Linear laser driving circuit

Abstract

The present invention provides a linear laser driving circuit, comprising a primary linear amplifier, a linear branch, and a non-linear branch. The non-linear branch is used for receiving a differential voltage signal output by the primary linear amplifier, and outputting a non-linear compensation signal to compensate for a non-linear effect of a laser, and an output terminal of the non-linear branch is connected to an output terminal of the linear branch, such that the compensation signal output by the non-linear branch and a driving signal output by the linear branch are superposed, to form an output electrical signal. In this way, the non-linear effect of the laser can be compensated for, the linearity of the optical signal output by the laser can be enhanced, and the performance of an optical eye pattern can be optimized.

Description

Linear laser drive circuit Technical Field

[0001] This invention relates to the field of circuit technology, and in particular to a linear laser driving circuit. Background Technology

[0002] In a linear optical communication system, as shown in Figure 1, the input voltage signal is first processed by a linear laser driver 10. The signal output by the laser driver 10 is a linearly amplified or reduced signal of the input voltage signal. After passing through the laser driver 10, the input voltage signal generates a voltage signal or a current signal to drive the laser 20, thereby converting the voltage signal or current signal into an optical signal, which is then transmitted through an optical coupler or optical fiber. However, due to the nonlinear characteristics of the laser itself, the nonlinearity introduces distortion during the conversion process, specifically manifested as skewness or inconsistent eye height in the optical eye diagram of the output optical signal.

[0003] As shown in Figures 2 and 3, under ideal linearity of the laser driver, the input voltage signal has 4 levels (referred to as 0 / 1 / 2 / 3 levels). The superposition of multiple periodic signals forms the eye diagram shown in Figures 2 and 3. In Figure 3, the arrows indicate the height of each eye (the height of the eyes is consistent under ideal linearity) and the sampling position of the eye (the sampling position of the eyes is also consistent under ideal linearity).

[0004] If the linearity of the laser driver 10 is good, the eye diagram of the output signal will also be very linear, with all three eyes being straight and at the same height. However, as shown in Figure 4, which is the optical eye diagram of the laser output (i.e., the optical eye diagram of sampling point z in Figure 1), due to the nonlinearity of the laser itself, the final output optical eye diagram may be skewed or have inconsistent eye heights. Since the final sampling can only be performed at a fixed eye diagram position, eye diagram skewness and / or inconsistent eye heights will prevent the three eyes from sampling at the optimal sampling point simultaneously, leading to an increase in communication error rate and a decrease in communication sensitivity. In the prior art, the linearity 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 cannot compensate for the optical eye diagram distortion caused by the nonlinearity of the laser, resulting in a skewed optical eye diagram, or the laser driver has a certain nonlinearity compensation capability, but it cannot be freely adjusted and cannot be adapted to different types of lasers and different operating temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a linear laser driving circuit to counteract the nonlinear effects 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 objectives, the present invention provides a linear laser driving circuit, comprising:

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

[0008] A linear branch is used to receive the differential voltage signal output by the primary linear amplifier and output a linear drive 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 terminal of the nonlinear branch is connected to the output terminal of the linear branch so that the compensation signal is superimposed with the driving 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 terminal of the first transistor is connected to the first output terminal of the primary linear amplifier to input the positive voltage signal, the second terminal of the first transistor is connected to the power supply voltage or ground, the third terminal of the first transistor is connected to the first terminal of the first resistor, the second terminal of the first resistor is the output terminal of the linear branch to output the drive signal, and the second terminal of the first resistor is connected to the output terminal of the nonlinear branch.

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

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

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

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

[0016] Optionally, the linear branch includes a linear transconductance path, which 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 a current signal and then output it.

[0017] A third resistor is coupled to the output of the linear transconductance path to convert the current signal into a voltage signal, which serves 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 terminal of the first transistor is connected to the second output terminal of the primary linear amplifier, and the second terminal of the first transistor is connected to the third terminal of the third transistor. Both the second and first terminals of the third transistor are connected to the power supply voltage or ground.

[0020] The first terminal of the fourth transistor is coupled to the fourth bias voltage, the second terminal of the fourth transistor is connected to the output terminal of the linear transconductance path, and the second terminal of the fourth transistor outputs the compensation signal. The third terminal of the fourth transistor is connected to the second terminal of the second transistor, and the first terminal of the second transistor is connected to the first output terminal of the primary linear amplifier.

[0021] The first terminal of the fifth transistor is coupled to the fifth bias voltage, the second terminal of the fifth transistor is connected to the power supply voltage or ground, and the third terminal of the fifth transistor is connected to the third terminal of the fourth transistor and the second terminal of the second transistor.

[0022] The first resistor and the adjustable capacitor are connected in parallel, and both the first resistor and the adjustable capacitor are coupled between the third terminal of the second transistor and the third terminal of the first transistor.

[0023] The first terminal of the first current source is coupled to the third terminal of the first transistor and the second terminal of the first current source is connected to the power supply voltage or ground. The first terminal of the second current source is coupled to the third terminal of the second transistor and the second terminal of the second current source is connected to the power supply voltage or ground.

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

[0027] The first terminal of the fourth transistor is coupled to the fourth bias voltage, the second terminal of the fourth transistor is connected to the output terminal of the linear transconductance path, and the second terminal of the fourth transistor is the output terminal of the nonlinear branch to output the compensation signal.

[0028] The first terminal of the fifth transistor is coupled to the fifth bias voltage, the second terminal of the fifth transistor is connected to the power supply voltage or ground, and the third terminal of the fifth transistor is connected to the third terminal of the fourth transistor and the second terminal of the second transistor.

[0029] The adjustable capacitor and the first resistor are both coupled between the third terminal of the second transistor and ground;

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

[0031] In the linear laser driving circuit provided by this invention, the linear laser driving circuit includes a primary linear amplifier, a linear branch, and a nonlinear branch. The nonlinear branch receives the negative voltage signal output by the primary linear amplifier and outputs a nonlinear compensation signal to compensate for the nonlinear effect of the laser. The output terminal of the nonlinear branch is connected to the output terminal of the linear branch, so that the nonlinear compensation signal output by the nonlinear branch is superimposed with 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 laser output optical signal, and optimize the performance of the optical eye diagram. Attached Figure Description

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

[0033] Figures 2 and 3 are schematic diagrams of the electro-optical representation of the input voltage signal;

[0034] Figure 4 is a schematic diagram of the optical eye diagram of sampling point z in Figure 1;

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

[0036] Figure 6 is a schematic diagram of the input photoelectric sensor at sampling point x in Figure 5;

[0037] Figure 7 is a schematic diagram of the output photoelectric sensor at sampling point y in Figure 5;

[0038] Figure 8 is a schematic diagram of the optical eye diagram of sampling point z in Figure 5;

[0039] Figure 9 shows a schematic diagram of the circuit symbol for an N-type transistor;

[0040] Figure 10 shows a schematic diagram of the circuit symbol for a P-type transistor;

[0041] Figure 11 shows a schematic diagram of the circuit symbol for an NMOS transistor;

[0042] Figure 12 shows a schematic diagram of the circuit symbol for a PMOS transistor;

[0043] Figures 13 and 14 are circuit diagrams of a linear laser driving circuit provided in an embodiment of the present invention;

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

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

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

[0047] Figures 18 and 19 are circuit diagrams of another linear laser driving circuit provided in an embodiment of the present invention;

[0048] Figure 20 is a circuit diagram of a linear laser driving circuit provided in another embodiment of the present invention;

[0049] Figure 21 is a circuit diagram of a linear laser driving circuit provided in another embodiment of the present invention;

[0050] Figures 22 to 30 are eye diagrams of the sampling point Vout of the linear laser driving circuit provided in the embodiments of the present invention under different configurations.

[0051] In the figure, 10-laser driver; 20-laser; 110-primary linear amplifier; 120-linear branch; 121-linear transconductance path; 130-nonlinear branch; 131-current controller; 140-laser. Detailed Implementation

[0052] The linear laser driving circuit proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0053] Figure 5 is a schematic diagram of the linear laser driving circuit provided in an embodiment of the present invention. Figure 13 is a circuit diagram of a linear laser driving circuit provided in an embodiment of the present invention. Referring to Figure 5 and in conjunction with Figure 13, the linear laser driving circuit includes a primary linear amplifier 110, a linear branch 120, a nonlinear branch 130, and a laser 140.

[0054] The primary linear amplifier 110 amplifies the input differential voltage signal and outputs the amplified differential voltage signal. The differential voltage signal output by the primary linear amplifier 110 serves as the input voltage signal for 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.

[0055] The linear branch 120 is used to receive the differential voltage signal output by the primary linear amplifier and output a linear drive 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 terminal of the nonlinear branch 130 is connected to the output terminal of the linear branch 120 so that the compensation signal and the drive signal are superimposed 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-twisted branch. In other words, the nonlinear branch can pre-twist the output electrical signal before it enters the laser. In this way, the nonlinear effect of the laser itself can be compensated, the linearity of the output optical signal of the laser can be enhanced, and the performance of the optical eye diagram can be optimized. That is, by pre-distorting the eye diagram of the electrical signal (voltage or current) output by the linear laser driving circuit, and then after being distorted by the nonlinearity of the laser, a straight eye diagram and better performance are generated, so that the eye diagram has a lower TDECQ value (Transmitter and Dispersion Eye Closure Quaternary).

[0056] 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 .

[0057] The output signals of the linear signal branch and the nonlinear signal branch are superimposed (i.e., the driving signal and the compensation signal are superimposed) before being output, and then the laser is driven to generate an optical signal.

[0058] The mechanism of B(x) is to cancel the nonlinear term in the laser C(y), thereby giving the final output optical signal good linearity and a straight eye diagram. The expression for the output optical signal z of the laser is as follows: z = C(y) = c1y + c2y 2 +c3y 3 +…cn 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

[0059] In the above derivation, the fourth-order and higher nonlinear coefficients were ignored because, in practice, the values ​​of these higher-order terms are small and have little impact on the overall performance. To ensure good linearity of the final output, i.e., z≈c1(α+β1)x, the following condition must be met: c1β2+c2(α+β1). 2 ≈0 c1β3+2c2(α+β1)β2+c3(α+β1) 3 ≈0

[0060] Where 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 coefficients; α represents the parameters of specific devices in the linear branch 120, such as the relevant electrical parameters (transconductance and resistance, etc.) of the transistors in the linear branch 120; β1, β2, β3….β n All of these represent parameters of specific devices in the nonlinear branch 130, such as the relevant electrical parameters (transconductance and resistance, etc.) of the transistors in the nonlinear branch 130, where n≥3.

[0061] 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 made to hold by adjusting the parameters β1, β2, β3 of the nonlinear branch 130.

[0062] Figure 6 is a schematic diagram of the input electro-eye diagram at sampling point x in Figure 5; Figure 7 is a schematic diagram of the output electro-eye diagram at sampling point y in Figure 5; Figure 8 is a schematic diagram of the optical eye diagram at sampling point z in Figure 5. Combining Figures 6 to 8, it can be seen that at sampling point x, i.e., the linearity of the input differential voltage signal is good, and its input electro-eye diagram is also very linear, meaning that the three eyes in the input electro-eye diagram are not skewed and their heights are consistent. At sampling point y, the output electrical signal is 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 pre-distort the eye diagram of the output electrical signal, thereby compensating for the nonlinearity of the laser itself and thus offsetting the influence of the nonlinear distortion of the laser. Therefore, at sampling point z, i.e., the optical signal output by the linear laser driving circuit, the optical eye diagram is corrected. In other words, the linear laser driving circuit provided in this embodiment can correct the optical eye diagram, thereby improving the signal-to-noise ratio (SNR) and reducing the bit error rate (BER) at the sampling point.

[0063] It should be noted that the transistors involved in the following embodiments of the present invention can be bipolar transistors (also known as bipolar junction transistors) or field-effect transistors (such as metal-oxide-semiconductor field-effect transistors, MOSFETs), etc. This embodiment does not limit the type of transistor. Transistors can be divided into N-type transistors and P-type transistors. For example, Figures 8 and 9 are schematic diagrams of circuit symbols for N-type transistors (NPN) and P-type transistors (PNP), respectively; Figures 10 and 11 are schematic diagrams of circuit symbols for N-type MOSFETs (NMOS) and P-type MOSFETs (PMOS), respectively. N-type transistors can be N-type transistors (NPN) or N-type MOSFETs (NMOS), and P-type transistors can be P-type transistors (PNP) or P-type MOSFETs (PMOS). The nonlinearity of these transistors also varies with their bias state. For example, a larger bias current results in weaker nonlinearity, while a smaller bias current results in stronger nonlinearity.

[0064] For ease of description, in the embodiments, when the transistor is a bipolar junction transistor (B), the first terminal represents the base (B), the second terminal represents the collector (C), and the third terminal represents the emitter (E); when the transistor is a field-effect transistor (FET), the first terminal represents the gate (G), the second terminal represents the drain (D), and the third terminal represents the source (S). The accompanying drawings in the following embodiments of this application illustrate various circuits using a bipolar junction transistor as an example. Here, "transistor" refers to all transistors in the linear branch 120 and the nonlinear branch 130.

[0065] Figure 13 is a circuit diagram of a linear laser driving circuit provided in an embodiment of the present invention. As shown in Figure 13, after the input differential voltage signal Vin is input to the primary linear amplifier 110, the primary linear amplifier 110 amplifies the input differential voltage signal and outputs a differential voltage signal. The differential voltage signal output by the primary linear amplifier 110 includes a positive voltage signal +0.5*p*Vin and a negative voltage signal -0.5*p*Vin, where p is the gain coefficient of the primary linear amplifier. 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.

[0066] The linear branch 120 includes a first transistor Q1 and an adjustable first resistor R1, meaning the linear branch 120 is an emitter follower branch. Specifically, the first terminal of the first transistor Q1 is connected to the output terminal of the primary linear amplifier 110, specifically the first output terminal, to input the positive voltage signal. The third terminal of the first transistor Q1 is connected to the first terminal of the first resistor R1. The second terminal of the first resistor R1 is the output terminal of the linear branch 120 to output the drive signal, and the second terminal of the first resistor R1 is connected to the output terminal of the nonlinear branch 130.

[0067] As shown in Figure 13, when all transistors in the figure are N-type transistors, the second terminal of the first transistor Q1 is connected to the power supply voltage.

[0068] As shown in Figure 14, when all transistors in the figure are P-type transistors, the second terminal of the first transistor Q1 is grounded.

[0069] Referring again to Figure 13, the nonlinear branch 130 includes a second transistor Q2 and an adjustable second resistor R2. The first terminal of the second transistor Q2 is connected to the output terminal of the primary linear amplifier 110, specifically the second output terminal, to input the negative voltage signal. The second terminal of the second transistor Q2 is connected to the first resistor R1, and the third terminal of the second transistor Q2 is connected to the second resistor R2. The second terminal of the second transistor Q2 is the output terminal of the nonlinear branch 130 to output the compensation signal.

[0070] Optionally, as shown in Figure 13, when all transistors in the figure are N-type transistors, the second transistor Q2 is grounded through the second resistor R2.

[0071] As shown in Figure 14, when all transistors in the figure are P-type transistors, the second transistor Q2 is connected to the power supply voltage VDD through the second resistor R2.

[0072] The compensation signal output from the output terminal of the nonlinear branch 130 is superimposed on the driving signal output from the output terminal of the linear branch 120 and then transmitted to the laser, specifically as the load impedance transmitted to the laser.

[0073] The voltage relationship across the load impedance of the laser is as follows:

[0074] If gm1*R1>5, then

[0075] If R2 is adjusted to make gm2*R2>5, then

[0076] Where Vout represents the voltage across the load impedance of the laser (i.e., the voltage at node Vout in Figure 14); p*Vin 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 The value of the load impedance of the laser is represented by ; gm2 represents the transconductance of the second transistor Q2; and R2 represents the resistance of the second resistor R2.

[0077] 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 a relatively small impact. If the resistance of the second resistor R2 is adjusted so that the transconductance of the second transistor Q2 is less than or equal to the resistance, i.e., gm2*R2<<1; where gm2 is the transconductance of the second transistor Q2, and R2 is the resistance of the second resistor R2.

[0078] Furthermore, the voltage relationship across the load impedance of the laser is obtained as follows:

[0079] Based on the above relationship, it can be seen that since the second resistor R2 is coupled to the third terminal of the second transistor Q2, that is, the second resistor R2 is the degradation resistance of the third terminal of the second transistor Q2. Therefore, by adjusting the resistance value of the second resistor R2, the strength of the nonlinear branch 130 can be adjusted. The strength of the nonlinear branch 130 refers to the magnitude of the current, the amplitude of the voltage, or the signal characteristics (such as frequency and phase) generated by the nonlinear branch 130.

[0080] Figure 15 is a circuit diagram of another linear laser driving circuit provided in an embodiment of the present invention. In Figure 15, the linear branch 120 has the same structure as the linear branch 120 in the above embodiment, and will not be described again here.

[0081] As shown in Figure 15, the structure of the nonlinear branch 130 differs from that in the embodiment of Figure 13. Specifically, the nonlinear branch 130 includes a second transistor Q2, a third transistor Q3, and an adjustable second resistor R2. The first terminal 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 terminal of the third transistor Q3 is connected to a first bias voltage VCAS1. The second terminal of the third transistor Q3 is connected to the first resistor R1. The third terminal of the third transistor Q3 is connected to the second terminal of the second transistor Q2. The third terminal of the second transistor Q2 is connected to the second resistor R2. The second terminal of the third transistor Q3 is the output terminal of the nonlinear branch 130 to output the compensation signal.

[0082] Specifically, the third transistor Q3 is used to reduce the DC voltage at the first terminal of the second transistor Q2, thereby increasing the upper limit of the DC voltage at the output of the nonlinear branch 130 and thus improving the reliability of the second transistor Q2. Simultaneously, the third transistor Q3 can also effectively reduce the equivalent capacitance observed from the first terminal of the second transistor Q2, thereby optimizing the influence of the Miller effect capacitance. It should be noted that the equivalent capacitance observed from the first terminal of the second transistor Q2 includes the combined effects of the barrier capacitance of the PN junction inside the second transistor Q2, the diffusion capacitance, and any other possible parasitic capacitances. The capacitance value of the equivalent capacitance observed from the first terminal of the second transistor Q2 varies with the operating state of the second transistor Q2 (e.g., bias voltage or current) and the configuration of the external circuitry.

[0083] Referring to Figure 16, based on the nonlinear branch 130 shown in Figure 15, the nonlinear branch 130 may further include a fourth transistor Q4, which is coupled between the power supply voltage VDD and the third transistor Q3. The third terminal of the fourth transistor Q4 is connected to the third terminal of the third transistor Q3 and the second terminal of the second transistor Q2.

[0084] As shown in Figure 16, when all transistors are N-type transistors, the second electrode of the fourth transistor Q4 is connected to the power supply voltage VDD. Those skilled in the art should understand that when all transistors in Figure 16 are replaced with P-type transistors, the second electrode of the fourth transistor Q4 is grounded (or a low-voltage source to ensure safe operating range).

[0085] Furthermore, the first terminal of the third transistor Q3 is connected to a first bias voltage VCAS1, and the first terminal of the fourth transistor Q4 is connected to a second bias voltage VCAS2. By adjusting the voltage values ​​of the first bias voltage VCAS1 and the second bias voltage VCAS2, the current distribution ratio between the third transistor and the fourth transistor Q4 can be changed, thereby altering the gain of the nonlinear branch 130. Moreover, the combination of the third transistor Q3 and the fourth transistor Q4 adds additional degrees of adjustment freedom.

[0086] As shown in Figure 17, based on the nonlinear branch shown in Figure 16, the nonlinear branch may further include a fifth transistor Q5 and a fifth current source I5. The fifth transistor Q5 is coupled between the first terminal of the second transistor Q2 and the second output terminal of the primary linear amplifier 110. The first terminal of the fifth transistor Q5 is connected to the second output terminal of the primary linear amplifier 110, the third terminal of the fifth transistor Q5 is connected to the first terminal of the second transistor Q2, the first terminal of the fifth current source I5 is connected to the third terminal of the fifth transistor Q5, and the second terminal of the fifth transistor Q5 is connected to the power supply voltage.

[0087] In this embodiment, all transistors are N-type transistors, and the second terminal of the fifth current source I5 is grounded. Those skilled in the art should understand that when all transistors in Figure 17 are replaced with P-type transistors, the second terminal of the fifth current source I5 is connected to the power supply voltage.

[0088] In this embodiment, the fifth transistor Q5 and the fifth current source I5 constitute an emitter follower to achieve DC-DC level conversion, thereby providing a more suitable DC level to the second transistor Q2. This ensures a stable supply of the required DC level to the second transistor Q2, thus optimizing the overall performance of the nonlinear branch. Furthermore, by configuring the fifth transistor Q5 and the fifth current source I5, the response speed to high-speed signals in the nonlinear branch 130 is enhanced, and the driving capability of high-speed signals in the nonlinear branch 130 is improved, enabling the nonlinear branch to exhibit more stable and efficient performance when processing high-frequency or rapidly changing signals.

[0089] As shown in Figure 18, based on the nonlinear branch 130 shown in Figure 16, the nonlinear branch 130 may further include a DC blocking capacitor CB and an adjustable bias resistor RB. The DC blocking capacitor CB is coupled between the first terminal of the second transistor Q2 and the second output terminal of the primary linear amplifier 110, and the bias resistor RB is coupled between the first terminal of the second transistor Q2 and the adjustable bias voltage VB.

[0090] The DC blocking capacitor CB and the bias resistor RB are used to isolate the DC level of the first terminal of the second transistor Q2 from the preceding stage. This allows for free control of the DC voltage at the first terminal of the second transistor Q2 by adjusting the adjustable bias voltage, which is beneficial for optimizing the stability and flexibility of the nonlinear branch 130. Furthermore, the DC blocking capacitor CB and the bias resistor RB can also determine the high-pass corner frequency for high-speed signal transmission. By adjusting the resistance value of the bias resistor RB, the signal energy transmission at different frequencies can be adjusted, thereby optimizing high-speed performance. Additionally, adjusting the adjustable bias voltage VB can adjust the DC current of the second transistor Q2, thereby adjusting the nonlinear characteristics in the transconductance (gm2) of the second transistor Q2.

[0091] As shown in Figure 18, when all the transistors in the nonlinear branch 130 are N-type transistors, the second terminal of the fourth transistor Q4 is connected to the power supply voltage, the second terminal of the first transistor Q1 is connected to the power supply voltage VDD, and one end of the second resistor R2 is grounded.

[0092] As shown in Figure 19, when all transistors in the nonlinear branch 130 are P-type transistors, the second terminal of the fourth transistor Q4 is grounded (or a low voltage source is used to ensure safe operating range), the second terminal of the first transistor Q1 is grounded, and the third terminal of the second transistor Q2 is connected to the power supply voltage VDD through the second resistor R2.

[0093] The present invention also provides another linear laser driving circuit. As shown in FIG20, the linear laser driving circuit includes a primary linear amplifier 110, a linear branch 120, and a nonlinear branch 130.

[0094] As shown in Figure 20, 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 output it, thereby outputting a positive voltage signal +0.5*p*Vin and a negative voltage signal -0.5*p*Vin.

[0095] As shown in Figure 20, 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 a current signal before outputting it. 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.

[0096] The third resistor R3 is coupled to the output terminal of the linear transconductance path 121, serving as the load resistor of the linear transconductance path 121 to convert the current signal into a voltage signal, which is then used as the driving signal. Furthermore, the third resistor R3 is also coupled to the output terminal of the nonlinear branch 130, serving as the load resistor for both the linear transconductance path 121 and the nonlinear branch 130. This not only converts the current signal output from the linear transconductance path 121 into a voltage signal but also achieves output impedance matching.

[0097] As shown in Figure 20, the nonlinear branch 130 includes a second transistor Q2, a fourth transistor Q4, a fifth transistor Q5, an adjustable capacitor C1, a DC blocking capacitor CB, a first resistor R1, and a bias resistor RB.

[0098] The first terminal of the second transistor Q2 is connected to the first output terminal of the primary linear amplifier 110 through the DC blocking capacitor CB.

[0099] The second terminal of the second transistor Q2 is connected to the third terminal of the fourth transistor Q4, the second terminal of the fourth transistor Q4 is connected to the output terminal of the linear transconductance path 121, and the second terminal of the fourth transistor Q4 is the output terminal of the nonlinear branch 130 to output the compensation signal.

[0100] The third terminal of the fifth transistor Q5 is connected to the third terminal of the fourth transistor Q4 and the second terminal of the second transistor Q2. The first terminal of the fifth transistor Q5 is coupled to the fifth bias voltage VCAS5, and the first terminal of the fourth transistor Q4 is coupled to the fourth bias voltage VCAS4. Thus, by adjusting the voltage values ​​of the fourth bias voltage VCAS5 and the fifth bias voltage VCAS5, the proportion of current flowing to the third transistor Q3 in the nonlinear branch 130 can be adjusted, thereby changing the overall gain of the nonlinear branch 130.

[0101] In this embodiment, all transistors are N-type transistors, and the second terminal of the fifth transistor is connected to the power supply voltage VDD. Those skilled in the art should understand that when all transistors in Figure 20 are replaced with P-type transistors, the second terminal of the fifth transistor is grounded (or a low-voltage source is used to ensure safe operating range).

[0102] The adjustable capacitor C1 and the first resistor R1 are both coupled to the third terminal of the second transistor Q2. Decreasing the resistance of the first resistor R1 enhances the nonlinear characteristics of the nonlinear branch 130. Increasing the capacitance of the adjustable capacitor C1 enhances the nonlinearity of the high-frequency signal components.

[0103] The bias resistor RB is coupled between the first terminal of the second transistor Q2 and the adjustable bias voltage VB, and is also connected to the DC blocking capacitor CB. That is, the nonlinear branch 130 uses AC coupling composed of the DC blocking capacitor CB and the bias resistor RB for single-ended input. Furthermore, the first terminal of the second transistor Q2 is coupled to the adjustable bias voltage VB through the bias resistor RB. Thus, the DC blocking capacitor CB and the bias resistor RB can isolate the DC voltage of the first terminal of the second transistor Q2 from the preceding circuit. By adjusting the adjustable bias voltage VB, the DC voltage and DC current of the first terminal of the second transistor Q2 can be freely adjusted, thereby adjusting the nonlinear characteristics in the transconductance of the second transistor Q2. In other words, the pre-twisting intensity can be freely adjusted, thus adapting to different types of lasers (different types of lasers have different nonlinearities) and different operating temperatures (the nonlinearity will also change when the laser temperature changes).

[0104] In addition, the DC blocking capacitor CB and the bias resistor RB can determine the high-pass corner frequency of 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 at different frequencies and thus optimizing high-speed performance.

[0105] In a further embodiment, as shown in Figure 20, the nonlinear branch 130 may also include a third current source I3, which is an adjustable current source. The third current source I3 is coupled to the output terminal of the nonlinear branch 130 and the output terminal of the linear branch 120. The third current source I3 is used to compensate for the DC current output by the linear branch 120 and the nonlinear branch 130, so as to compensate for the DC current input to the laser 140.

[0106] The present invention also provides another linear laser driving circuit. As shown in FIG21, the linear laser driving circuit includes a primary linear amplifier 110, a nonlinear branch 130, and a linear branch 120.

[0107] As shown in Figure 21, 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 output it, thereby outputting a positive voltage signal +0.5*p*Vin and a negative voltage signal -0.5*p*Vin.

[0108] It should be noted that the linear branch shown in Figure 21 has the same structure as the linear branch described in Figure 20, and will not be described again here. However, the nonlinear branch shown in Figure 21 has a different structure than the nonlinear branch described in Figure 20.

[0109] As shown in Figure 21, 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 terminal of the first transistor is connected to the second output terminal of the primary linear amplifier, and the second terminal of the first transistor Q1 is connected to the third terminal of the third transistor Q3.

[0110] The second terminal of the fourth transistor Q4 is connected to the output terminal of the linear transconductance path 121, and the second terminal of the fourth transistor Q4 outputs the compensation signal. The third terminal of the fourth transistor Q4 is connected to the second terminal of the second transistor Q2, and the first terminal of the second transistor Q2 is connected to the first output terminal of the primary linear amplifier.

[0111] The second terminal of the fifth transistor Q5 is connected to the power supply voltage or ground, and the third terminal of the fifth transistor Q5 is connected to the third terminal of the fourth transistor Q4 and the second terminal of the second transistor Q2. The first terminal of the fourth transistor Q4 is coupled to the fourth bias voltage VCAS4, and the first terminal 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 branch current flowing to the third transistor Q3 can be adjusted, thereby changing the overall gain of the nonlinear branch 130.

[0112] In this embodiment, all transistors are N-type transistors. The second and first terminals of the third transistor Q3 and the second terminal of the fifth transistor Q5 are all connected to the power supply voltage VDD, and the second terminal of the fourth transistor Q4 is connected to the power supply voltage VDD through the third resistor R3.

[0113] Those skilled in the art should understand that when all the transistors in Figure 21 are replaced with P-type transistors, the second and first terminals of the third transistor Q3 and the second terminal of the fifth transistor Q5 are grounded (or a low voltage source to ensure safe operating range), and the second terminal of the fourth transistor Q4 is grounded through the third resistor R3.

[0114] 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 terminal of the second transistor Q2 and the third terminal of the first transistor Q1.

[0115] The first current source is coupled to the third terminal of the first transistor Q1, and the second current source is coupled to the third terminal of the second transistor Q2.

[0116] 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 relationship between the current values ​​of the first current source I1 and the second current source I2 is as follows: I1=(1+γ)*I S I2=(1-γ)*I S ;

[0117] Where I1 represents the current value of the first current source; I2 represents the current value of the second current source; I S It represents a fixed current value; γ represents the control coefficient, and -1 < γ < 1;

[0118] Based on the above relationships, it can be seen that when the control coefficient γ = 0, the smaller (or weaker) the nonlinearity of the nonlinear branch 130, and the closer |γ| is to 1, the stronger the nonlinearity of the nonlinear branch 130. Therefore, by controlling 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 nonlinearity intensity of the nonlinear branch 130 can be adjusted.

[0119] In the nonlinear branch 130 of this embodiment, a smaller bias current design is employed to enhance its nonlinear characteristics. In practical applications, the additional current consumed by the nonlinear branch 130 accounts for approximately 5% to 10% of the total current, thus not significantly increasing the overall power consumption of the system. Conversely, when the nonlinear branch 130 is enabled, the DSP in the front-end of the system can reduce the intensity of its DPD (digital pre-distortion), thereby reducing the overall power consumption of the system and consequently lowering costs.

[0120] In a further embodiment, the linear laser driving circuit also includes a capacitor C, which is a DC blocking capacitor, and the capacitor is coupled to the output terminals of the linear branch 120 and the nonlinear branch 130.

[0121] In this embodiment, the output electrical signal of the superposition of nonlinear branch 130 and linear branch 120 is output to laser 140. Laser 140 is a linear laser, which includes a laser diode and a load impedance. The laser diode is used to convert electrical energy into laser light. To better illustrate the inventive point of this invention, the description and illustration of the laser diode are omitted. The laser can be a VCSEL (Vertical-Cavity Surface-Emitting Laser), DFB (Distributed Feedback Laser), EML (Electro-Absorption Modulated Laser), or MZM (Mach-Zehnder Modulator).

[0122] Figures 22 to 30 are eye diagrams of the laser output terminal under different configurations of the linear laser driving circuit provided in the embodiments of the present invention. In Figures 22 to 30, the horizontal axis represents time, and the vertical axis represents the voltage at the sampling point Vout. Figure 22 is an eye diagram of the sampling point Vout in the linear laser driving circuit based on Figure 13. Figures 23 to 26 are eye diagrams of the sampling point Vout of the nonlinear branch in the linear laser driving circuit shown in Figure 13 under different configurations. As can be seen from Figures 23 to 26, adjusting different configurations in the nonlinear branch can result in different eye diagram effects at the sampling point Vout, that is, different pre-distortions can be generated in the nonlinear branch. Figures 27 to 30 are all schematic diagrams of the eye diagram of the sampling point Vout in the linear laser driving circuit based on Figure 21. Among them, the eye diagram of Figure 27 is a schematic diagram of the eye diagram when the nonlinear branch is closed, and Figures 28 to 30 are the eye diagrams of the sampling point Vout when the nonlinear branch is open. Figures 28 to 30 are eye diagrams under different distortion configurations. Comparing Figures 27 to 30, it can be seen that when the nonlinear branch is open, 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.

[0123] In summary, the linear laser driving circuit provided by this invention includes a primary linear amplifier, a linear branch, and a nonlinear branch. The nonlinear branch receives the negative voltage signal output from the primary linear amplifier and outputs a nonlinear compensation signal to compensate for the nonlinear effect of the laser. The output terminal of the nonlinear branch is connected to the output terminal of the linear branch, so that the compensation signal output by the nonlinear branch is superimposed with the driving signal output by the linear branch to form an output electrical signal. This compensates for the nonlinear effect of the laser itself, enhances the linearity of the output optical signal, and optimizes the performance of the optical eye diagram.

[0124] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A linear laser driving circuit, characterized in that, include: A primary linear amplifier is used to amplify an input differential voltage signal and output an amplified differential voltage signal, wherein the differential voltage signal includes a positive voltage signal and a negative voltage signal; A linear branch is used to receive the differential voltage signal output by the primary linear amplifier and output a linear drive 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 terminal of the nonlinear branch is connected to the output terminal of the linear branch so that the compensation signal is superimposed with the driving 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 as described in claim 1, characterized in that, The linear branch includes: A first transistor and an adjustable first resistor, wherein the first terminal of the first transistor is connected to the first output terminal of the primary linear amplifier to input the positive voltage signal, the second terminal of the first transistor is connected to the power supply voltage or ground, the third terminal of the first transistor is connected to one end of the first resistor, the first end of the first resistor is the output terminal of the linear branch to output the drive signal, and the second end of the first resistor is connected to the output terminal of the nonlinear branch.

3. The linear laser driving circuit as described in claim 2, characterized in that, The nonlinear branch includes a second transistor and an adjustable second resistor. The first terminal of the second transistor is connected to the second output terminal of the primary linear amplifier to input the negative voltage signal. The second terminal of the second transistor is connected to the first resistor. The third terminal of the second transistor is connected to the first terminal of the second resistor. The second terminal of the second resistor is connected to the power supply voltage or ground. The second terminal of the second transistor is the output terminal of the nonlinear branch to output the compensation signal.

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

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

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

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

8. The linear laser driving circuit as described in claim 1, characterized in that, The linear branch includes: A linear transconductance path is provided, which 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 a current signal and then output them. A third resistor is coupled to the output of the linear transconductance path to convert the current signal into a voltage signal, which serves as the driving signal.

9. The linear laser driving circuit as described in 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 terminal of the first transistor is connected to the second output terminal of the primary linear amplifier, and the second terminal of the first transistor is connected to the third terminal of the third transistor. Both the second and first terminals of the third transistor are connected to the power supply voltage or ground. The first terminal of the fourth transistor is coupled to the fourth bias voltage, the second terminal of the fourth transistor is connected to the output terminal of the linear transconductance path, and the second terminal of the fourth transistor outputs the compensation signal. The third terminal of the fourth transistor is connected to the second terminal of the second transistor, and the first terminal of the second transistor is connected to the first output terminal of the primary linear amplifier. The first terminal of the fifth transistor is coupled to the fifth bias voltage, the second terminal of the fifth transistor is connected to the power supply voltage or ground, and the third terminal of the fifth transistor is connected to the third terminal of the fourth transistor and the second terminal of the second transistor. The first resistor and the adjustable capacitor are connected in parallel, and both the first resistor and the adjustable capacitor are coupled between the third terminal of the second transistor and the third terminal of the first transistor. The first terminal of the first current source is coupled to the third terminal of the first transistor and the second terminal of the first current source is connected to the power supply voltage or ground. The first terminal of the second current source is coupled to the third terminal of the second transistor and the second terminal of the second current source is connected to the power supply voltage or ground. 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 as described in 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 terminal of the second transistor is connected to the first output terminal of the primary linear amplifier through the DC blocking capacitor, and the second terminal of the second transistor is connected to the third terminal of the fourth transistor; The first terminal of the fourth transistor is coupled to the fourth bias voltage, the second terminal of the fourth transistor is connected to the output terminal of the linear transconductance path, and the second terminal of the fourth transistor is the output terminal of the nonlinear branch to output the compensation signal. The first terminal of the fifth transistor is coupled to the fifth bias voltage, the second terminal of the fifth transistor is connected to the power supply voltage or ground, and the third terminal of the fifth transistor is connected to the third terminal of the fourth transistor and the second terminal of the second transistor. The adjustable capacitor and the first resistor are both coupled between the third terminal of the second transistor and ground; The bias resistor is coupled between the first terminal of the second transistor and the adjustable bias voltage, and the bias resistor is connected to one end of the DC blocking capacitor.

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