CN117080860A - Modulation current control circuit and data transmission circuit - Google Patents
Modulation current control circuit and data transmission circuit Download PDFInfo
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- H—ELECTRICITY
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- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0427—Electrical excitation ; Circuits therefor for applying modulation to the laser
Abstract
The application provides a modulation current control circuit and a data transmission circuit, wherein the modulation current control circuit comprises: the laser, the loop control circuit and the driving circuit are connected in pairs; the laser converts the current luminous intensity into monitoring current in real time through a backlight monitoring diode of the laser and inputs the monitoring current into a loop control circuit; the loop control circuit is used for comparing the amplitude of the monitoring current with the amplitude of the reference current so as to output a voltage control signal to the driving circuit; and the driving circuit is used for controlling and outputting a target modulation current according to the voltage modulation signal and the voltage control signal so as to continuously act on the laser. The application can reasonably and circularly control the modulation current of the laser through the loop control circuit and the driving circuit so as to ensure better extinction ratio and reduce the data transmission error rate.
Description
Technical Field
The present application relates to the field of circuit technologies, and in particular, to a modulation current control circuit and a data transmission circuit.
Background
In high-speed optical communications applications, the data stream is transmitted along a physical medium such as an optical fiber by converting an electrical signal into an optical signal using a laser driving circuit. The extinction ratio is a key index of the luminous performance of the laser and is used for measuring the distinguishing degree of 1 light pulse and 0 light pulse sent out by the laser; the extinction ratio is required to be large enough to enable a receiving end chip at the downstream of the optical fiber transmission to obtain a low enough error rate; and the modulation current of the laser is the key for adjusting the extinction ratio of the optical signal. The conventional laser driving circuit generally sets a fixed modulation current, so that the light emitting efficiency of the laser is greatly affected along with the change of environmental factors such as temperature, and therefore error codes are easy to generate, and the problems of packet loss of data streams and the like are caused.
Disclosure of Invention
The application aims to provide a modulation current control circuit and a data transmission circuit, which can reasonably and circularly control the current modulation current of a laser through a loop control circuit and a driving circuit so as to ensure better extinction ratio and reduce data transmission error rate.
In a first aspect, the present application provides a modulation current control circuit comprising: the laser, the loop control circuit and the driving circuit are connected in pairs; the laser converts the current luminous intensity into monitoring current in real time through a backlight monitoring diode of the laser and inputs the monitoring current into a loop control circuit; the loop control circuit is used for comparing the amplitude of the monitoring current with the amplitude of the reference current so as to output a voltage control signal to the driving circuit; and the driving circuit is used for controlling and outputting a target modulation current according to the voltage modulation signal and the voltage control signal so as to continuously act on the laser.
Further, the loop control circuit includes: a reference current generating circuit, a first current amplitude detecting circuit, a second current amplitude detecting circuit and a differential difference amplifier; the reference current generating circuit is connected with the second current amplitude detecting circuit; the first current amplitude detection circuit and the second current amplitude detection circuit are respectively connected with the differential difference amplifier; the reference current generating circuit is used for outputting a reference current to the second current amplitude detecting circuit according to the input voltage modulation signal and the preset control signal; the first current amplitude detection circuit is used for extracting a first complementary differential current amplitude signal in the monitoring current and inputting the first complementary differential current amplitude signal to the differential difference amplifier; the second current amplitude detection circuit is used for extracting a complementary second differential current amplitude signal in the reference current and inputting the complementary second differential current amplitude signal to the differential difference amplifier; and the differential difference amplifier is used for outputting a voltage control signal according to the first differential current amplitude signal and the second differential current amplitude signal which are complementary.
Further, the reference current generating circuit includes: a first controllable current source and a first switch connected in series; the first controllable current source is used for outputting reference current according to a preset control signal; and the first switch is used for controlling the output of the reference current according to the voltage modulation signal.
Further, the preset control signal is determined based on the magnitude of the modulation current required by the laser and the proportional relationship between the laser and the corresponding backlight monitor diode.
Further, the first current amplitude detection circuit and the second current amplitude detection circuit each include: the current-voltage conversion circuit, the first amplifier, the high-pass filter, the differential pair amplifier, the rectifier and the low-pass filter are connected in sequence; a current-voltage conversion circuit for converting an input current signal into a first voltage signal; the first amplifier is used for performing first gain amplification processing on the first voltage signal and outputting a second voltage signal; the high-pass filter is used for performing first filtering processing on the second voltage signal and outputting a third voltage signal; the differential pair amplifier is used for carrying out second gain amplification processing on the third voltage signal according to the common-mode voltage signal and outputting a complementary first differential signal; the rectifier is used for extracting the amplitude information of the complementary first differential signal and converting the amplitude information into a complementary second differential signal; and the low-pass filter is used for carrying out second filtering processing on the complementary second differential signals and outputting complementary third differential signals.
Further, the current-voltage conversion circuit is of a TIA transimpedance amplifier structure; the TIA transimpedance amplifier structure includes an inverting amplifier and a resistor in parallel relationship.
Further, the rectifier is a gilbert cell circuit.
Further, the low-pass filter is an integrator type circuit.
Further, the driving circuit includes: a second controllable current source and a second switch connected in series; the other end of the second switch is connected with a laser; the second controllable current source is used for outputting a target modulation current according to the voltage control signal so as to continuously act on the laser; and a second switch for controlling the output of the target modulation current according to the voltage modulation signal.
In a second aspect, the present application also provides a data transmission circuit comprising a modulated current control circuit as described in the first aspect.
In the modulation current control circuit and the data transmission circuit provided by the application, the modulation current control circuit comprises: the laser, the loop control circuit and the driving circuit are connected in pairs; the laser converts the current luminous intensity into monitoring current in real time through a backlight monitoring diode of the laser and inputs the monitoring current into a loop control circuit; the loop control circuit is used for comparing the amplitude of the monitoring current with the amplitude of the reference current so as to output a voltage control signal to the driving circuit; and the driving circuit is used for controlling and outputting a target modulation current according to the voltage modulation signal and the voltage control signal so as to continuously act on the laser. In the mode, the modulation current of the laser can be reasonably and circularly controlled through the loop control circuit and the driving circuit, so that a good extinction ratio is ensured, and the data transmission error rate is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present application, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a related art laser-based data transmission;
fig. 2 is a diagram showing a conventional laser driving circuit in the related art;
FIG. 3 is a block diagram of a modulation current control circuit according to an embodiment of the present application;
fig. 4 is a circuit diagram of a modulation current control circuit according to an embodiment of the present application;
fig. 5 is a block diagram of a loop control circuit according to an embodiment of the present application;
FIG. 6 is a circuit diagram of a reference current generating circuit according to an embodiment of the present application;
fig. 7 is a block diagram of the overall structure of a loop control circuit according to an embodiment of the present application;
fig. 8 is a circuit diagram of two current-voltage conversion circuits according to an embodiment of the present application;
fig. 9 is a circuit diagram of a first amplifier circuit according to an embodiment of the present application;
fig. 10 is a circuit diagram of a high-pass filter according to an embodiment of the present application;
fig. 11 is a circuit diagram of a differential pair amplifier according to an embodiment of the present application;
fig. 12 is a circuit diagram of a rectifier according to an embodiment of the present application;
fig. 13 is a circuit diagram of a low-pass filter according to an embodiment of the present application;
fig. 14 is a circuit diagram of a differential amplifier according to an embodiment of the present application;
fig. 15 is a circuit diagram of a driving circuit according to an embodiment of the present application;
fig. 16 is an equivalent circuit diagram of a modulation current control circuit according to an embodiment of the present application.
Detailed Description
The technical solutions of the present application will be clearly and completely described in connection with the embodiments, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
As shown in fig. 1, DATA is a DATA stream to be transmitted, that is, a voltage modulation signal, which is a sequence code of 1001001010000101010. Driver1 is a driving circuit of the laser, LD is the laser, VDD is the operating voltage of the laser, and is typically 3.3V. IMOD is the modulation current of the laser. When data 1 is transmitted, the luminous intensity of the laser is high; at the time of transmitting data "0", the light emission intensity of the laser is weak. By means of this "coding" of strong and weak light, the transmission of the optical signal stream is achieved.
The Extinction Ratio (ER) is a key indicator of the light emission performance of a laser, and is used to measure the degree of distinction between a "1" light pulse and a "0" light pulse sent out by the laser. Let P1 be the optical power of the "1" light pulse, and P0 be the optical power of the "0" light pulse, the extinction ratio is defined as 10lg (P1/P0). The extinction ratio is required to be sufficiently high to achieve a sufficiently low bit error rate for the receiving end chip downstream of the optical fiber transmission. The extinction ratio cannot be too large, so that optical signals generated on the laser are easy to generate optical surges and oscillations, and the problems of error codes and the like are also caused. Therefore, in order to achieve high quality optical signal transmission, the extinction ratio is set at an appropriate value.
IMOD is used as the modulation current of a laser, and the larger the current is, the larger the intensity and the weak distinction of the light emitted by the laser is. Therefore, setting a reasonable IMOD size is key to adjusting the extinction ratio of the optical signal. Conventional laser driving circuits will set a fixed modulation current IMOD as shown in fig. 2. Imoddac is a constant current source with fixed bias, SW1 is a high-speed switch. DATA is the signal to be transmitted. DATA acts directly on SW 1. If data= "1", SW1 is closed, the Imoddac current can turn on and illuminate the laser, which operates in a "strong" light state. If data= "0", SW1 is off, imoddac current cannot pass out, and the laser operates in a "weak" light state.
Such a drive circuit is capable of coping with laser driving in a typical application. However, as environmental factors, particularly temperature, change, the light emission efficiency of the laser is greatly affected. For example, at high temperatures, the light emission efficiency of the laser decreases and the threshold current increases. If a fixed modulation current is set as Imoddac, the extinction ratio is greatly reduced compared with the light emission at normal temperature under a high-temperature environment, and error codes are easy to generate, so that data stream packet loss is caused. Also, the light emission efficiency of the laser is greatly improved and the threshold current is reduced at a low temperature as compared with the normal temperature. If the same modulation current is kept at Imoddac at low temperature, the extinction device is oversized, and problems such as light surge and high error rate are caused.
Based on this, the embodiment of the application provides a modulation current control circuit and a data transmission circuit, which can reasonably control the current modulation current of a laser through a loop control circuit and a driving circuit so as to ensure a better extinction ratio and reduce the data transmission error rate.
Fig. 3 is a block diagram of a modulation current control circuit according to an embodiment of the present application, where the modulation current control circuit includes: the laser 11, the loop control circuit 12 and the driving circuit 13 are connected in pairs; the laser 11 converts the current luminous intensity into a monitoring current in real time through a backlight monitoring diode 111 of the laser and inputs the monitoring current into a loop control circuit 12; a loop control circuit 12 for comparing the magnitude of the monitor current with the magnitude of the reference current to output a voltage control signal to the driving circuit 13; the driving circuit 13 is used for controlling and outputting a target modulation current according to the voltage modulation signal and the voltage control signal so as to adjust the luminous intensity of the laser.
Referring to a specific circuit structure of the modulation current control circuit shown in fig. 4, LD is a laser. The MPD is a backlight monitoring diode of the laser and a photosensitive device working in a reverse bias voltage state, so that the current luminous intensity of the laser is converted into monitoring current, namely IMPD in real time. Imod_ctrl is a loop control circuit that samples the IMPD current signal and outputs an imod_regulated voltage control signal by sampling and comparison of the feedback loop. The imod_regulation voltage control signal is sent to the Driver2 module to adjust the IMOD. Driver2 is a laser driving circuit, modulates the DATA signal into a current signal, and drives the laser to emit optical signals of "1" and "0". I.e. the laser is operated in continuous mode or in burst mode with short guard time. The guard time refers to a time slot in which the laser emits light, i.e., a period of time during which no light is emitted, in the burst mode.
Compared with the conventional mode of setting fixed IMOD, the modulation current control circuit provided by the embodiment of the application automatically adjusts the modulation current IMOD of the laser by detecting the current amplitude of the IMPD monitoring current. Environmental factors, such as changes in laser temperature, can lead to changes in parameters of the laser itself, such as threshold current and luminous efficiency, and thus to deviations in luminous intensity. But MPD is a photosensitive device and the conversion efficiency of light intensity to monitor current IMPD is not substantially changed. By comparing the IMPD current with a precise reference quantity which does not change with the environment, the negative feedback loop automatically adjusts the IMOD, so that the light-emitting deviation of the laser is corrected, the high-quality transmission of the optical link is realized, and the robustness is stronger.
The reference current in the loop control circuit is generated according to a preset control signal, and the preset control signal is determined based on the magnitude of the modulation current required by the laser and the current proportional relationship between the laser and the corresponding backlight monitoring diode. The loop control circuit can continuously output a voltage control signal for adjusting the current modulation current of the laser in real time, the voltage control signal acts on the driving circuit, so that the driving circuit can output the adjusted target modulation current to act on the laser until the output target modulation current reaches the modulation current required by the laser, and the circuit is in a stable state so as to ensure the high-quality optical link transmission of the laser and reduce the data transmission error rate.
The embodiment of the present application further provides a modulation current control circuit, referring to fig. 5, the loop control circuit 12 includes: a reference current generation circuit 121, a first current amplitude detection circuit 122, a second current amplitude detection circuit 123, and a differential difference amplifier 124; the reference current generation circuit 121 is connected to the second current amplitude detection circuit 123; the first current amplitude detection circuit 122 and the second current amplitude detection circuit 123 are connected to a differential difference amplifier 124, respectively.
A reference current generating circuit 121 for outputting a reference current to the second current amplitude detecting circuit 123 according to the inputted voltage modulation signal and a preset control signal; a first current amplitude detection circuit 122 for extracting a complementary first differential current amplitude signal in the monitor current, and inputting the signal to a differential difference amplifier 124; a second current amplitude detection circuit 123 for extracting a complementary second differential current amplitude signal in the reference current, and inputting the signal to a differential difference amplifier 124; the differential difference amplifier 124 is configured to output a voltage control signal according to the first differential current amplitude signal and the second differential current amplitude signal which are complementary.
The reference current generation circuit 121 includes: a first controllable current source and a first switch connected in series; the first controllable current source is used for outputting reference current according to a preset control signal; and the first switch is used for controlling the output of the reference current according to the voltage modulation signal. The specific circuit configuration is shown in fig. 6, and a static adjustable current is chopped into an alternating current by using a voltage modulation signal DATA of a laser. SW2 is a switch controlled by the DATA voltage modulation signal. When data=1, SW2 is closed and current flows. When data=0, SW2 is turned off, and the output current is 0. The output current Iref AC has a magnitude Iref DC. The magnitude of Iref_DC is determined by the preset control signal IMPD_AC_TARGET [3:0], monotonically and linearly.
The preset control signal is determined based on the magnitude of the modulation current required by the laser and the current proportional relationship between the laser and the corresponding backlight monitor diode, for example, the modulation current required by the laser is 40mA, and the current proportional relationship between the laser and the corresponding backlight monitor diode is 100:1, the preset control signal should be a control signal for generating a reference current of 0.4mA, which may be a four-bit digital control signal for a control word.
Further, the first current amplitude detection circuit 122 and the second current amplitude detection circuit 123 each include: the current-voltage conversion circuit, the first amplifier, the high-pass filter, the differential pair amplifier, the rectifier and the low-pass filter are connected in sequence; a current-voltage conversion circuit for converting an input current signal into a first voltage signal; the first amplifier is used for performing first gain amplification processing on the first voltage signal and outputting a second voltage signal; the high-pass filter is used for performing first filtering processing on the second voltage signal and outputting a third voltage signal; the differential pair amplifier is used for carrying out second gain amplification processing on the third voltage signal according to the common-mode voltage signal and outputting a complementary first differential signal; the rectifier is used for extracting the amplitude information of the complementary first differential signal and converting the amplitude information into a complementary second differential signal; and the low-pass filter is used for carrying out second filtering processing on the complementary second differential signals and outputting complementary third differential signals.
Referring to the overall circuit diagram of the loop control circuit 12 (i.e., the IMPD _ CTRL module) shown in fig. 7; the reference current generating circuit 121 is a ref_gen module in the drawing. The first current amplitude detection circuit 122 includes: I2V1, AMP1, HPF1, AMP2, REC1, LPF1; the second current amplitude detection circuit 123 includes: I2V2, AMP3, HPF2, AMP4, REC2, LPF2; the differential difference amplifier 124 is an AMP5 block.
The I2V1 input signal is connected to the IMPD current and the output is connected to the voltage signal VMPD. The input signal of AMP1 is connected with VMPD, and the output is connected with VO1. The input signal of the HPF1 module is connected with VO1, and the output signal is connected with VO2. The input signal of AMP2 is connected to VO2 and common mode voltage signal VCM1, and the output signals are connected to VO3P and VO3N. The REC1 module inputs signals to VO3P and VO3N, and outputs signals to VO4P and VO4N. The input signal of the LPF1 module is connected with VO4P and VO4N, and the output signal is connected with VO5P and VO5N. The input signal of REF_GEN module is connected with voltage modulation signal DATA and preset control signal IMPD_AC_TARGET [3:0], and outputs current signal Iref_AC. The input signal of the I2V2 module is connected with Iref_AC, and the output signal is connected with Vref. The input signal of AMP3 is connected with Vref, and the output signal is connected with VO6. The input signal of the HPF2 module is connected with VO6, and the output signal is connected with VO7. The input signal of the AMP4 block is connected to VO7 and the common mode voltage signal VCM2, and the output signal is connected to VO8P and VO8N. The input signal of the REC2 module is connected with VO8P and VO8N, and the output signal is connected with VO9P and VO9N. The input signal of the LPF2 module is connected with VO9P and VO9N, and the output signal is connected with VO10P and VO10N. The input signal of the AMP5 module is connected with V5P, V5N, V P and V10N, and the output signal is connected with imod_regulation voltage control signal.
The I2V1 and I2V2 blocks in fig. 7 are current-to-voltage conversion circuits, which act as a transimpedance amplifier to convert a current input signal into a voltage signal. The input signal of the I2V1 module is connected to MPD current, IMPD and the output signal is connected to amplifier AMP 1. The input signal of the I2V2 block is coupled to the output current signal iref_ac of ref_gen and the output signal is coupled to the amplifier AMP2.
The implementation of I2V1 and I2V2 may be as shown in fig. 8 (a) or fig. 8 (b). In the circuit of fig. 8 (a), iin is the input current signal, R1 is a resistor to ground, and vout is the converted voltage output signal. In the circuit of fig. 8 (b), R2 is a resistor, and is connected to the input current signal Iin and the voltage output signal vout, respectively. AMP6 is an inverting amplifier that receives the input current signal Iin and the voltage output signal vout. R2 and AMP6 together form a typical TIA transimpedance amplifier structure. The structure of fig. 8 (b) has a higher bandwidth due to the low input impedance characteristic of the TIA transimpedance amplifier, which is more suitable for the present solution design.
AMP1 and AMP3 are amplifiers of the same circuit, and realize gain amplification of VMPD and Vref, respectively. The circuit structure is shown in fig. 9. Wherein M1 is an NMOSFET with a grounded source, R3 is a resistor, and M1 and R3 form a common source amplifier. vin1 is the input signal of the amplifier and vout1 is the output signal. VDD is the supply voltage. Further, the current-voltage conversion circuit is of a TIA transimpedance amplifier structure; the TIA transimpedance amplifier structure includes an inverting amplifier and a resistor in parallel relationship.
HPF1 and HPF2 are high pass filters of the same circuit. The HPF1 is used for filtering the direct current part of the IMPD after the average current flows through the I2V1, and only alternating current and amplitude signal components are reserved. The HPF2 is used for filtering the direct current part of the Iref_AC average current after the I2V2 flows, and only alternating current and amplitude signal components are reserved. The circuit is shown in fig. 10. Wherein vin2 is the input port signal of the high pass filter, and vout2 is the output port signal. C1 is the filter capacitance and R4 is the filter resistance. vcm is a bias voltage signal that biases the next stage amplifiers AMP2 and AMP4 at a suitable input common mode voltage so that AMP2 and AMP4 operate at a suitable input voltage range.
AMP2 and AMP4 are amplifiers of the same circuit, and realize gain amplification of the high-pass filter output signal. A conventional differential pair amplifier implementation may be employed as shown in fig. 11. M3 and M4 are input differential pair NMOS, R5 and R6 are load resistors, and C2 is output filter capacitor for filtering edge burr of output end. IB1 is the tail current source of the amplifier, providing the bias current for the amplifier. vin3 is the output voltage signal of the upper high pass filter HPF. vcm is the output bias voltage of the upper stage high pass filter HPF. vout+ and vout-are differential output voltage signals.
REC1 and REC2 are rectifier circuits of the same circuit. The method is used for extracting the amplitude information of the differential output voltage signal of the upper-stage differential pair amplifier and converting the differential output amplitude into direct current voltage. The circuit is shown in fig. 12 as a typical gilbert cell circuit. M5-M10 are composed of NMOS as the transconductance circuit of the rectifier. IB2 is a bias current source. R7-R8 are load resistors. C3 is an output filter capacitor for stabilizing and filtering the direct current output differential voltage.
The differential output voltage amplitude of the rectifier is related to the amplitude of the input signal as follows:
where DeltaVout 4 is the voltage difference between vout4+ and vout4-, deltavin 4 is the voltage difference between vin4+ and vin 4-. K is the gain factor.
LPF1 and LPF2 are low-pass filter circuits of the same circuit for filtering high-frequency ripple on the output signal of the previous stage rectifier, and only low-frequency components are retained. The circuit is shown in fig. 13, in the form of an integrator implementation. The integrator has a low frequency pole low enough, determined by the resistance and capacitance. The pole is used as the main pole point of the whole negative feedback loop, and determines the stability of the negative feedback loop. Dominant pole frequency w0=1/R9C4; r9=r10, c4=c5; OPA is an operational amplifier.
AMP5 is a differential amplifier, DDA. The differential amplification function between the difference value of VO5P-VO5N and the difference value of VO10P-VO10N in the figure 7 is realized. The circuit implementation is shown in fig. 14. va+ and va-are a set of differential input signals; vb+ and vb-are another set of differential input signals. vbiasp1, vbiasn1 and vbian2 are voltage bias signals M15-M18 are PMOS of the same size and transconductance is gmp. Let Deltava be the voltage difference between va+ and va-, deltavb be the voltage difference between vb+ and vb-, then:
；
；
vout6 is the output voltage of the DDA amplifier. Let the output impedance be rout6, then:
；
replacing each sub-module in the block diagram of fig. 7 with each sub-module circuit of fig. 6-14 results in a complete implementation of imod_ctrl.
When the modulation current IMOD on the laser increases > AC current of IMPD increases > amplitude of VMPD increases > amplitude of VO1 increases > amplitude of VO2 increases > amplitude of VO3P-VO3N increases > amplitude of VO4P-VO4N increases > amplitude of VO5P-VO5N increases > imod_regulation increases.
So far, the first half of the debug current IMOD regulation loop has been implemented.
The driving circuit includes: a second controllable current source and a second switch connected in series; the other end of the second switch is connected with the output end of the laser; the second controllable current source is used for outputting a target modulation current according to the voltage control signal so as to continuously act on the laser; and a second switch for controlling the output of the target modulation current according to the voltage modulation signal. I.e., the Driver2 module in fig. 4 is the second half of the IMOD regulation loop. The static Imoddac shown in fig. 2 is generated using the imod_regulated voltage control signal. The modulation signal DATA is applied to the switch SW1, and an IMOD current signal is output to the laser. The circuit shown in fig. 2 may be implemented with the circuit shown in fig. 15. NMOSM33 is SW1, and when data=1, M33 is turned on, and current flows from IMOD. When data=0, M33 is off, IMOD has no current flowing out, and a current mirror is formed for 0.m30-M31 to mirror the M29 current out. M32 is used for matching with M33, so that the on-resistance of the current mirror is prevented from influencing the mirror proportion of the current mirror. imod_regulation acts on gate of PMOSM29 to effect voltage to current conversion. The larger the imod_regulation voltage, the smaller the channel current of M29.
The second half of IMOD modulation has been achieved so far.
The first half and the second half of the IMOD regulating loop were spliced together to find that:
when the modulation current IMOD on the laser increases- > AC current of IMPD increases- > amplitude of VMPD increases- > amplitude of VO1 increases- > amplitude of VO2 increases- > amplitude of VO3P-VO3N increases- > amplitude of VO4P-VO4N increases- > amplitude of VO5P-VO5N increases- > imod_regulation increases- > current decreases- > IMOD decreases. Forming a complete negative feedback closed loop.
The negative feedback loop compares the AC current amplitude of MPD with the AC current amplitude of REF_GEN, and generates imod_regulation voltage signals through an intermediate-stage amplifier, a filter, a rectifier and a DDA amplifier, so as to control the amplitude of modulating current IMOD on a laser and realize the automatic adjustment of extinction ratio ER. The overall loop schematic is shown in fig. 16. The final loop stabilizes at an AC current amplitude of IMPD equal to the AC current amplitude of REF GEN. According to FIG. 6, the amplitude of the AC current of REF_GEN can be adjusted by adjusting IMPD_AC_TARGET [3:0], and finally the size of IMOD, i.e. the size of the laser optical signal ER, is adjusted.
The modulation current control circuit provided by the embodiment of the application automatically adjusts the modulation current by detecting and monitoring the amplitude of the current. The influence of environmental factors on the parameters of the laser, such as the threshold current and the luminous efficiency, is avoided, and the deviation of the luminous intensity is further caused, so that the extinction ratio is influenced. In the embodiment of the application, since the MPD is a photosensitive device, the conversion efficiency from the light intensity to the monitoring current IMPD is basically unchanged. Therefore, by comparing the IMPD current with a precise reference quantity which does not change along with the environment, the negative feedback loop automatically adjusts the IMOD, so that the light-emitting deviation of the laser is corrected, the high-quality transmission of the optical link is realized, and the robustness is stronger.
Based on the embodiment of the modulation current control circuit, the application further provides a data transmission circuit, and the data transmission circuit comprises the modulation current control circuit.
The implementation principle and the technical effects of the data transmission circuit provided by the embodiment of the application are the same as those of the embodiment of the modulation current control circuit, and for the sake of brevity, reference may be made to the corresponding content in the embodiment of the modulation current control circuit.
In the description of the present application, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Finally, it should be noted that: the above examples are only specific embodiments of the present application, and are not intended to limit the scope of the present application, but it should be understood by those skilled in the art that the present application is not limited thereto, and that the present application is described in detail with reference to the foregoing examples: any person skilled in the art may modify or easily conceive of the technical solution described in the foregoing embodiments, or perform equivalent substitution of some of the technical features, while remaining within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A modulated current control circuit, the modulated current control circuit comprising: the laser, the loop control circuit and the driving circuit are connected in pairs;
the laser converts the current luminous intensity into monitoring current in real time through a backlight monitoring diode of the laser and inputs the monitoring current into the loop control circuit;
the loop control circuit is used for comparing the amplitude of the monitoring current with the amplitude of the reference current so as to output a voltage control signal to the driving circuit;
the driving circuit is used for controlling and outputting a target modulation current according to the voltage modulation signal and the voltage control signal so as to continuously act on the laser.
2. The modulation current control circuit according to claim 1, wherein the loop control circuit comprises: a reference current generating circuit, a first current amplitude detecting circuit, a second current amplitude detecting circuit and a differential difference amplifier;
the reference current generating circuit is connected with the second current amplitude detecting circuit; the first current amplitude detection circuit and the second current amplitude detection circuit are respectively connected with the differential difference amplifier;
the reference current generating circuit is used for outputting a reference current to the second current amplitude detecting circuit according to the input voltage modulation signal and a preset control signal;
the first current amplitude detection circuit is used for extracting a first complementary differential current amplitude signal in the monitoring current and inputting the first complementary differential current amplitude signal to the differential difference amplifier;
the second current amplitude detection circuit is used for extracting a complementary second differential current amplitude signal in the reference current and inputting the signal to the differential difference amplifier;
the differential difference amplifier is used for outputting a voltage control signal according to the first differential current amplitude signal and the second differential current amplitude signal which are complementary.
3. The modulation current control circuit according to claim 2, wherein the reference current generation circuit comprises: a first controllable current source and a first switch connected in series;
the first controllable current source is used for outputting reference current according to the preset control signal;
the first switch is used for controlling the output of the reference current according to the voltage modulation signal.
4. A modulated current control circuit according to claim 3, characterized in that the preset control signal is determined based on the magnitude of the modulated current required by the laser and the current proportional relationship between the laser and the corresponding backlight monitor diode.
5. The modulated current control circuit of claim 2 wherein said first current magnitude detection circuit and said second current magnitude detection circuit each comprise: the current-voltage conversion circuit, the first amplifier, the high-pass filter, the differential pair amplifier, the rectifier and the low-pass filter are connected in sequence;
the current-voltage conversion circuit is used for converting an input current signal into a first voltage signal;
the first amplifier is used for performing first gain amplification processing on the first voltage signal and outputting a second voltage signal;
the high-pass filter is used for performing first filtering processing on the second voltage signal and outputting a third voltage signal;
the differential pair amplifier is used for performing second gain amplification processing on the third voltage signal according to a common-mode voltage signal and outputting a complementary first differential signal;
the rectifier is used for extracting the amplitude information of the complementary first differential signal and converting the amplitude information into a complementary second differential signal;
and the low-pass filter is used for carrying out second filtering processing on the complementary second differential signals and outputting complementary third differential signals.
6. The modulated current control circuit of claim 5, wherein the current to voltage conversion circuit is a TIA transimpedance amplifier structure; the TIA transimpedance amplifier structure includes an inverting amplifier and a resistor in parallel relationship.
7. The modulated current control circuit of claim 5 wherein the rectifier is a gilbert cell circuit.
8. The modulated current control circuit of claim 5 wherein said low pass filter is an integrator form circuit.
9. The modulation current control circuit according to claim 1, wherein the driving circuit comprises: a second controllable current source and a second switch connected in series; the other end of the second switch is connected with the laser;
the second controllable current source is used for outputting a target modulation current according to the voltage control signal so as to continuously act on the laser;
the second switch is used for controlling the output of the target modulation current according to the voltage modulation signal.
10. A data transmission circuit comprising a modulated current control circuit as claimed in any one of claims 1 to 9.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117420479A (en) * | 2023-12-19 | 2024-01-19 | 成都光创联科技有限公司 | Negative bias current testing circuit for backlight detector of common-negative optical device |
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Address after: 9/F, Block A, No. 333 Dehua Road, Gaoxin District, Chengdu, Sichuan, 610000 Patentee after: Chengdu Mingyi Electronic Technology Co.,Ltd. Guo jiahuodiqu after: Zhong Guo Address before: 9/F, Block A, No. 333 Dehua Road, Gaoxin District, Chengdu, Sichuan, 610000 Patentee before: Chengdu Mingyi Electronic Technology Co.,Ltd. Guo jiahuodiqu before: Zhong Guo |