Linear laser driving circuit

Abstract

The invention provides a linear laser driving circuit, which comprises a primary linear amplifier, a linear branch and a nonlinear branch, and is characterized in that the nonlinear branch is used for receiving a differential voltage signal output by the primary linear amplifier and outputting a nonlinear compensation signal to compensate the nonlinear effect of a laser; and the output end of the nonlinear branch is connected with the output end of the linear branch, so that the compensation signal output by the nonlinear branch and the driving signal output by the linear branch are superposed to form an output electric signal. Therefore, the nonlinear effect of the laser can be compensated, the linearity of the optical signal output by the laser can be enhanced, and the performance of the optical eye diagram can be optimized.

Description

Technical Field

[0001] The invention relates to the technical field of circuits, and in particular to a linear laser driving circuit. Background Art

[0002] In linear optical communication systems, such as Figure 1 As shown, the input voltage signal is first processed by a linear laser driver 10, and the signal output by the laser driver 10 is a linearly amplified or reduced signal of the input voltage signal. After the input voltage signal passes through the laser driver 10, a voltage signal or a current signal is generated to drive the laser 20 to convert the voltage signal or the current signal into an optical signal, and transmit it through an optical coupler or an optical fiber. However, due to the nonlinear characteristics of the laser itself, the nonlinear characteristics will introduce distortion in the conversion process, which is specifically manifested as the skewness of the optical eye diagram of the optical signal output by the laser or the inconsistent eye height.

[0003] like Figure 2 and Figure 3 As shown, under the ideal linearity of the laser driver, the input voltage signal has four levels (called 0 / 1 / 2 / 3 levels), and multiple periodic signals are superimposed to form the following Figure 2 and Figure 3 The eye diagram shown in Figure 3 The arrows in the figure represent the height of each eye (when linearity is ideal, the height of the eyes is consistent) and the sampling position of the eyes (when linearity is ideal, the sampling position of the eyes is also consistent).

[0004] If the linearity of the laser driver 10 is good, the eye diagram of the output signal is also very linear, and the eye diagram of the output signal shows that the three eyes are not skewed and the heights of the three eyes are consistent. Figure 4 As shown, it is the optical eye diagram output by the laser (i.e. Figure 1 The optical eye diagram of the sampling point z in the optical signal transmission is obtained by measuring the optical eye diagram of the sampling point z in the optical signal transmission device. Due to the nonlinearity of the laser itself, the optical eye diagram of the final output will be skewed or have inconsistent eye heights. Since the final sampling can only be performed at a fixed eye diagram position, the skewed eye diagram and / or inconsistent eye height will cause the three eyes to be unable to sample at the optimal sampling point at the same time, thereby causing problems such as an increase in the communication bit error rate and a decrease in communication sensitivity. In the prior art, the linear performance of the laser driver is improved to ensure that it meets the requirements of linear amplification. However, even if the laser driver achieves the ideal linear amplification effect, the nonlinear characteristics of the laser itself will still limit the transmission performance of the entire system, that is, it is impossible to compensate for the distortion of the optical eye diagram caused by the nonlinearity of the laser, resulting in a skewed optical eye diagram, or the laser driver has a certain nonlinear compensation capability, but it cannot be adjusted freely and cannot adapt to different types of lasers and different operating temperatures. Summary of the invention

[0005] The object of the present invention is to provide a linear laser driving circuit to offset the nonlinear effect of the laser itself, enhance the linearity of the optical signal, and optimize the performance of the optical eye diagram.

[0006] To achieve the above object, the present invention provides a linear laser driving circuit, comprising:

[0007] A primary linear amplifier, used to amplify an input differential voltage signal and output the amplified differential voltage signal, wherein the differential voltage signal includes a positive voltage signal and a negative voltage signal;

[0008] A linear branch, used for receiving the differential voltage signal output by the primary linear amplifier and outputting a linear driving signal;

[0009] A nonlinear branch is used to receive the differential voltage signal output by the primary linear amplifier and output a nonlinear compensation signal to compensate for the nonlinear effect of the laser. The output end of the nonlinear branch is connected to the output end of the linear branch so that the compensation signal is superimposed on the drive signal to form an output electrical signal, and the output electrical signal is provided to the laser to convert the output electrical signal into an optical signal.

[0010] Optionally, the linear branch includes: a first transistor and an adjustable first resistor, the first electrode of the first transistor is connected to the first output end of the primary linear amplifier to input the forward voltage signal, the second electrode of the first transistor is connected to the power supply voltage or ground, the third electrode of the first transistor is connected to one end of the first resistor, the other end of the first resistor is the output end of the linear branch to output the drive signal, and the other end of the first resistor is connected to the output end of the nonlinear branch.

[0011] Optionally, the nonlinear branch includes: a second transistor and an adjustable second resistor, the first electrode of the second transistor is connected to the second output terminal of the primary linear amplifier to input the negative voltage signal, the second electrode of the second transistor is connected to the first resistor, and the third electrode of the second transistor is connected to the second resistor, wherein the second electrode of the second transistor is the output terminal of the nonlinear branch to output the compensation signal.

[0012] Optionally, the nonlinear branch includes: a second transistor, a third transistor and an adjustable second resistor, the first electrode of the second transistor is connected to the second output terminal of the primary linear amplifier to input the negative voltage signal, the first electrode of the third transistor is connected to the first bias voltage, the second electrode of the third transistor is connected to the first resistor, the third electrode of the third transistor is connected to the second electrode of the second transistor, and the third electrode of the second transistor is connected to the second resistor, wherein the second electrode of the third transistor is the output terminal of the nonlinear branch to output the compensation signal.

[0013] Optionally, the nonlinear branch also includes a fourth transistor, which is coupled between the power supply voltage and the third transistor, wherein a first electrode of the fourth transistor is connected to a second bias voltage, a second electrode of the fourth transistor is connected to the power supply voltage or ground, and a third electrode of the fourth transistor is connected to a third electrode of the third transistor and a second electrode of the second transistor.

[0014] Optionally, the nonlinear branch also includes a fifth transistor and a fifth current source, the fifth transistor being coupled between the first electrode of the second transistor and the second output terminal of the primary linear amplifier, the first electrode of the fifth transistor being connected to the second output terminal of the primary linear amplifier, the second electrode of the fifth transistor being connected to the power supply voltage or ground, the third electrode of the fifth transistor being connected to the first electrode of the second transistor, and the fifth current source being coupled between the third electrode of the fifth transistor and the first electrode of the second transistor.

[0015] Optionally, the nonlinear branch also includes a DC blocking capacitor and an adjustable bias resistor, and the DC blocking capacitor and the bias resistor are both coupled between the first electrode of the second transistor and the second output terminal of the primary linear amplifier, wherein the first electrode of the second transistor is coupled to an adjustable bias voltage through the bias resistor to adjust the DC voltage of the first electrode of the second transistor.

[0016] Optionally, the linear branch includes: a linear transconductance path, the linear transconductance path is used to receive the positive voltage signal and the negative voltage signal, and convert the positive voltage signal and the negative voltage signal into current signals and then output them;

[0017] A third resistor is coupled to the output end of the linear transconductance path to convert the current signal into a voltage signal, and the voltage signal is used as the driving signal.

[0018] Optionally, the nonlinear branch includes: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a first resistor, an adjustable capacitor, a first current source, a second current source and a current controller;

[0019] The first electrode of the first transistor is connected to the second output terminal of the primary linear amplifier, the second electrode of the first transistor is connected to the third electrode of the third transistor, and the second electrode and the first electrode of the third transistor are both connected to a power supply voltage or ground;

[0020] A first electrode of the fourth transistor is coupled to a fourth bias voltage, a second electrode of the fourth transistor is connected to an output end of the linear transconductance path, and the second electrode of the fourth transistor outputs the compensation signal, a third electrode of the fourth transistor is connected to a second electrode of the second transistor, and a first electrode of the second transistor is connected to a first output end of the primary linear amplifier;

[0021] A first electrode of the fifth transistor is coupled to a fifth bias voltage, a second electrode of the fifth transistor is connected to the power supply voltage or to ground, and a third electrode of the fifth transistor is connected to a third electrode of the fourth transistor and a second electrode of the second transistor;

[0022] The first resistor is connected in parallel with the adjustable capacitor, and both the first resistor and the adjustable capacitor are coupled between the third electrode of the second transistor and the third electrode of the first transistor;

[0023] The first current source is coupled to the third electrode of the first transistor, and the second current source is coupled to the third electrode of the second transistor;

[0024] The current controller is used to adjust the current value of the first current source and the current value of the second current source.

[0025] Optionally, the nonlinear branch includes: a second transistor, a fourth transistor, a fifth transistor, an adjustable capacitor, a first resistor, a bias resistor and a DC blocking capacitor;

[0026] The first electrode of the second transistor is connected to the first output terminal of the primary linear amplifier through the DC blocking capacitor, and the second electrode of the second transistor is connected to the third electrode of the fourth transistor;

[0027] A first electrode of the fourth transistor is coupled to a fourth bias voltage, a second electrode of the fourth transistor is connected to an output end of the linear transconductance path, and a second electrode of the fourth transistor is an output end of the nonlinear branch to output the compensation signal;

[0028] A first electrode of the fifth transistor is coupled to a fifth bias voltage, a second electrode of the fifth transistor is connected to the power supply voltage or ground, and a third electrode of the fifth transistor is connected to the third electrode of the fourth transistor and the second electrode of the second transistor;

[0029] The adjustable capacitor and the first resistor are both coupled to the third electrode of the second transistor;

[0030] The bias resistor is coupled between the first electrode of the second transistor and the adjustable bias voltage, and the bias resistor is connected to the DC blocking capacitor.

[0031] In the linear laser driving circuit provided by the present invention, the linear laser driving circuit includes a primary linear amplifier, a linear branch and a nonlinear branch, the nonlinear branch is used to receive the negative voltage signal output by the primary linear amplifier, and output a nonlinear compensation signal to compensate for the nonlinear effect of the laser, and the output end of the nonlinear branch is connected to the output end of the linear branch, so that the nonlinear compensation signal output by the nonlinear branch is superimposed on the driving signal output by the linear branch to form an output electrical signal. In this way, the nonlinearity in the output signal can compensate for the nonlinear effect of the laser itself, enhance the linearity of the optical signal output by the laser, and optimize the performance of the optical eye diagram. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a principle schematic diagram of a linear laser driving circuit in the prior art;

[0033] Figure 2 and Figure 3 It is a schematic diagram of the electrical eye diagram of the input voltage signal;

[0034] Figure 4 yes Figure 1 Schematic diagram of the optical eye diagram at sampling point z in;

[0035] Figure 5 is a schematic diagram of the principle of a linear laser driving circuit provided by an embodiment of the present invention;

[0036] Figure 6 yes Figure 5 Schematic diagram of the input electrical eye diagram of the sampling point x in;

[0037] Figure 7 yes Figure 5 Schematic diagram of the output electrical eye diagram of the sampling point y in;

[0038] Figure 8 yes Figure 5 Schematic diagram of the optical eye diagram at sampling point z in;

[0039] Fig. 9 A schematic diagram showing the circuit symbol for an N-type transistor;

[0040] Fig.10 A schematic diagram showing the circuit symbol for a P-type transistor;

[0041] Fig.11 A schematic diagram showing the circuit symbol of an NMOS tube;

[0042] Fig.12 A schematic diagram showing the circuit symbol of a PMOS tube;

[0043] Fig.13 and Fig.14 is a circuit diagram of a linear laser driving circuit provided by an embodiment of the present invention;

[0044] Fig.15 is a circuit diagram of another linear laser driving circuit provided by an embodiment of the present invention;

[0045] Fig.16 is a circuit diagram of another linear laser driving circuit provided by an embodiment of the present invention;

[0046] Fig.17 is a circuit diagram of another linear laser driving circuit provided by an embodiment of the present invention;

[0047] Fig.18 and 19 is a circuit diagram of another linear laser driving circuit provided by an embodiment of the present invention;

[0048] Fig. 20 is a circuit diagram of a linear laser driving circuit provided by another embodiment of the present invention;

[0049] Fig.21 is a circuit diagram of a linear laser driving circuit provided by another embodiment of the present invention;

[0050] Figure 22 to Figure 30 Schematic diagram of an eye diagram of a sampling point Vout of a linear laser driving circuit provided in different configurations according to an embodiment of the present invention.

[0051] In the figure,

[0052] 10-laser driver; 20-laser;

[0053] 110 - primary linear amplifier; 120 - linear branch; 121 - linear transconductance path; 130 - nonlinear branch; 131 - current controller; 140 - laser. DETAILED DESCRIPTION

[0054] The linear laser driving circuit proposed in the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0055] Figure 5It is a schematic diagram of the principle of a linear laser driving circuit provided by an embodiment of the present invention. Fig.13 is a circuit diagram of a linear laser driving circuit provided by an embodiment of the present invention. Figure 5 Combined with Fig.13 As shown, the linear laser driving circuit includes a primary linear amplifier 110 , a linear branch 120 , a nonlinear branch 130 and a laser 140 .

[0056] The primary linear amplifier 110 is used to amplify the input differential voltage signal and output the amplified differential voltage signal. The differential voltage signal output by the primary linear amplifier 110 serves as the input voltage signal of the linear branch 120 and the nonlinear branch 130. The differential voltage signal includes a positive voltage signal and a negative voltage signal. The primary linear amplifier 110 has a first output terminal and a second output terminal. The first output terminal is used to output the positive voltage signal of the differential voltage signal, and the second output terminal is used to output the negative voltage signal of the differential voltage signal.

[0057] The linear branch 120 is used to receive the differential voltage signal output by the primary linear amplifier and output a linear driving signal; the nonlinear branch 130 is used to receive the differential voltage signal output by the primary linear amplifier 110 and output a nonlinear compensation signal to compensate for the nonlinear effect of the laser 140. The output end of the nonlinear branch 130 is connected to the output end of the linear branch 120 so that the compensation signal is superimposed on the driving signal to form an output electrical signal. The output electrical signal is a voltage signal or a current signal, that is, the nonlinear branch is a pre-distortion branch, that is, the nonlinear branch can pre-distort the output electrical signal before the output electrical signal enters the laser. In this way, the nonlinear effect of the laser itself can be compensated, the linearity of the optical signal output by the laser can be enhanced, and the performance of the optical eye diagram can be optimized. That is to say, by pre-distorting the eye diagram of the electrical signal (voltage or current) output by the linear laser driving circuit, and then after the distortion caused by the nonlinearity of the laser, a correct eye diagram and better performance are generated, so that the eye diagram has a lower TDECQ value (Transmitter and Dispersion Eye Closure for PAM4, emission dispersion eye diagram closure four phases).

[0058] Specifically, the transmission signal function of the nonlinear signal branch can be expressed as B(x)=β1x+β2x 2 +β3x 3 +…β n x n .

[0059] The output signals of the linear signal branch and the nonlinear signal branch are superimposed (ie, the driving signal and the compensation signal are superimposed) and then output, and then drive the laser to generate an optical signal.

[0060] The mechanism of B(x) is to offset the nonlinear term in the laser C(y), so that the final output optical signal has good linearity and a correct eye diagram. The expression of the laser output optical signal z is as follows:

[0061] z=C(y)=c1y+c2y 2 +c3y 3 +…c n y n =c1(αx+β1x+β2x 2 +β3x 3 +…)+c2(αx+β1x+β2x 2 +β3x 3 +…) 2 +c3(αx+β1x+β2x 2 +β3x 3 +…) 3 +…≈c1(α+β1)x+[c1β2+c2(α+β1) 2 ]x 2 +[c1β3+2c2(α+β1)β2+c3(α+β1) 3 ]x 3

[0062] In the above derivation, the fourth-order and higher nonlinear coefficients are finally ignored because in actual situations, the values ​​of these high-order terms are small and have little effect on the overall performance. In order to make the final output linearity good, that is, z≈c1(α+β1)x, it is necessary to satisfy:

[0063] c1β2+c2(α+β1) 2 ≈0

[0064] c1β3+2c2(α+β1)β2+c3(α+β1) 3 ≈0

[0065] Wherein, C(y) represents the output optical signal of the laser; B(x) represents the compensation signal of the nonlinear signal branch; c1, c2, and c3 are all coefficients; α is the parameter of the specific device in the linear branch 120, such as the relevant electrical parameters (transconductance and resistance, etc.) of the transistor in the linear branch 120; β1, β2, β3.....β n They are all represented as parameters of specific devices in the nonlinear branch 130, such as relevant electrical parameters (transconductance and resistance, etc.) of transistors in the nonlinear branch 130, and n≥3.

[0066] In practical applications, for a specific nonlinear branch (determined by coefficients c1, c2, c3) and the gain of the linear branch 120 (determined by α), the above relationship can be established by adjusting the parameters β1, β2, β3 of the nonlinear branch 130.

[0067] Figure 6 yes Figure 5 Schematic diagram of the input electrical eye diagram of the sampling point x in; Figure 7 yes Figure 5 Schematic diagram of the output electrical eye diagram of the sampling point y in; Figure 8 yes Figure 5 Schematic diagram of the optical eye diagram of the sampling point z in Figures 6 to 8 It can be seen that at sampling point x, the linearity of the input differential voltage signal is good, and its input electrical eye diagram is also very linear, that is, the three eyes in the input electrical eye diagram are not skewed and the heights of the three eyes are consistent. At sampling point y, sampling point y is the output electrical signal generated by superimposing the driving signal of the linear branch and the compensation signal of the nonlinear branch. The compensation signal generated by the nonlinear branch 130 can cause the eye diagram of the output electrical signal to be pre-distorted, thereby compensating for the nonlinearity of the laser itself, and then offsetting the influence of the nonlinear distortion of the laser. Therefore, at sampling point z, that is, the optical signal output by the linear laser driving circuit, the optical eye diagram is corrected, that is, the linear laser driving circuit provided by this embodiment can correct the optical eye diagram, thereby improving the signal-to-noise ratio (SNR) of the sampling point and reducing the bit error rate (BER).

[0068] It should be noted that the transistors involved in the following embodiments of the present invention may be triodes (Bipolar Transistor, also known as bipolar junction transistors) or field effect transistors (such as metal oxide semiconductor tubes (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET), etc., and this embodiment does not limit the type of transistors. Among them, transistors can be divided into N-type transistors and P-type transistors. For example, Figure 8 and Fig. 9 They are the circuit symbol schematics of N-type transistor (NPN) and P-type transistor (PNP); Fig.10 and Fig.11 Schematic diagrams of circuit symbols for N-type MOSFET (NMOS) and P-type MOSFET (PMOS). The N-type transistor can be an N-type triode (NPN) or an N-type MOSFET (NMOS), and the P-type transistor can be a P-type triode (PNP) or a P-type MOSFET (PMOS). The nonlinearity of these transistors will also vary with their bias states. For example, when the bias current is large, the nonlinearity is weaker, and when the bias current is small, the nonlinearity is stronger.

[0069] For ease of description, in the embodiment, when the transistor is a triode, the first electrode is used to represent the base (B), the second electrode is used to represent the collector (C), and the third electrode is used to represent the emitter (E); when the transistor is a field effect transistor, the first electrode is used to represent the gate (G), and the second electrode and the third electrode are used to represent the drain (D) and the source (S) and one of them respectively. The drawings in the following embodiments of the present application use triodes as transistors as examples to exemplify various circuits. Among them, the transistor refers to all transistors in the linear branch 120 and the nonlinear branch 130.

[0070] Fig.13 FIG. 1 is a circuit diagram of a linear laser driving circuit provided by an embodiment of the present invention. Fig.13 As shown, after the input differential voltage signal Vin is input to the primary linear amplifier 110, the primary linear amplifier 110 can amplify the input differential voltage signal and output the differential voltage signal. The differential voltage signal output by the primary linear amplifier 110 includes a positive voltage signal +0.5pVin and a negative voltage signal -0.5pVin. The primary linear amplifier 110 has a first output terminal and a second output terminal. The first output terminal of the primary linear amplifier 110 outputs a positive voltage signal, and the second output terminal of the primary linear amplifier 110 outputs a negative voltage signal.

[0071] The linear branch 120 includes a first transistor Q1 and an adjustable first resistor R1, that is, the linear branch 120 is an emitter follower branch. Specifically, the first electrode of the first transistor Q1 is connected to the output end of the primary linear amplifier 110, specifically the first output end, to input the forward voltage signal, the third electrode of the first transistor Q1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is the output end of the linear branch 120 to output the drive signal, and the other end of the first resistor R1 is connected to the output end of the nonlinear branch 130.

[0072] like Fig.13 As shown, when the first transistor Q1 is an N-type transistor, the second electrode of the first transistor Q1 is connected to the power supply voltage.

[0073] like Fig.14 As shown, when the first transistor Q1 is a P-type transistor, the second electrode of the first transistor Q1 is grounded.

[0074] Continue to refer Fig.13As shown, the nonlinear branch 130 includes a second transistor Q2 and an adjustable second resistor R2, wherein the first electrode of the second transistor Q2 is connected to the output end of the primary linear amplifier 110, specifically the second output end, to input the negative voltage signal, the second electrode of the second transistor Q2 is connected to the first resistor R1, and the third electrode of the second transistor Q2 is connected to the second resistor R2, wherein the second electrode of the second transistor Q2 is the output end of the nonlinear branch 130 to output the compensation signal.

[0075] Optional, such as Fig.13 As shown, when the second transistor Q2 is an N-type transistor, the second transistor Q2 is grounded through the second resistor R2.

[0076] like Fig.14 As shown, when the second transistor Q2 is a P-type transistor, the second transistor Q2 is connected to the power supply voltage VDD through the second resistor R2.

[0077] The compensation signal outputted from the output end of the nonlinear branch 130 is superimposed on the driving signal outputted from the output end of the linear branch 120 and is transmitted to the laser, specifically, to the load impedance of the laser.

[0078] The voltage across the load impedance of the laser is related by:

[0079]

[0080] If gm1*R1>5, then

[0081]

[0082] If R2 is adjusted so that gm2*R2>5, then

[0083]

[0084] Where Vout is the voltage on the load impedance of the laser (i.e. Fig.14 pVin represents the voltage value of the forward voltage signal; gm1 represents the transconductance of the first transistor Q1; R1 represents the resistance value of the first resistor R1; R L represents the resistance value of the load impedance of the laser; gm2 represents the transconductance of the second transistor Q2; R2 represents the resistance value of the second resistor R2.

[0085] Since the response of the laser diode in the laser is mainly determined by the load impedance ratio, and the load impedance is usually a linear device, the nonlinear branch 130 has little effect. If the resistance value of the second resistor R2 is adjusted so that the transconductance of the second transistor Q2 and the resistance value of the resistor are less than or equal to 1, that is, gm2*R2<<1; wherein gm2 is the transconductance of the second transistor Q2, and R2 is the resistance value of the second resistor R2.

[0086] Furthermore, the relationship between the voltage on the load impedance of the laser is as follows:

[0087]

[0088] Combined with the above relationship, it can be known that since the second resistor R2 is coupled to the third electrode of the second transistor Q2, that is, the second resistor R2 is a degenerate resistor of the third electrode of the second transistor Q2, the strength of the nonlinear branch 130 can be adjusted by adjusting the resistance value of the second resistor R2. The strength of the nonlinear branch 130 refers to the magnitude of the current in the nonlinear branch 130, the amplitude of the voltage, or the signal characteristics (such as frequency and phase, etc.) generated by the nonlinear branch 130.

[0089] Fig.15 FIG. 1 is a circuit diagram of another linear laser driving circuit provided by an embodiment of the present invention. Fig.15 In the embodiment, the structure of the linear branch 120 is the same as that of the linear branch 120 in the above embodiment, and will not be repeated here.

[0090] like Fig.15 As shown, the structure of the nonlinear branch 130 is similar to that of the above-mentioned Fig.13 The structure of the nonlinear branch 130 in the embodiment is different. Specifically, the nonlinear branch 130 includes a second transistor Q2, a third transistor Q3 and an adjustable second resistor R2, the first electrode of the second transistor Q2 is connected to the second output terminal of the primary linear amplifier 110 to input the negative voltage signal, the first electrode of the third transistor is connected to the first bias voltage VCAS1, the second electrode of the third transistor Q3 is connected to the first resistor R1, the third electrode of the third transistor Q3 is connected to the second electrode of the second transistor Q2, and the third electrode of the second transistor Q2 is connected to the second resistor R2, wherein the second electrode of the third transistor Q3 is the output terminal of the nonlinear branch 130 to output the compensation signal.

[0091] Specifically, the third transistor Q3 is used to reduce the first pole DC voltage of the second transistor Q2, thereby increasing the DC voltage upper limit of the output terminal of the nonlinear branch 130, thereby increasing the reliability of the second transistor Q2. At the same time, the third transistor Q3 can also effectively reduce the equivalent capacitance observed from the first pole of the second transistor Q2, thereby optimizing the influence of the Maitreya effect capacitor. It should be noted that the observed equivalent capacitance from the first pole of the second transistor Q2 includes the comprehensive effect of the barrier capacitance, diffusion capacitance and other parasitic capacitances of the internal PN junction of the second transistor Q2. The capacitance value of the observed equivalent capacitance from the first pole of the second transistor Q2 will change with the operating state of the second transistor Q2 (such as bias voltage or current, etc.) and the configuration of the external circuit.

[0092] refer to Fig.16 As shown, in Fig.15 On the basis of the nonlinear branch 130 shown, the nonlinear branch 130 may further include a fourth transistor Q4, the fourth transistor Q4 is coupled between the power supply voltage VDD and the third transistor Q3, and the third electrode of the fourth transistor Q4 is connected to the third electrode of the third transistor Q3 and the second electrode of the second transistor Q2.

[0093] like Fig.16 As shown, when the fourth transistor Q4 is an N-type transistor, the second electrode of the fourth transistor Q4 is connected to the power supply voltage VDD. When the fourth transistor Q4 is a P-type transistor, the second electrode of the fourth transistor Q4 is grounded.

[0094] Further, the first electrode of the third transistor Q3 is connected to the first bias voltage VCAS1, and the first electrode of the fourth transistor Q4 is connected to the second bias voltage VCAS2. By adjusting the voltage value of the first bias voltage VCAS1 and the voltage value of the second bias voltage VCAS2, the current distribution ratio between the third transistor and the fourth transistor Q4 can be changed, thereby changing the gain of the nonlinear branch 130. In addition, the combination of the third transistor Q3 and the fourth transistor Q4 increases additional adjustment freedom.

[0095] like Fig.17 As shown, in Fig.16On the basis of the nonlinear branch shown, the nonlinear branch may further include a fifth transistor Q5 and a fifth current source I5, wherein the fifth transistor Q5 is coupled between the first electrode of the second transistor Q2 and the second output terminal of the primary linear amplifier 110, the first electrode of the fifth transistor Q5 is connected to the second output terminal of the primary linear amplifier 110, the third electrode of the fifth transistor Q5 is connected to the first electrode of the second transistor Q2, and the fifth current source I5 is coupled between the third electrode of the fifth transistor Q5 and the first electrode of the second transistor Q2.

[0096] Optionally, the fifth transistor Q5 is an N-type transistor, and the second electrode of the fifth transistor Q5 is connected to the power supply voltage. The fifth transistor Q5 is a P-type transistor, and the second electrode of the fifth transistor Q5 is grounded.

[0097] In this embodiment, the fifth transistor Q5 and the fifth current source I5 constitute an emitter follower to realize the function of DC level conversion, so as to provide a more suitable DC level to the second transistor Q2, and then stably provide the required DC level to the second transistor Q2, thereby optimizing the working performance of the entire nonlinear branch. In addition, by setting the fifth transistor Q5 and the fifth current source I5, the response speed to the high-speed signal in the nonlinear branch 130 can be enhanced, and the driving ability of the high-speed signal in the nonlinear branch 130 can be improved, so that the nonlinear branch can have more stable and efficient performance when processing high-frequency or rapidly changing signals.

[0098] like Fig.18 As shown, in Fig.16 On the basis of the nonlinear branch 130 shown, the nonlinear branch 130 may further include a DC blocking capacitor CB and an adjustable bias resistor RB, wherein the DC blocking capacitor CB and the bias resistor RB are both coupled between the first electrode of the second transistor Q2 and the second output terminal of the primary linear amplifier 110 .

[0099] The blocking capacitor CB and the bias resistor RB are used to isolate the DC level of the first electrode of the second transistor Q2 from the previous stage, so that the DC voltage of the first electrode of the second transistor Q2 can be freely controlled by adjusting the adjustable bias voltage, which is conducive to optimizing the stability and flexibility of the nonlinear branch 130. In addition, the blocking capacitor CB and the bias resistor RB can also determine the high-pass corner frequency of high-speed signal transmission. By adjusting the resistance value of the bias resistor RB, the signal energy transmission of different frequencies can be adjusted, thereby optimizing the high-speed performance. In addition, the DC current of the second transistor Q2 can be adjusted by adjusting the adjustable bias voltage VB, thereby adjusting the nonlinear characteristics in the transconductance (gm2) of the second transistor Q2.

[0100] like Fig.18 As shown, when the transistors in the nonlinear branch 130 are all N-type transistors, the first electrode of the fourth transistor Q4 is connected to the power supply voltage, the first electrode of the first transistor Q1 is connected to the power supply voltage VDD, and one end of the second resistor R2 is grounded.

[0101] like Fig.19 As shown, when all transistors in the nonlinear branch 130 are P-type transistors, the first electrode of the fourth transistor Q4 is grounded, the first electrode of the first transistor Q1 is grounded, and the third electrode of the second transistor Q2 is connected to the power supply voltage VDD through the second resistor R2.

[0102] The present invention also provides another linear laser driving circuit. Fig. 20 As shown, the linear laser driving circuit includes a primary linear amplifier 110 , a linear branch 120 and a nonlinear branch 130 .

[0103] like Fig. 20 As shown, after the differential voltage signal Vin is input into the primary linear amplifier 110, the primary linear amplifier 110 can amplify the input differential voltage signal and then output it, thereby outputting a positive voltage signal +0.5pVin and a negative voltage signal -0.5pVin.

[0104] like Fig. 20 As shown, the linear branch 120 includes a linear transconductance path 121 and a third resistor R3. Specifically, the linear transconductance path 121 is used to receive the positive voltage signal and the negative voltage signal, and convert the positive voltage signal and the negative voltage signal into current signals and then output them. Specifically, the linear transconductance path 121 has two input terminals, namely a positive input terminal and a negative input terminal. The positive input terminal of the linear transconductance path 121 is connected to the positive output terminal of the primary linear amplifier 110, and the negative input terminal of the linear transconductance path 121 is connected to the negative output terminal of the primary linear amplifier 110.

[0105] The third resistor R3 is coupled to the output end of the linear transconductance path 121, that is, the third resistor R3 serves as a load resistor of the linear transconductance path 121 to convert the current signal into a voltage signal, and the voltage signal serves as the driving signal. In addition, the third resistor R3 is also coupled to the output end of the nonlinear branch 130, that is, the third resistor R3 serves as a load resistor of the linear transconductance path 121 and the nonlinear branch 130, so that not only the current signal output by the linear transconductance path 121 can be converted into a voltage signal, but also the output impedance can be matched.

[0106] like Fig. 20As shown, the nonlinear branch 130 includes a second transistor Q2, a third transistor Q3, a fourth transistor Q4, a fifth transistor Q5, an adjustable capacitor C1, a first resistor R1 and a bias resistor RB.

[0107] The first electrode of the second transistor Q2 is connected to the first output terminal of the primary linear amplifier 110 through the DC blocking capacitor CB.

[0108] The second electrode of the second transistor Q2 is connected to the third electrode of the fourth transistor Q4, the second electrode of the fourth transistor Q4 is connected to the output end of the linear transconductance path 121, the second electrode of the fourth transistor Q4 is connected to the output end of the linear transconductance path 121, and the second electrode of the fourth transistor Q4 is the output end of the nonlinear branch 130 to output the compensation signal.

[0109] The third electrode of the fifth transistor Q5 is connected to the third electrode of the fourth transistor Q4 and the second electrode of the second transistor Q2, wherein the first electrode of the fifth transistor Q5 is coupled to the fifth bias voltage VCAS5, and the first electrode of the fourth transistor Q4 is coupled to the fourth bias voltage VCAS4. In this way, the proportion of the current in the nonlinear branch 130 flowing to the third transistor Q3 can be adjusted by adjusting the voltage value of the fourth bias voltage VCAS5 and the voltage value of the fifth bias voltage VCAS5, thereby changing the overall gain of the nonlinear branch 130.

[0110] In this embodiment, when the fifth transistor Q5 is an N-type transistor, the second electrode of the fifth transistor is connected to the power supply voltage VDD. When the fifth transistor Q5 is a P-type transistor, the second electrode of the fifth transistor is grounded. Fig. 20 The fifth transistor Q5 shown in FIG. 1 is an N-type transistor as an example.

[0111] The adjustable capacitor C1 and the first resistor R1 are both coupled to the third electrode of the second transistor Q2. By reducing the resistance of the first resistor R1, the nonlinear characteristics of the nonlinear branch 130 can be enhanced. By increasing the capacitance of the adjustable capacitor C1, the nonlinearity of the high-frequency signal component can be enhanced.

[0112] The bias resistor RB is coupled between the first pole of the second transistor Q2 and the adjustable bias voltage VB, and the bias resistor RB is connected to the DC blocking capacitor CB, that is, the nonlinear branch 130 adopts a single-ended input in an AC coupling mode composed of the DC blocking capacitor CB and the bias resistor RB. In addition, the first pole of the second transistor Q2 is coupled to the adjustable bias voltage VB through the bias resistor RB, so that the DC blocking capacitor CB and the bias resistor RB can isolate the DC voltage of the first pole of the second transistor Q2 from the front-stage circuit, and the DC voltage and DC current of the first pole of the second transistor Q2 can be freely adjusted by adjusting the adjustable bias voltage VB, so that the nonlinear characteristics in the transconductance of the second transistor Q2 can be adjusted. In other words, the intensity of the pre-distortion can be freely adjusted, thereby adapting to different models of lasers (different models of lasers have different nonlinearities) and different operating temperatures (when the laser temperature changes, the nonlinearity will also change to a certain extent).

[0113] In addition, the DC blocking capacitor CB and the bias resistor RB can also determine the high-pass corner frequency of the high-speed signal transmission in the nonlinear branch 130. The resistance value of the bias resistor RB can be adjusted according to actual needs, thereby adjusting the signal energy transmission of different frequencies, thereby optimizing the high-speed performance.

[0114] In further schemes, such as Fig. 20 As shown, the nonlinear branch 130 may further include a third current source I3, which is an adjustable current source. The third current source I3 is coupled to the output end of the nonlinear branch 130 and the output end of the linear branch 120, and the third current source I3 is used to compensate for the DC current output by the linear branch 120 and the nonlinear branch 130 to compensate for the DC current input into the laser 140.

[0115] The present invention also provides another linear laser driving circuit. Fig.21 As shown, the linear laser driving circuit includes a primary linear amplifier 110 , a nonlinear branch 130 and a linear branch 120 .

[0116] like Fig.21 As shown, after the differential voltage signal Vin is input into the primary linear amplifier 110, the primary linear amplifier 110 can amplify the input differential voltage signal and then output it, thereby outputting a positive voltage signal +0.5pVin and a negative voltage signal -0.5pVin.

[0117] It should be noted that Fig.21 The linear branch shown is Fig. 20 The structure of the linear branch described in is the same as that in Fig.21 The nonlinear branch shown is Fig. 20 The structure of the nonlinear branch described in is different.

[0118] like Fig.21 As shown, the nonlinear branch 130 includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a fourth transistor Q4, a fifth transistor Q5, a first resistor R1, an adjustable capacitor C1, a first current source I1, a second current source I2 and a current controller 131, the first electrode of the first transistor is connected to the second output end of the primary linear amplifier, and the second electrode of the first transistor Q1 is connected to the third electrode of the third transistor Q3.

[0119] The second electrode of the fourth transistor Q4 is connected to the output end of the linear transconductance path 121, and the second electrode of the fourth transistor Q4 outputs the compensation signal, the third electrode of the fourth transistor Q4 is connected to the second electrode of the second transistor Q2, and the first electrode of the second transistor Q2 is connected to the first output end of the primary linear amplifier.

[0120] The second electrode of the fifth transistor Q5 is connected to the power supply voltage or ground, and the third electrode of the fifth transistor Q5 is connected to the third electrode of the fourth transistor Q4 and the second electrode of the second transistor Q2. The first electrode of the fourth transistor Q4 is coupled to the fourth bias voltage VCAS4, and the first electrode of the fifth transistor Q5 is coupled to the fifth bias voltage VCAS5. By adjusting the fourth bias voltage VCAS4 and the fifth bias voltage VCAS5, the proportion of the branch current flowing to the third transistor Q3 can be adjusted, so that the overall gain of the nonlinear branch 130 can be changed.

[0121] Optionally, when the transistors in the nonlinear branch are all N-type transistors, the second electrode and the first electrode of the third transistor Q3 and the first electrode of the fifth transistor Q5 are connected to the power supply voltage VDD, and the second electrode of the fourth transistor Q4 is connected to the power supply voltage VDD through the third resistor R3.

[0122] When the transistors in the nonlinear branch are all P-type transistors, the second electrode and the first electrode of the third transistor Q3 and the first electrode of the fifth transistor Q5 are grounded, and the second electrode of the fourth transistor Q4 is grounded through the third resistor R3.

[0123] The first resistor R1 is connected in parallel with the adjustable capacitor C1, and both the first resistor R1 and the adjustable capacitor C1 are coupled between the third electrode of the second transistor Q2 and the third electrode of the first transistor Q1.

[0124] The first current source is coupled to the third electrode of the first transistor Q1 , and the second current source is coupled to the third electrode of the second transistor Q2 .

[0125] In this embodiment, the current controller 131 is used to adjust the current value of the first current source I1 and the current value of the second current source I2. The current value of the first current source I1 and the current value of the second current source I2 are related by the following equation:

[0126] I1=(1+γ)*I S ; I2=(1-γ)*I S ;

[0127] Wherein, I1 represents the current value of the first current source; I2 represents the current value of the second current source; I S It is represented as a fixed current value; γ is represented as a control coefficient, and -1<γ<1;

[0128] According to the above relationship, when the control coefficient γ=0, the smaller (or weaker) the nonlinearity of the nonlinear branch 130 is, and the closer |γ| is to 1, the stronger the nonlinearity of the nonlinear branch 130 is. Therefore, by regulating the current value of the first current source I1 and the current value of the second current source I2 through the current controller 131, the nonlinear strength of the nonlinear branch 130 can be adjusted.

[0129] In the nonlinear branch 130 of the present embodiment, the nonlinear branch 130 adopts a smaller bias current design to enhance the nonlinear characteristics of the nonlinear branch 130. In practical applications, the additional current consumed by the nonlinear branch 130 accounts for about 5% to 10% of the total current, so it will not significantly increase the overall power consumption of the system. On the contrary, when the nonlinear branch 130 is turned on, the DSP of the front stage of the system can reduce the intensity of its DPD (digital pre-distortion), thereby reducing the overall power consumption of the system and further reducing the cost.

[0130] In a further solution, the linear laser driving circuit further includes a capacitor C, which is a DC blocking capacitor and is coupled to output ends of the linear branch 120 and the nonlinear branch 130 .

[0131] In this embodiment, the superimposed output electrical signal of the linear branch 120 of the nonlinear branch 130 is output to the laser 140, which is a linear laser. The laser 140 includes a laser diode and a load impedance. The laser diode is used to convert electrical energy into laser light. In order to better illustrate the inventive point of the present invention, the description and illustration of the laser diode are omitted. The laser can be a VCSEL (vertical cavity surface emitting laser), a DFB (distributed feedback laser), an EML (electroabsorption modulated laser) or an MZM (Mach-Zehnder modulator).

[0132] Figure 22 to Figure 30Schematic diagram of the eye diagram of the output end of the laser of the linear laser driving circuit provided by the embodiment of the present invention under different configurations. Figure 22 to Figure 30 The horizontal axis is time, and the vertical axis is the voltage of the sampling point Vout. Fig. 22 Based on Fig.13 Eye diagram diagram of the sampling point Vout in the linear laser driving circuit. Figure 23 to Figure 26 Based on Fig.13 The eye diagram of the sampling point Vout of the nonlinear branch in the linear laser driving circuit under different configurations is shown in FIG. Figure 23 to Figure 26 It can be seen that adjusting different configurations in the nonlinear branch can make the sampling point Vout have different eye diagram effects, that is, the nonlinear branch can produce different pre-distortions. Figure 27 to Figure 30 All are based on Fig.21 Schematic diagram of the eye diagram of the sampling point Vout in the linear laser driving circuit, where: Fig. 27 The eye diagram is a schematic diagram of the eye diagram when the nonlinear branch is closed. Figure 28 to Figure 30 is the eye diagram of Vout at the sampling point when the nonlinear branch is turned on, and Figure 28 to Figure 30 The eye diagrams under different distortion configurations are compared. Figure 27 to Figure 30 It can be seen that when the nonlinear branch is turned on, the eye diagram of the sampling point Vout will have characteristics such as falling edge acceleration, and the eye diagram of the sampling point Vout will be distorted, that is, a pre-distortion effect can be produced, thereby compensating for the nonlinearity of the laser itself.

[0133] In summary, in the linear laser driving circuit provided by the present invention, the linear laser driving circuit includes a primary linear amplifier, a linear branch and a nonlinear branch, the nonlinear branch is used to receive the negative voltage signal output by the primary linear amplifier, and output a nonlinear compensation signal to compensate for the nonlinear effect of the laser, and the output end of the nonlinear branch is connected to the output end of the linear branch, so that the compensation signal output by the nonlinear branch is superimposed on the driving signal output by the linear branch to form an output electrical signal. In this way, the nonlinear effect of the laser itself can be compensated, the linearity of the optical signal output by the laser can be enhanced, and the performance of the optical eye diagram can be optimized.

[0134] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A linear laser driving circuit, characterized in that: include: A primary linear amplifier, used to amplify an input differential voltage signal and output the amplified differential voltage signal, wherein the differential voltage signal includes a positive voltage signal and a negative voltage signal; A linear branch, used for receiving the differential voltage signal output by the primary linear amplifier and outputting a linear driving signal; A nonlinear branch is used to receive the differential voltage signal output by the primary linear amplifier and output a nonlinear compensation signal to compensate for the nonlinear effect of the laser. The output end of the nonlinear branch is connected to the output end of the linear branch so that the compensation signal is superimposed on the drive signal to form an output electrical signal, and the output electrical signal is provided to the laser to convert the output electrical signal into an optical signal.

2. The linear laser driving circuit according to claim 1, characterized in that: The linear branch comprises: A first transistor and an adjustable first resistor, wherein the first electrode of the first transistor is connected to the first output end of the primary linear amplifier to input the forward voltage signal, the second electrode of the first transistor is connected to the power supply voltage or ground, the third electrode of the first transistor is connected to one end of the first resistor, the other end of the first resistor is the output end of the linear branch to output the drive signal, and the other end of the first resistor is connected to the output end of the nonlinear branch.

3. The linear laser driving circuit according to claim 2, characterized in that: The nonlinear branch includes: a second transistor and an adjustable second resistor, wherein the first electrode of the second transistor is connected to the second output terminal of the primary linear amplifier to input the negative voltage signal, the second electrode of the second transistor is connected to the first resistor, and the third electrode of the second transistor is connected to the second resistor, wherein the second electrode of the second transistor is the output terminal of the nonlinear branch to output the compensation signal.

4. The linear laser driving circuit according to claim 2, characterized in that: The nonlinear branch includes: a second transistor, a third transistor and an adjustable second resistor, wherein the first electrode of the second transistor is connected to the second output terminal of the primary linear amplifier to input the negative voltage signal, the first electrode of the third transistor is connected to the first bias voltage, the second electrode of the third transistor is connected to the first resistor, the third electrode of the third transistor is connected to the second electrode of the second transistor, and the third electrode of the second transistor is connected to the second resistor, wherein the second electrode of the third transistor is the output terminal of the nonlinear branch to output the compensation signal.

5. The linear laser driving circuit according to claim 4, characterized in that: The nonlinear branch also includes a fourth transistor, which is coupled between the power supply voltage and the third transistor, wherein a first electrode of the fourth transistor is connected to a second bias voltage, a second electrode of the fourth transistor is connected to the power supply voltage or to ground, and a third electrode of the fourth transistor is connected to a third electrode of the third transistor and a second electrode of the second transistor.

6. The linear laser driving circuit according to claim 5, characterized in that: The nonlinear branch also includes a fifth transistor and a fifth current source. The fifth transistor is coupled between the first electrode of the second transistor and the second output terminal of the primary linear amplifier. The first electrode of the fifth transistor is connected to the second output terminal of the primary linear amplifier. The second electrode of the fifth transistor is connected to the power supply voltage or ground. The third electrode of the fifth transistor is connected to the first electrode of the second transistor. The fifth current source is coupled between the third electrode of the fifth transistor and the first electrode of the second transistor.

7. The linear laser driving circuit according to claim 5, characterized in that: The nonlinear branch also includes a DC blocking capacitor and an adjustable bias resistor, wherein the DC blocking capacitor and the bias resistor are both coupled between the first electrode of the second transistor and the second output terminal of the primary linear amplifier, wherein the first electrode of the second transistor is coupled to the adjustable bias voltage through the bias resistor to adjust the DC voltage of the first electrode of the second transistor.

8. The linear laser driving circuit according to claim 1, characterized in that: The linear branch comprises: A linear transconductance path, wherein the linear transconductance path is used to receive the positive voltage signal and the negative voltage signal, and convert the positive voltage signal and the negative voltage signal into current signals and then output them; A third resistor is coupled to the output end of the linear transconductance path to convert the current signal into a voltage signal, and the voltage signal is used as the driving signal.

9. The linear laser driving circuit according to claim 8, characterized in that: The nonlinear branch includes: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a first resistor, an adjustable capacitor, a first current source, a second current source and a current controller; The first electrode of the first transistor is connected to the second output terminal of the primary linear amplifier, the second electrode of the first transistor is connected to the third electrode of the third transistor, and the second electrode and the first electrode of the third transistor are both connected to a power supply voltage or ground; A first electrode of the fourth transistor is coupled to a fourth bias voltage, a second electrode of the fourth transistor is connected to an output end of the linear transconductance path, and the second electrode of the fourth transistor outputs the compensation signal, a third electrode of the fourth transistor is connected to a second electrode of the second transistor, and a first electrode of the second transistor is connected to a first output end of the primary linear amplifier; A first electrode of the fifth transistor is coupled to a fifth bias voltage, a second electrode of the fifth transistor is connected to the power supply voltage or to ground, and a third electrode of the fifth transistor is connected to a third electrode of the fourth transistor and a second electrode of the second transistor; The first resistor is connected in parallel with the adjustable capacitor, and both the first resistor and the adjustable capacitor are coupled between the third electrode of the second transistor and the third electrode of the first transistor; The first current source is coupled to the third electrode of the first transistor, and the second current source is coupled to the third electrode of the second transistor; The current controller is used to adjust the current value of the first current source and the current value of the second current source.

10. The linear laser driving circuit according to claim 8, characterized in that: The nonlinear branch includes: a second transistor, a fourth transistor, a fifth transistor, an adjustable capacitor, a first resistor, a bias resistor and a DC blocking capacitor; The first electrode of the second transistor is connected to the first output terminal of the primary linear amplifier through the DC blocking capacitor, and the second electrode of the second transistor is connected to the third electrode of the fourth transistor; A first electrode of the fourth transistor is coupled to a fourth bias voltage, a second electrode of the fourth transistor is connected to an output end of the linear transconductance path, and a second electrode of the fourth transistor is an output end of the nonlinear branch to output the compensation signal; A first electrode of the fifth transistor is coupled to a fifth bias voltage, a second electrode of the fifth transistor is connected to the power supply voltage or ground, and a third electrode of the fifth transistor is connected to the third electrode of the fourth transistor and the second electrode of the second transistor; The adjustable capacitor and the first resistor are both coupled to the third electrode of the second transistor; The bias resistor is coupled between the first electrode of the second transistor and the adjustable bias voltage, and the bias resistor is connected to the DC blocking capacitor.

Images