated current output module MODout;
Modulated current output module MODout is used for the current controling signal according to the input of second current mirror, will convert modulated current signal into by the modulation signal of signal end input, and modulated current signal is outputed to semiconductor laser;
Bias current output module BIASout is used for generating bias current signal according to the current signal of first current mirror input, and bias current signal is outputed to semiconductor laser.
The circuit of the embodiment of the invention is realized describing in detail as follows:
Referring to shown in Figure 2, first current mirror is made up of transistor M1, M2 and M3, and the grid of transistor M1, M2 and M3 links to each other; The grid of transistor M1 links to each other with drain electrode; Also link to each other with the end of reference current source Iref, the other end ground connection of reference current source Iref, the drain electrode of transistor M2 links to each other with bias current output module BIASout; The drain electrode of transistor M3 links to each other with the current ratio amplifier, and the source electrode of transistor M1, M2 and M3 connects power supply.
The current ratio amplifier is made up of amplifier AMP1, resistance R 1 and R2; The inverting input INN of amplifier AMP1 links to each other with the drain electrode of transistor M3 and an end of resistance R 1 respectively; In-phase input end INP links to each other with an end of second current mirror and resistance R 2 respectively; Output OUT links to each other with second current mirror, the equal ground connection of the other end of resistance R 1 and R2.
Second current mirror is made up of transistor M4 and M5; The grid of transistor M4 and M5 links to each other with the output OUT of amplifier AMP1; The drain electrode of transistor M4 links to each other with the in-phase input end INP of amplifier AMP1; The drain electrode of transistor M5 links to each other with modulated current output module MODout, and the source electrode of transistor M4 and M5 connects power supply.
Modulation signal input Dinp and the Dinn of modulated current output module MODout connect 2 road modulating input signals respectively; Current controling end Imodctrl connects the drain electrode of transistor M5, and modulated current output Imodout connects the semiconductor laser negative terminal of laser assembly LDPD.
The current controling end Ibiasctrl of bias current output module BIASout links to each other with the drain electrode of transistor M2, and bias current output Ibiasout connects the semiconductor laser negative terminal of laser assembly LDPD.
The principle of the embodiment of the invention is set forth as follows in detail:
First current mirror that transistor M1, M2 and M3 constitute is used for current mirror control, and the reference current that will come from the reference current Iref of unit is mirrored to bias current output module BIASout and amplifier AMP1 respectively through transistor M2 and M3.Second current mirror that transistor M4 and M5 constitute also is used for current mirror control, and the current controling signal after current ratio is amplified outputs to modulated current output module MODout.The current ratio amplifier that amplifier AMP1, resistance R 1 and R2 constitute is used for current compensation, behind the current signal amplification several times with transistor M3 output, outputs to second current mirror that is made up of transistor M4 and M5 through the OUT mouth.
Modulated current output module MODout receives the current controling signal that second current mirror is exported through current controling end Imodctrl, will be converted into a certain size modulated current signal by the modulation signal of signal end Dinp and Dinn input, from the output of Imodout end.Bias current output module BIASout receives the current signal that first current mirror is exported through current controling end Ibiasctrl, generates a certain size bias current signal, from the output of Ibiasout end.
The electric current that let flow is crossed transistor M3 drain electrode is Im3, and then the voltage Vr1 on the resistance R 1 is Vr1=Im3*R1.When amplifier AMP1 is in normal operating conditions; Because amplifier AMP1 reaches the characteristic of balance, the input INN of amplifier AMP1 and the current potential of INP should equate, thereby the voltage Vr2 on the resistance R 2 equates with voltage Vr1 on the resistance R 1; Vr1=Vr2; So flow through the electric current I m4 of transistor M4 with the electric current I m3 that flows through transistor M3 drain electrode between relation be: Im3*R1=Im4*R2, i.e. Im3/Im4=R2/R1, thereby realized the current ratio amplification that is provided with by resistance.
The electric current output multiplication factor of supposing modulated current output module MODout is Am, and the electric current output multiplication factor of bias current output module BIASout is Ab, and the mirror-image property of the current mirror that transistor M1, M2, M3 constitute is 1: 1: 1; The mirror-image property of the current mirror that transistor M4, M5 constitute is 1: 1, and then the big or small Ibiasout of the bias current of output is:
Ibiasout=Im2*Ab
=Iref*Ab
And the big or small Imodout of the modulated current of output is:
Imodout=Im5*Am
=Im4*Am
=R1/R2*Im3*Am
=R1/R2*Iref*Am
Therefore, the proportionate relationship T between output modulated current and the output offset electric current can be expressed as:
T=Imodout/Ibiasout
=(R1/R2*Iref*Am)/(Iref*Ab)
=R1/R2*Am/Ab
Because in the following formula, Am and Ab be respectively the output modulation module in the output offset module intrinsic output amplification characteristic, and resistance R 1 can be set by the user with R2, thereby has realized the ratio amplification that can be provided with between output modulated current and the output offset electric current.
Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, belong within the scope of claim of the present invention and equivalent technologies thereof if of the present invention these are revised with modification, then the present invention also is intended to comprise these changes and modification interior.
The content of not doing in this specification to describe in detail belongs to this area professional and technical personnel's known prior art.