CN115296141A - VCSEL laser current bias circuit and control method thereof - Google Patents
VCSEL laser current bias circuit and control method thereof Download PDFInfo
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Abstract
The invention provides a VCSEL laser current bias circuit and a control method thereof, belonging to the field of optical communication. The control idea is as follows: setting the closed-loop bandwidth of the laser current bias circuit to be lower than the low-frequency cut-off frequency of the laser driver, connecting the output end of the laser current bias circuit with the laser driver, and enabling the output end to be provided with a signal from the laser driver at the moment; when the frequency of a signal from a laser driver on an output end is lower than the closed-loop bandwidth of a laser current bias circuit, the laser current bias circuit is used as a current source generation unit, and the output end outputs high impedance; when the frequency of the signal from the laser driver on the output end is higher than the closed-loop bandwidth of the laser current bias circuit, the laser current bias circuit is converted into a voltage source generation unit, and the output end outputs low impedance; the invention provides high-precision wide-range bias current for the laser through the output end, and has the characteristics of low impedance, self-adaption to the bias voltage of the laser and no influence on the low-frequency cut-off frequency and bandwidth of the laser driver.
Description
Technical Field
The invention relates to a VCSEL laser current bias circuit and a control method thereof, belonging to the technical field of circuits.
Background
In the field of optical communications, a VCSEL laser is a common laser used for short-distance transmission of information. Currently common VCSEL laser drivers are classified into cathode modulation laser drivers and anode modulation laser drivers. The cathode modulation laser driver connects the cathode of the laser with the output end of the laser driver, and the anode of the laser is connected with the power supply. The cathode modulation laser driver system needs to provide two sets of power supplies with different voltages, the power supply with lower voltage provides voltage for the laser driver, and the power supply with higher voltage provides voltage for the laser anode, so that the design complexity of the laser driver power supply system and the power consumption of the laser driver system are increased. The anode modulation laser driver connects the anode of the laser with the output end of the laser driver, and the cathode of the laser is grounded, so that the complexity of the design of a power supply system is reduced, and the power consumption of the system is reduced. Therefore, the design of the VCSEL laser current bias circuit applied to anode modulation is of great significance.
In the prior art, the bias current flowing through the laser is adjusted by adjusting the current of the current source. Disadvantages of such a laser bias circuit include: firstly, the parasitic capacitance of the current source greatly reduces the bandwidth of the laser driver, although the influence of partial parasitic capacitance can be eliminated through the large inductance, the effect is still not ideal, and meanwhile, the chip area is also increased for eliminating the large inductance introduced by the parasitic capacitance; and secondly, a high low-frequency cut-off point is introduced into the blocking capacitor, so that the small signal gain characteristic of the laser driver has very low gain at a low frequency band, and the direct current drift problem of the optical fiber system is aggravated.
It is also used that the bias current flowing through the VCSEL laser is equal to the current flowing through resistor R1 minus the drain current flowing through the MOS transistor. The bias current flowing through the laser is adjusted by adjusting the voltage level of the power supply. Although the biasing scheme does not exacerbate the dc drift problem for fiber optic systems, there are disadvantages, including: firstly, adjusting the voltage of the power supply increases the complexity of the power supply of the system outside the driver chip; secondly, the voltage of the power supply is adjusted to obtain the variation trend of the laser bias current, and the specific value of the laser bias current cannot be confirmed.
In conclusion, it is of great significance to design a VCSEL laser current bias circuit.
Disclosure of Invention
The purpose of the invention is as follows:
the invention provides a VCSEL laser current bias circuit and a control method thereof, aiming at providing wide-range high-precision bias current for a VCSEL laser without influencing the low-frequency cut-off frequency and bandwidth of a laser driver circuit.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a VCSEL laser current bias circuit, comprising: the voltage-controlled power supply comprises a first voltage-controlled current source, a clamping unit, a reference load unit and a voltage source generating unit; the reference load unit is provided with a reference current interface Iref; the voltage source generating unit is provided with a second voltage-controlled current source and an output end Iout;
the first voltage-controlled current source and the second voltage-controlled current source are respectively provided with a voltage input end and a current output end, the voltage input end of the first voltage-controlled current source is connected with the voltage input end of the second voltage-controlled current source, and the current output end of the second voltage-controlled current source is connected with the output end Iout; the output end Iout is used for outputting bias current for the laser;
the clamping unit is connected with the first voltage-controlled current source and the voltage source generating unit and is used for enabling the current output end voltage of the first voltage-controlled current source to be equal to the current output end voltage of the second voltage-controlled current source;
the reference load unit is respectively connected with the clamping unit and the voltage source generating unit;
the output end Iout is connected with the laser driver, receives a signal of the laser driver, compares the frequency of the received signal of the laser driver with the closed-loop bandwidth of the laser current bias circuit, and controls the output end Iout to output high impedance or low impedance.
Further, the clamping unit comprises a first clamping circuit, a first voltage division circuit and a third error amplifier; the first end of the first voltage division circuit is used for sampling the voltage of the current output end of the first voltage-controlled current source, the second end of the first voltage division circuit is used for transmitting the voltage signal of the current output end of the first voltage-controlled current source sampled by the first end to the inverting input end of the third error amplifier, and the third end of the first voltage division circuit is connected with the ground; the first end of the first clamping circuit is connected with the current output end of the first voltage-controlled current source, the second end of the first clamping circuit is connected with the output end of the third error amplifier, and the third error amplifier is used for controlling the voltage of the first end of the first clamping circuit through the second end of the first clamping circuit so as to control the voltage of the current output end of the first voltage-controlled current source; the third end of the first clamping circuit is connected with a reference load unit, and the reference load unit samples the current of the first end of the first clamping circuit through the third end of the first clamping circuit, so that the current of the current output end of the first voltage-controlled current source is sampled.
Further, the voltage source generating unit further comprises a second voltage dividing circuit and a first error amplifier; the first end of the second voltage division circuit is used for sampling the voltage of the current output end of the second voltage-controlled current source, and inputting the sampling result to the non-inverting input end of the third error amplifier through the fourth end of the second voltage division circuit; the third end of the second voltage division circuit is connected with the ground.
Further, the reference load unit further includes a second error amplifier, a first reference load, and a second reference load; the first end of the first reference load is connected with the third end of the first clamping circuit and used for sampling the current of the current output end of the first voltage-controlled current source, converting the current into voltage, outputting the voltage to the inverting input end of the second error amplifier through the second end of the first reference load, the second reference load samples the current input through the reference current interface Iref through the first end of the second reference load, converting the current into voltage, outputting the voltage to the non-inverting input end of the second error amplifier through the second end of the second reference load, the second error amplifier is used for comparing the voltages of the non-inverting input end and the inverting input end of the second reference load and outputting the comparison result to the inverting input end of the first error amplifier, and the third end of the second reference load is connected with the ground.
Further, the first voltage-controlled current source comprises a transistor MP2 and a power supply VCC; the second voltage-controlled current source comprises a transistor MP1 and a power supply VCC; the first clamp circuit includes a transistor MP3; the first voltage division circuit comprises a resistor R7 and a resistor R8; the third error amplifier includes an amplifier AMP3;
the source electrode of the transistor MP1 is connected with a power supply VCC, the grid electrode of the transistor MP1 is connected with the grid electrode of the transistor MP2 and the output end of the amplifier AMP1, and the drain electrode of the transistor MP1 is connected with the port Iout and the anode of the resistor R1; the source electrode of the transistor MP2 is connected with a power supply VCC, the grid electrode of the transistor MP2 is connected with the grid electrode of the transistor MP1, and the drain electrode of the transistor MP2 is connected with the anode of the resistor R7 and the source electrode of the transistor MP3; the gate of the transistor MP3 is connected to the output terminal of the amplifier AMP3; the negative electrode of the resistor R7 is connected with the positive electrode of the resistor R8 and the inverting input end of the amplifier AMP3; the negative pole of the resistor R8 is connected to ground.
Further, the second voltage division circuit comprises a resistor R1 and a resistor R2; the first error amplifier includes an amplifier AMP1; the second error amplifier includes an amplifier AMP2; the first reference load comprises a resistor R5 and a resistor R9; the second reference load comprises a resistor R6 and a capacitor C3;
the positive pole of the resistor R9 is connected with the drain of the transistor MP3 and the positive pole of the resistor R5, the negative pole of the resistor R9 is connected with the ground, the positive pole of the resistor R1 is connected with the drain of the transistor MP1 and the output end Iout, the negative pole of the resistor R1 is connected with the positive pole of the resistor R2 and the non-inverting input end of the amplifier AMP3, the negative pole of the resistor R2 is connected with the ground, the positive pole of the resistor R6 is connected with the reference current port Iref and the positive pole of the capacitor C3 and the non-inverting input end of the amplifier AMP2, the negative pole of the resistor R6 is connected with the ground, the negative pole of the capacitor C3 is connected with the ground, the positive pole of the resistor R5 is connected with the positive pole of the resistor R9 and the drain of the transistor MP3, the negative pole of the resistor R5 is connected with the positive pole of the capacitor C2 and the inverting input end of the amplifier AMP2, the negative pole of the capacitor C2 is connected with the positive pole of the resistor R4, the negative pole of the output end of the amplifier AMP2, the amplifier 1 is connected with the negative pole of the amplifier AMP1, the negative pole of the current source AMP1 and the output end of the transistor MP1, the negative pole of the amplifier MP1 is connected with the ground, the gate of the power source.
Furthermore, the current of the current output end of the first voltage-controlled current source is controlled by the voltage of the voltage input end and the current output end of the first voltage-controlled current source, the current of the current output end of the second voltage-controlled current source is controlled by the voltage of the voltage input end and the current output end of the second voltage-controlled current source, the voltage of the first end of the first clamping circuit is controlled by the voltage of the second end of the first clamping circuit, the current of the third end of the first clamping circuit is the same as the current of the first end of the first clamping circuit, the ratio of the voltage of the first end of the first voltage-dividing circuit to the voltage of the second end of the first voltage-dividing circuit is equal to the ratio of the voltage of the first end of the second voltage-dividing circuit to the voltage of the fourth end of the second voltage-dividing circuit, the first voltage-dividing circuit samples the current output end voltage of the first voltage-controlled current source through the first end of the first voltage-dividing circuit, and the sampling result is input to the inverting input end of the third error amplifier through the second end of the first voltage-dividing circuit, the second voltage division circuit samples the voltage of the current output end of the second voltage-controlled current source through the first end of the second voltage division circuit, the sampling result is input to the non-inverting input end of the third error amplifier through the fourth end of the second voltage division circuit, the third error amplifier outputs a corresponding signal to the second end of the first clamping circuit according to the voltage of the non-inverting input end and the inverting input end of the third error amplifier, the second end of the first clamping circuit adjusts the voltage of the first end of the first clamping circuit until the voltage of the current output end of the first voltage-controlled current source is equal to the voltage of the current output end of the second voltage-controlled current source, so that the voltage of the non-inverting input end of the third error amplifier is the same as that of the inverting input end, at the moment, the voltage of the current output end of the first voltage-controlled current source is equal to the voltage of the current output end of the second voltage-controlled current source, and the voltage of the voltage input end of the first voltage-controlled current source is equal to the voltage of the voltage input end of the second voltage-controlled current source.
Further, the comparing the received signal frequency of the laser driver with the closed-loop bandwidth of the laser current bias circuit to control the output terminal Iout to output a high impedance or a low impedance includes:
when the signal frequency of a laser driver received by an output end Iout is lower than the closed-loop bandwidth of a laser current bias circuit, the current of a first end of a first voltage division circuit is smaller than the current of a first end of a first clamping circuit, the current of a second end of the first clamping circuit is smaller than the current of the first end of the first clamping circuit, the current of the first end of the first clamping circuit is the same as the current of a third end of the first clamping circuit, a first reference load samples the current of a current output end of a first voltage-controlled current source through the first end of the first reference load and converts the current into voltage, the voltage is output to a non-inverting input end of a second error amplifier through the second end of the first reference load, the non-inverting input end and the inverting input end of the second error amplifier are connected, when the ratio of the output current of the Iout to the input current of the reference current interface Iref is not equal to the preset ratio, the non-inverting input end and the inverting input end of the second error amplifier are connected, the non-inverting input end of the second error amplifier outputs the voltage difference between the voltage difference of the voltage-controlled current output end of the first voltage-controlled current source and the second voltage-controlled current output end of the second clamping circuit, and the voltage-controlled current source are changed through the voltage-controlled current output end of the second clamping circuit;
when the signal frequency of the laser driver received by the output end is higher than the closed loop bandwidth of the laser current bias circuit, the output end of the second error amplifier is equivalent to a reference voltage, the second voltage division circuit samples the voltage of the output end Iout through the first end of the second voltage division circuit and outputs the voltage to the non-inverting input end of the first error amplifier through the second end of the second voltage division circuit, the first error amplifier compares the voltages of the non-inverting input end and the inverting input end of the first error amplifier, the output end of the first error amplifier is connected with the voltage input end of the second voltage-controlled current source, the output current of the current output end of the second voltage-controlled current source is adjusted to enable the voltages of the non-inverting input end and the inverting input end of the first error amplifier to be the same, and the output end Iout outputs low impedance.
Further, the ratio of the positive electrode voltage to the negative electrode voltage of the resistor R7 is equal to the ratio of the positive electrode voltage to the negative electrode voltage of the resistor R1, the amplifier AMP3 compares the negative electrode voltage of the resistor R7 with the negative electrode voltage of the resistor R1, outputs the result to the gate of the transistor MP3, the gate voltage of the transistor MP3 controls the source voltage of the transistor MP3, and finally the voltage of the non-inverting input terminal of the amplifier AMP3 is the same as that of the inverting input terminal, so that the drain voltage of the transistor MP1 is the same as that of the transistor MP 2.
A control method of VCSEL laser current bias circuit,
controlling the closed-loop bandwidth of the laser current bias circuit to be lower than the low-frequency cut-off frequency of the laser driver, and obtaining a signal from the laser driver at the output end;
comparing the signal frequency of the laser driver with the closed loop bandwidth of the laser current bias circuit;
when the frequency of the signal from the laser driver at the output terminal is lower than the closed loop bandwidth of the laser current bias circuit, the voltage of the inverting input terminal of the amplifier AMP2 is higher than that of the non-inverting input terminal, the voltage of the output terminal of the amplifier AMP2 becomes lower, the voltage of the output terminal of the amplifier AMP1 becomes higher, the drain current of the transistor MP2 decreases, the voltage of the positive electrode of the resistor R9 decreases, the voltage of the inverting input terminal of the amplifier AMP2 decreases, the current flowing through the positive electrode of the resistor R7 is designed to be smaller than the current flowing through the drain of the transistor MP2, the current flowing through the positive electrode of the resistor R1 is designed to be smaller than the current flowing through the drain of the transistor MP1, and the ratio of the current flowing through the positive electrode of the resistor R9 to the current of the output terminal Iout is I R9 :Iout≈I MP2 :I MP1 S, the voltages of the non-inverting input end and the inverting input end of the amplifier AMP2 are the same, and the ratio of the current flowing through the positive electrode of the resistor R9 to the current flowing through the positive electrode of the resistor R6 is I R9 Iref = R6: R9= T: U, T and U are both positive real numbers, the current ratio of the current of the reference current interface Iref to the current of the output end Iout is Iref: iout = V: W, iout = Iref V/W is obtained, V and W are both positive real numbers, the bias current provided by the laser current bias circuit to the outside is adjusted by adjusting the input current of the reference current interface Iref, and the output end Iout outputs high impedance;
when the frequency of a signal from a laser driver on the output end is not lower than the closed-loop bandwidth of the laser current bias circuit, the voltage of the output end of the amplifier AMP1 is increased, the drain voltage of a transistor MP1 is reduced, the voltage of the anode of a resistor R2 is reduced, the voltage of the output end of the amplifier AMP1 is reduced, and the output end Iout outputs low impedance.
The invention achieves the following beneficial effects:
the laser current bias circuit provided by the invention provides high-precision and wide-range bias current for a laser, the output impedance of the laser current bias circuit is changed into low impedance through the voltage source generating unit, the laser current bias circuit is a current source circuit when the frequency of a signal from a laser driver on an output end is lower than the closed-loop bandwidth of the laser current bias circuit, and the laser current bias circuit is a voltage source circuit when the frequency of the signal from the laser driver on the output end is higher than the closed-loop bandwidth of the bias circuit. When the laser current bias circuit provided by the invention is used as a power supply of a laser driver chip, accurate current can be provided for a laser, the influence of the impedance of the laser bias circuit on the bandwidth and the gain of the laser driver can be avoided, meanwhile, when external factors change, the conduction voltage drop of the laser also changes, and the current of the current output end of the second voltage-controlled current source can be ensured to be unchanged under the action of negative feedback by the laser current bias circuit, so that the laser current bias circuit provided by the invention has the capability of self-adapting to the change of the conduction voltage drop of the laser.
Drawings
Fig. 1 is a block diagram of a VCSEL laser current bias circuit according to the present invention;
FIG. 2 is a schematic diagram of an embodiment of a VCSEL laser current bias circuit according to the present invention;
fig. 3 is a diagram of an embodiment of a laser driver to which the VCSEL laser current bias circuit of the present invention is applied.
Reference numerals:
1. a clamping unit; 2. a voltage source generating unit; 3. the load unit is referenced.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
As shown in fig. 1, a VCSEL laser current bias circuit, in particular to a VCSEL laser current bias circuit applied to anode modulation, includes a reference load unit 3, a clamping unit 1, a first voltage-controlled current source and a voltage source generating unit 2; the clamping unit 1 comprises a first clamping circuit, a first voltage division circuit and a third error amplifier, and the voltage source generating unit 2 comprises an output end Iout, a second voltage-controlled current source, a first error amplifier and a second voltage division circuit; the reference load unit 3 comprises a reference current interface Iref, a first reference load, a second reference load and a second error amplifier.
The first voltage-controlled current source is provided with a first end and a second end, the first end of the first voltage-controlled current source is a voltage input end, the second end of the first voltage-controlled current source is a current output end, the second voltage-controlled current source is provided with a first end and a second end, the first end of the second voltage-controlled current source is a voltage input end, the second end of the second voltage-controlled current source is a current output end, the voltage input end of the first voltage-controlled current source is connected with the voltage input end of the second voltage-controlled current source, and the current output end of the second voltage-controlled current source is connected with an output end Iout;
the first voltage-controlled current source and the second voltage-controlled current source are in a current mirror relationship, the current output end of the first voltage-controlled current source and the current output end of the second voltage-controlled current source are mainly controlled by the voltage of the voltage input end of the first voltage-controlled current source and are also influenced by the voltage of the current output end of the second voltage-controlled current source, so that the first voltage-controlled current source and the second voltage-controlled current source have a high-precision current mirror relationship, the clamping unit 1 is used for enabling the voltage of the current output end of the first voltage-controlled current source to be equal to the voltage of the current output end of the second voltage-controlled current source;
the invention provides a VCSEL laser current bias circuit, which aims to provide high-precision direct current bias current outwards through an output end Iout without influencing the high-frequency performance of a laser driver, wherein the output end Iout is connected with the laser driver and then provided with a signal from the laser driver, the closed-loop bandwidth of the laser current bias circuit is designed to be lower than the low-frequency cut-off frequency of the laser driver, when the frequency of the signal from the laser driver on the output end is lower than the closed-loop bandwidth of the laser current bias circuit, the laser current bias circuit is used as a current source generating unit, and the output end Iout provides the high-precision bias current for the VCSEL laser;
when the frequency of the signal from the laser driver on the output end is higher than the closed-loop bandwidth of the laser current bias circuit, the current source generating unit fails, the voltage source generating unit 2 has the function that when the current source generating unit fails, the voltage source generating unit 2 enables the output end Iout to externally provide constant voltage, namely when the frequency of the signal from the laser driver on the output end is lower than the closed-loop bandwidth of the laser current bias circuit, the output end Iout is a current source and outputs high impedance, and when the frequency of the signal from the laser driver on the output end is higher than the closed-loop bandwidth of the laser current bias circuit, the output end Iout is a voltage source and outputs low impedance;
the clamping unit 1 comprises a first clamping circuit, a first voltage division circuit and a third error amplifier; the first end of the first clamping circuit is connected with the current output end of the first voltage-controlled current source, the second end of the first clamping circuit is connected with the output end of the third error amplifier, the first end of the first voltage-dividing circuit is connected with the current output end of the first voltage-controlled current source and the first end of the first clamping circuit, the second end of the first voltage-dividing circuit is connected with the inverting input end of the third error amplifier, and the third end of the first voltage-dividing circuit is connected with the ground.
The current source generating unit comprises a first clamping circuit, a first voltage division circuit and a third error amplifier in the clamping unit 1, and further comprises a second voltage division circuit, a first error amplifier, a second error amplifier, a first reference load, a second reference load, a first voltage-controlled current source and a second voltage-controlled current source; the non-inverting input end of the third error amplifier is connected with the fourth end of the second voltage-controlled current source, the first end of the second voltage-controlled current source is connected with the current output end and the output end Iout of the second voltage-controlled current source, the second end of the second voltage-controlled circuit is connected with the non-inverting input end of the first error amplifier, the inverting input end of the first error amplifier is connected with the output end of the second error amplifier, the output end of the first error amplifier is connected with the voltage input end of the first voltage-controlled current source and the voltage input end of the second voltage-controlled current source, the first end of the first reference load is connected with the third end of the first clamping circuit, the second end of the first reference load is connected with the inverting input end of the second error amplifier, the third end of the first reference load is connected with the ground, the non-inverting input end of the second error amplifier is connected with the second end of the second reference load, the first end of the second reference load is connected with the reference current interface Iref, and the third end of the second reference load is connected with the ground.
The voltage source generating unit 2 includes a second voltage-controlled current source, a first error amplifier, and a second voltage dividing circuit in the current source generating unit.
The corresponding control method comprises the following steps: the current of the second end of the first voltage-controlled current source is controlled by the voltage of the voltage input end of the first voltage-controlled current source and the voltage of the second end, the current of the second end of the second voltage-controlled current source is controlled by the voltage of the voltage input end of the second voltage-controlled current source and the voltage of the second end, the voltage of the first end of the first clamping circuit is controlled by the voltage of the second end of the first clamping circuit, the current of the third end of the first clamping circuit is the same as the current of the first end of the first clamping circuit, the ratio of the voltage of the first end of the first voltage division circuit to the voltage of the second end of the first voltage division circuit is equal to the ratio of the voltage of the first end of the second voltage division circuit to the voltage of the fourth end of the second voltage division circuit, the first voltage division circuit samples the voltage of the second end of the first voltage-controlled current source through the first voltage division circuit, and the sampling result is input to the inverting input end of the third error amplifier through the second end of the first voltage division circuit, the second voltage division circuit samples the current output end voltage of the second voltage-controlled current source through the first end of the second voltage division circuit, the sampling result is input to the non-inverting input end of the third error amplifier through the fourth end of the second voltage division circuit, the third error amplifier outputs corresponding signals to the second end of the first clamping circuit according to the voltages of the non-inverting input end and the inverting input end, the second end of the first clamping circuit adjusts the voltage of the first end of the first clamping circuit until the current output end voltage of the first voltage-controlled current source is equal to the current output end voltage of the second voltage-controlled current source, therefore, the voltages of the non-inverting input end and the inverting input end of the third error amplifier are the same, the clamping unit 1 works stably, at the moment, the current output end voltage of the first voltage-controlled current source is equal to the current output end voltage of the second voltage-controlled current source, the voltage input end voltage of the first voltage-controlled current source is equal to the voltage input end voltage of the second voltage-controlled current source, therefore, the current of the second end of the first voltage-controlled current source and the current of the second end of the second voltage-controlled current source have an accurate proportional relation;
when the ratio of the output current of the output terminal Iout and the input current of the reference current interface Iref is not equal to the designed ratio of the circuit, the in-phase input terminal of the second reference load and the second terminal of the second reference load are output to the in-phase input terminal of the second error amplifier, and the comparison result between the in-phase input terminal of the second reference current amplifier and the second voltage output terminal of the second error amplifier is lower than the comparison result of the first voltage control error amplifier and the second voltage control error amplifier, when the ratio of the output current of the output terminal Iout and the input current of the reference current interface Iref is not equal to the ratio of the input current of the voltage control error amplifier, the first voltage control error amplifier generates an accurate ratio result, and when the first voltage control error amplifier generates an accurate ratio result, the first voltage control error amplifier outputs a frequency error signal, and the second voltage control error amplifier outputs a frequency signal, and the second voltage control error amplifier outputs a voltage signal, and the first voltage control error amplifier outputs a frequency control signal, and the second error amplifier output frequency control signal, and the output error amplifier output frequency control signal are equal to the output frequency control signal, the output impedance is high impedance; when the frequency of a signal from the laser driver on the output end is higher than the bandwidth of the current source generation unit, the output end of the second error amplifier is equivalent to a reference voltage, the second voltage division circuit samples the voltage of the output end Iout through the first end of the second voltage division circuit and outputs the voltage to the non-inverting input end of the first error amplifier through the second end of the second voltage division circuit, the first error amplifier compares the voltages of the non-inverting input end and the inverting input end, the output end of the first error amplifier is connected to the voltage input end of the second voltage-controlled current source, the output current of the second end of the second voltage-controlled current source is adjusted to ensure that the voltages of the non-inverting input end and the inverting input end of the first error amplifier are the same, the voltage of the second end of the second voltage division circuit and the voltage of the first end have an accurate proportional relation, so that when the frequency of the signal from the laser driver on the output end is higher than the bandwidth of the current source generation unit, the output end Iout becomes a voltage source, and the output impedance is equal to the reference voltage.
Fig. 2 is an embodiment of a VCSEL laser current bias circuit according to the present invention, and the specific implementation is as follows:
the first voltage-controlled current source comprises a transistor MP2 and a power supply VCC; the second voltage-controlled current source comprises a transistor MP1 and a power supply VCC; the first clamp circuit includes a transistor MP3; the first voltage division circuit comprises a resistor R7 and a resistor R8; the third error amplifier includes an amplifier AMP3;
the source electrode of the transistor MP1 is connected with a power supply VCC, the grid electrode of the transistor MP1 is connected with the grid electrode of the transistor MP2 and the output end of the amplifier AMP1, and the drain electrode of the transistor MP1 is connected with the output end Iout and the anode of the resistor R1; the source electrode of the transistor MP2 is connected with a power supply VCC, the grid electrode of the transistor MP2 is connected with the grid electrode of the transistor MP1, and the drain electrode of the transistor MP2 is connected with the anode of the resistor R7 and the source electrode of the transistor MP3; the gate of the transistor MP3 is connected to the output terminal of the amplifier AMP3; the negative electrode of the resistor R7 is connected with the positive electrode of the resistor R8 and the inverting input end of the amplifier AMP3; the negative pole of the resistor R8 is connected to ground.
The second voltage division circuit comprises a resistor R1 and a resistor R2; the first error amplifier includes an amplifier AMP1; the second error amplifier includes an amplifier AMP2; the first reference load comprises a resistor R5 and a resistor R9; the second reference load comprises a resistor R6 and a capacitor C3;
the positive pole of the resistor R9 is connected with the drain of the transistor MP3 and the positive pole of the resistor R5, the negative pole of the resistor R9 is connected with the ground, the positive pole of the resistor R1 is connected with the drain of the transistor MP1 and the output end Iout, the negative pole of the resistor R1 is connected with the positive pole of the resistor R2 and the non-inverting input end of the amplifier AMP3, the negative pole of the resistor R2 is connected with the ground, the positive pole of the resistor R6 is connected with the reference current port Iref and the positive pole of the capacitor C3 and the non-inverting input end of the amplifier AMP2, the negative pole of the resistor R6 is connected with the ground, the negative pole of the capacitor C3 is connected with the ground, the positive pole of the resistor R5 is connected with the positive pole of the resistor R9 and the drain of the transistor MP3, the negative pole of the resistor R5 is connected with the positive pole of the capacitor C2 and the inverting input end of the amplifier AMP2, the negative pole of the capacitor C2 is connected with the positive pole of the resistor R4, the negative pole of the output end of the amplifier AMP2, the amplifier 1 is connected with the negative pole of the amplifier AMP1, the negative pole of the current source AMP1 and the output end of the transistor MP1, the negative pole of the amplifier MP1 is connected with the ground, the gate of the power source.
As shown in FIG. 2, the transistor MP3, the resistor R7, the resistor R8 and the amplifier AMP3 constitute a clamp unit 1, and the ratio of the width-to-length ratio of the transistor MP2 to the width-to-length ratio of the transistor MP1 is first designed to be (W/L) MP2 :(W/L) MP1 S, R and S are both positive real numbers, and the clamping unit 1 makes the drain voltage of the transistor MP2 the same as the drain voltage of the transistor MP1, so the ratio of the drain current of the transistor MP2 to the drain current of the transistor MP1 is I MP2 :I MP1 (ii) = R: S; the method comprises the following specific steps: the ratio of the positive electrode voltage and the negative electrode voltage of the resistor R7 is equal to the ratio of the positive electrode voltage and the negative electrode voltage of the resistor R1, the amplifier AMP3 compares the negative electrode voltage of the resistor R7 with the negative electrode voltage of the resistor R1, the result is output to the grid electrode of the transistor MP3, the grid electrode voltage of the transistor MP3 controls the source electrode voltage of the transistor MP3, finally the voltage of the non-inverting input end of the amplifier AMP3 is the same as that of the inverting input end, namely the drain electrode voltage of the transistor MP1 is the same as that of the transistor MP2, and therefore the drain electrode current of the transistor MP1 and the drain electrode current of the transistor MP2 have an accurate proportional relation.
As shown in FIG. 2, the laser current bias circuit as a whole constitutes a current source generating unit, and first, when the voltage at the inverting input terminal of the amplifier AMP2 is higher than the voltage at the non-inverting input terminal, the voltage at the output terminal of the amplifier AMP2 becomes low, the output terminal of the amplifier AMP2 is connected to the inverting input terminal of the amplifier AMP1, and therefore the voltage at the output terminal of the amplifier AMP1 risesWhen the current is high, the drain current of the transistor MP2 is reduced, the voltage of the positive electrode of the resistor R9 is reduced, and the voltage of the inverting input end of the amplifier AMP2 is reduced, so that the whole circuit is a negative feedback loop; secondly, the current flowing through the anode of the resistor R7 is far smaller than the current flowing through the drain of the transistor MP2, and the current flowing through the anode of the resistor R1 is far smaller than the current flowing through the drain of the transistor MP1, so that the current ratio of the current flowing through the anode of the resistor R9 to the current of the output end Iout is I R9 :Iout≈I MP2 :I MP1 S, the voltage of the non-inverting input end and the inverting input end of the amplifier AMP2 is the same because the whole circuit is closed loop negative feedback and the virtual short effect of the amplifier, so that the current I flowing through the positive electrode of the resistor R9 R9 The ratio of the current Iref flowing through the positive electrode of the resistor R6 is I R9 Iref = R6: R9= T: U, and T and U are both positive real numbers, so that the current ratio of the input current of the reference current interface Iref to the current of the output end Iout is Iref: iout = V: W, i.e. Iout = Iref V/W, and both V and W are both positive real numbers, and therefore, the bias current provided by the laser current bias circuit to the outside can be adjusted by adjusting the input current of the reference current interface Iref;
as shown in fig. 2, the transistor MP1, the resistor R2, the amplifier AMP1, the current source I1, the resistor R3, and the capacitor C1 form a voltage source generating unit 2, the closed-loop bandwidth of the current source generating unit is designed to be lower than the low-frequency cutoff frequency of the laser driver, when the frequency is higher than the bandwidth of the current source generating unit, the current source generating unit fails, and if the voltage at the output terminal of the amplifier AMP1 increases, the drain voltage of the MP1 transistor decreases, the positive voltage of the resistor R2 decreases, and the non-inverting input terminal of the amplifier AMP1 is connected to the positive terminal of the resistor R2, so that the voltage at the output terminal of the amplifier AMP1 decreases, and in sum, when the frequency of the signal from the laser driver at the output terminal is higher than the closed-loop bandwidth of the current source generating unit, the output terminal Iout outputs a low impedance.
Fig. 3 is an example of a VCSEL laser driver applying the VCSEL laser current bias circuit provided in the present invention, and the specific implementation is as follows:
the grid electrode of the transistor M1 is connected with a Vinn port, the source electrode of the transistor M1 is connected with the anode of the current source I1, and the drain electrode of the transistor M1 is connected with the cathode of the resistor R10 and the anode of the VCSEL laser V1;
the grid electrode of the transistor M2 is connected with the Vinp, the source electrode of the transistor M2 is connected with the anode of the current source I1, and the drain electrode of the transistor M2 is connected with the cathode of the resistor R20;
the anode of the current source I1 is connected with the source electrode of the transistor M1 and the source electrode of the transistor M2, and the cathode of the current source I1 is connected with the ground;
the anode of the resistor R10 is connected with the output end Iout of the current bias circuit provided by the invention, and the cathode of the resistor R1 is connected with the anode of the VCSEL laser and the drain of the transistor M1;
the anode of the resistor R20 is connected with a power supply VCC, and the cathode of the resistor R20 is connected with the drain of the transistor M2;
the output end Iout of the current bias circuit provided by the invention is connected with the anode of the resistor R1;
the anode of the VCSEL laser is connected with the cathode of the resistor R10 and the drain of the transistor M1, and the cathode of the VCSEL laser is connected with the ground;
as shown in fig. 3, the bias current of the VCSEL laser is equal to the output current of the output terminal Iout minus the bias current of the transistor M1, and the bias current of the transistor M1 is provided by the tail current source I1, so that the VCSEL laser V1 can be provided with a high-precision and wide-range bias current by changing the output current of the output terminal Iout; meanwhile, the output current of the output end Iout provided by the laser current bias circuit provided by the invention is only related to the Iref shown in fig. 2 and is unrelated to the bias voltage of the VCSEL laser, so that under the same VCSEL laser bias current, when the bias voltage of the VCSEL laser changes along with the change of the external environment, the laser current bias circuit provided by the invention can adapt to the bias voltage change of the laser and still provide high-precision output current; meanwhile, the bandwidth of a current source generating unit of the laser current biasing circuit provided by the invention is designed to be lower than the low-frequency cut-off frequency of a laser driver, so that the output impedance of the laser current biasing circuit provided by the invention is always low in a target frequency range, and the bandwidth and the low-frequency cut-off frequency of the laser driver are not influenced by the VCSEL current biasing circuit provided by the invention.
In summary, the laser current bias circuit provided by the invention provides a high-precision and wide-range bias current for the laser through the current source generating unit, and the output impedance of the laser current bias circuit is changed into low impedance through the voltage source generating unit 2. Therefore, the laser current bias circuit provided by the invention is a current source circuit when the frequency is lower than the closed-loop bandwidth of the current source generation unit, and is a voltage source circuit when the frequency is higher than the closed-loop bandwidth of the current source generation unit. Therefore, the laser current bias circuit provided by the invention becomes a voltage source capable of providing high-precision and wide-range current. Therefore, when the laser current bias circuit provided by the invention is used as a power supply of a laser driver chip, accurate current can be provided for a laser, the influence of the impedance of the laser bias circuit on the bandwidth and the gain of the laser driver can be avoided, meanwhile, when external factors change, the conduction voltage drop of the laser also changes, and the current of the current output end of the second voltage-controlled current source can be ensured to be unchanged under the action of negative feedback by the current source generating unit, so that the laser current bias circuit provided by the invention has the capability of self-adapting to the change of the conduction voltage drop of the laser.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, it is possible to make various improvements and modifications without departing from the technical principle of the present invention, and those improvements and modifications should be considered as the protection scope of the present invention.
Claims (10)
1. A VCSEL laser current bias circuit, comprising: the voltage-controlled power supply comprises a first voltage-controlled current source, a clamping unit, a reference load unit and a voltage source generating unit; the reference load unit is provided with a reference current interface Iref; the voltage source generating unit is provided with a second voltage-controlled current source and an output end Iout;
the first voltage-controlled current source and the second voltage-controlled current source are respectively provided with a voltage input end and a current output end, the voltage input end of the first voltage-controlled current source is connected with the voltage input end of the second voltage-controlled current source, and the current output end of the second voltage-controlled current source is connected with the output end Iout; the output end Iout is used for outputting bias current for the laser;
the clamping unit is connected with the first voltage-controlled current source and the voltage source generating unit and is used for enabling the current output end voltage of the first voltage-controlled current source to be equal to the current output end voltage of the second voltage-controlled current source;
the reference load unit is respectively connected with the clamping unit and the voltage source generating unit;
the output end Iout is connected with the laser driver, receives a signal of the laser driver, and is used for comparing the frequency of the received signal of the laser driver with the closed-loop bandwidth of the laser current bias circuit and controlling the output end Iout to output high impedance or low impedance.
2. The VCSEL laser current bias circuit of claim 1, wherein the clamping unit comprises a first clamping circuit, a first voltage divider circuit, and a third error amplifier;
the first end of the first voltage division circuit is used for sampling the voltage of the current output end of the first voltage-controlled current source, the second end of the first voltage division circuit is used for transmitting the voltage signal of the current output end of the first voltage-controlled current source sampled by the first end to the inverting input end of the third error amplifier, and the third end of the first voltage division circuit is connected with the ground;
the first end of the first clamping circuit is connected with the current output end of the first voltage-controlled current source, the second end of the first clamping circuit is connected with the output end of the third error amplifier, and the third error amplifier is used for controlling the voltage of the first end of the first clamping circuit through the second end of the first clamping circuit so as to control the voltage of the current output end of the first voltage-controlled current source;
the third end of the first clamping circuit is connected with a reference load unit, and the reference load unit samples the current of the first end of the first clamping circuit through the third end of the first clamping circuit, so that the current of the current output end of the first voltage-controlled current source is sampled.
3. The VCSEL laser current bias circuit of claim 2, wherein the voltage source generating unit further comprises a second voltage dividing circuit and a first error amplifier;
the first end of the second voltage division circuit is used for sampling the voltage of the current output end of the second voltage-controlled current source and inputting the sampling result into the non-inverting input end of the third error amplifier through the fourth end of the second voltage division circuit, and the first end of the second voltage division circuit is also used for sampling the voltage of the output end Iout and outputting the voltage to the non-inverting input end of the first error amplifier through the second end of the second voltage division circuit;
the inverting input end of the first error amplifier is connected with the reference load unit, the first error amplifier is used for comparing the voltages of the non-inverting input end and the inverting input end, and the output end of the first error amplifier is connected with the voltage input end of the second voltage-controlled current source and used for adjusting the output current of the current output end of the second voltage-controlled current source to enable the voltages of the non-inverting input end and the inverting input end of the first error amplifier to be the same; the third terminal of the second voltage division circuit is connected to ground.
4. The VCSEL laser current bias circuit of claim 3, wherein the reference load unit further comprises a second error amplifier, a first reference load, and a second reference load;
the first end of the first reference load is connected with the third end of the first clamping circuit and used for sampling the current of the current output end of the first voltage-controlled current source and converting the current into voltage which is output to the inverting input end of the second error amplifier through the second end of the first reference load;
the reference current interface Iref input current is sampled through the first end of the second reference load and converted into voltage, the voltage is output to the non-inverting input end of the second error amplifier through the second end of the second reference load, the second error amplifier is used for comparing the voltages of the non-inverting input end and the inverting input end of the second error amplifier and outputting the comparison result to the inverting input end of the first error amplifier, and the third end of the second reference load is connected with the ground.
5. A VCSEL laser current bias circuit according to claim 3, wherein the first voltage controlled current source comprises transistor MP2 and power supply VCC; the second voltage-controlled current source comprises a transistor MP1 and a power supply VCC; the first clamp circuit includes a transistor MP3; the first voltage division circuit comprises a resistor R7 and a resistor R8; the third error amplifier includes an amplifier AMP3;
the source electrode of the transistor MP1 is connected with a power supply VCC, the grid electrode of the transistor MP1 is connected with the grid electrode of the transistor MP2 and the output end of the amplifier AMP1, and the drain electrode of the transistor MP1 is connected with the port Iout and the anode of the resistor R1; the source electrode of the transistor MP2 is connected with a power supply VCC, the grid electrode of the transistor MP2 is connected with the grid electrode of the transistor MP1, and the drain electrode of the transistor MP2 is connected with the anode of the resistor R7 and the source electrode of the transistor MP3; the gate of the transistor MP3 is connected to the output terminal of the amplifier AMP3; the negative electrode of the resistor R7 is connected with the positive electrode of the resistor R8 and the inverting input end of the amplifier AMP3; the negative pole of the resistor R8 is connected to ground.
6. A VCSEL laser current bias circuit according to claim 5, wherein the second divider circuit includes a resistor R1 and a resistor R2; the first error amplifier includes an amplifier AMP1; the second error amplifier includes an amplifier AMP2; the first reference load comprises a resistor R5 and a resistor R9; the second reference load comprises a resistor R6 and a capacitor C3;
the positive pole of the resistor R9 is connected with the drain of the transistor MP3 and the positive pole of the resistor R5, the negative pole of the resistor R9 is connected with the ground, the positive pole of the resistor R1 is connected with the drain of the transistor MP1 and the output end Iout, the negative pole of the resistor R1 is connected with the positive pole of the resistor R2 and the non-inverting input end of the amplifier AMP3, the negative pole of the resistor R2 is connected with the ground, the positive pole of the resistor R6 is connected with the reference current port Iref and the positive pole of the capacitor C3 and the non-inverting input end of the amplifier AMP2, the negative pole of the resistor R6 is connected with the ground, the negative pole of the capacitor C3 is connected with the ground, the positive pole of the resistor R5 is connected with the positive pole of the resistor R9 and the drain of the transistor MP3, the negative pole of the resistor R5 is connected with the positive pole of the capacitor C2 and the inverting input end of the amplifier AMP2, the negative pole of the capacitor C2 is connected with the positive pole of the resistor R4, the negative pole of the output end of the amplifier AMP2, the amplifier 1 is connected with the negative pole of the amplifier AMP1, the negative pole of the current source AMP1 and the output end of the transistor MP1, the negative pole of the amplifier MP1 is connected with the ground, the gate of the power source.
7. The VCSEL laser current bias circuit of claim 3, wherein a current output terminal of the first voltage controlled current source is controlled by a voltage of a voltage input terminal and a current output terminal of the first voltage controlled current source, a current of a current output terminal of the second voltage controlled current source is controlled by a voltage of a voltage input terminal and a current output terminal of the second voltage controlled current source, a first terminal voltage of the first clamp circuit is controlled by a second terminal voltage of the first clamp circuit, a third terminal current of the first clamp circuit is the same as the first terminal current of the first clamp circuit, a ratio of the first terminal voltage of the first voltage divider circuit to the second terminal voltage of the first voltage divider circuit is equal to a ratio of the first terminal voltage of the second voltage divider circuit to the fourth terminal voltage of the second voltage divider circuit, the first voltage divider circuit samples a current output terminal voltage of the first voltage controlled current source through the first terminal of the first voltage divider circuit, the sampling result is input to the inverting input end of a third error amplifier through the second end of a first voltage division circuit, the second voltage division circuit samples the voltage of the current output end of a second voltage-controlled current source through the first end of a second voltage division circuit, the sampling result is input to the non-inverting input end of a third error amplifier through the fourth end of the second voltage division circuit, the third error amplifier outputs a corresponding signal to the second end of a first clamping circuit according to the voltage of the non-inverting input end and the inverting input end of the third error amplifier, the second end of the first clamping circuit adjusts the voltage of the first end of the first clamping circuit until the voltage of the current output end of the first voltage-controlled current source is equal to the voltage of the current output end of the second voltage-controlled current source, the voltage of the non-inverting input end and the inverting input end of the third error amplifier are the same, and the voltage of the voltage output end of the current of the first voltage-controlled current source is equal to the voltage of the current output end of the second voltage-controlled current source at the moment, the voltage at the voltage input of the first voltage controlled current source is equal to the voltage at the voltage input of the second voltage controlled current source.
8. A VCSEL laser current bias circuit according to claim 4, wherein the comparing the received signal frequency of the laser driver with the closed loop bandwidth of the laser current bias circuit to control the output terminal Iout to output a high impedance or a low impedance comprises:
when the signal frequency of a laser driver received by an output end Iout is lower than the closed-loop bandwidth of a laser current bias circuit, the current of a first end of a first voltage division circuit is smaller than the current of a first end of a first clamping circuit, the current of a second end of the first clamping circuit is smaller than the current of the first end of the first clamping circuit, the current of the first end of the first clamping circuit is the same as the current of a third end of the first clamping circuit, a first reference load samples the current of a current output end of a first voltage-controlled current source through the first end of the first reference load and converts the current into voltage, the voltage is output to a non-inverting input end of a second error amplifier through the second end of the first reference load, the non-inverting input end and the inverting input end of the second error amplifier are connected, when the ratio of the output current of the Iout to the input current of the reference current interface Iref is not equal to the preset ratio, the non-inverting input end and the inverting input end of the second error amplifier are connected, the non-inverting input end of the second error amplifier outputs the voltage difference between the voltage difference of the voltage-controlled current output end of the first voltage-controlled current source and the second voltage-controlled current output end of the second clamping circuit, and the voltage-controlled current source are changed through the voltage-controlled current output end of the second clamping circuit;
when the signal frequency of the laser driver received by the output end is higher than the closed-loop bandwidth of the laser current bias circuit, the output end of the second error amplifier is equivalent to a reference voltage, the second voltage division circuit samples the voltage of the output end Iout through the first end of the second voltage division circuit and outputs the voltage to the non-inverting input end of the first error amplifier through the second end of the second voltage division circuit, the first error amplifier compares the voltages of the non-inverting input end and the inverting input end of the first error amplifier, the output end of the first error amplifier is connected with the voltage input end of the second voltage-controlled current source, the output current of the current output end of the second voltage-controlled current source is adjusted to enable the voltages of the non-inverting input end and the inverting input end of the first error amplifier to be the same, and the output end Iout outputs low impedance.
9. The VCSEL laser current bias circuit of claim 5, wherein a ratio of a positive polarity voltage to a negative polarity voltage of the resistor R7 is equal to a ratio of a positive polarity voltage to a negative polarity voltage of the resistor R1, the amplifier AMP3 compares the negative polarity voltage of the resistor R7 with the negative polarity voltage of the resistor R1 and outputs a result to a gate of the transistor MP3, a gate voltage of the transistor MP3 controls a source voltage of the transistor MP3, and finally a voltage at a non-inverting input terminal of the amplifier AMP3 is the same as the voltage at a inverting input terminal so that a drain voltage of the transistor MP1 is the same as the drain voltage of the transistor MP 2.
10. A control method for the VCSEL laser current bias circuit according to claim 6,
controlling the closed-loop bandwidth of the laser current bias circuit to be lower than the low-frequency cut-off frequency of the laser driver, and obtaining a signal from the laser driver at the output end;
comparing the signal frequency of the laser driver with the closed loop bandwidth of the laser current bias circuit;
when the frequency of the signal from the laser driver at the output terminal is lower than the closed loop bandwidth of the laser current bias circuit, the voltage of the inverting input terminal of the amplifier AMP2 is higher than that of the non-inverting input terminal, the voltage of the output terminal of the amplifier AMP2 becomes lower, the voltage of the output terminal of the amplifier AMP1 becomes higher, the drain current of the transistor MP2 decreases, the voltage of the positive electrode of the resistor R9 decreases, the voltage of the inverting input terminal of the amplifier AMP2 decreases, the current flowing through the positive electrode of the resistor R7 is designed to be smaller than the current flowing through the drain of the transistor MP2, the current flowing through the positive electrode of the resistor R1 is designed to be smaller than the current flowing through the drain of the transistor MP1, and the ratio of the current flowing through the positive electrode of the resistor R9 to the current of the output terminal Iout is I R9 Iout = R: S, R and S are positive real numbers, the voltages of the non-inverting input end and the inverting input end of the amplifier AMP2 are the same, and the ratio of the current flowing through the positive electrode of the resistor R9 to the current flowing through the positive electrode of the resistor R6 is I R9 Iref = R6: R9= T: U, T and U are both positive real numbers, the ratio of the current of the reference current interface Iref to the current of the output end Iout is Iref: iout = V: W, iout = Iref V/W is obtained, V and W are both positive real numbers, and the bias externally provided by the laser current bias circuit is adjusted by adjusting the input current of the reference current interface IrefSetting the current, and outputting high impedance by an output end Iout;
when the frequency of a signal from a laser driver on the output end is not lower than the closed-loop bandwidth of the laser current bias circuit, the voltage of the output end of the amplifier AMP1 is increased, the drain voltage of a transistor MP1 is reduced, the voltage of the anode of a resistor R2 is reduced, the voltage of the output end of the amplifier AMP1 is reduced, and the output end Iout outputs low impedance.
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| US20080304527A1 (en) * | 2007-06-07 | 2008-12-11 | Miaobin Gao | Controlling a bias current for an optical source |
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