A current-to-voltage conversion circuit, a transmitter and a signal transmission system

Abstract

The application provides a voltage-current conversion circuit, which comprises a low-frequency voltage-current conversion branch, a high-frequency signal compensation branch and a high-frequency voltage-current conversion branch. The input ends of the high-frequency signal compensation branch are connected with an input signal and the low-frequency voltage-current conversion branch respectively. The high-frequency voltage-current conversion branch is connected in parallel with the low-frequency voltage-current conversion branch between an electro-optical conversion module and a negative power supply. The voltage-current conversion circuit provided by the application can make the total current flowing through the electro-optical conversion module reach a higher frequency range through the cooperation of the high-frequency signal compensation branch and the high-frequency voltage-current conversion branch, and does not need to separately filter the input signal, thereby reducing the cost and ensuring the accuracy of signal transmission through the reduction of branch links. The application also provides a transmitter and a signal transmission system using the voltage-current conversion circuit.

Description

[Technical Field]

[0001] This invention relates to the field of signal transmission technology, and in particular to a voltage-to-current conversion circuit, a transmitter, and a signal transmission system. [Background Technology]

[0002] With the development of signal transmission technology, the method of converting electrical signals into optical signals for transmission is becoming increasingly common. A typical signal transmission system consists of three parts: a transmitter, optical fiber, and a signal receiver. The transmitter receives and converts the signal; if errors exist, the converted signal received by the receiver will be distorted. The voltage-to-current conversion circuit within the transmitter is the main circuit that converts the input signal into an optical signal. Together with the electro-optical conversion module, it achieves the conversion between electrical and optical signals.

[0003] Modern laser diodes or light-emitting diodes (LEDs) (hereinafter, only laser diodes will be described) are electro-optical conversion devices in which luminous intensity and driving current have a linear relationship. High-frequency modulation of the driving current of a laser diode yields a modulated optical signal, which is then converted into an electrical signal by a photoelectric receiving circuit. This enables isolated transmission of electrical signals, such as in optocoupler applications. This optical isolation technology has wide applications in the field of electronics.

[0004] Because a laser diode is a unidirectional conductive device, a static operating current Is must be set for it in order to transmit an input voltage signal with both positive and negative values. This allows the laser diode's operating current ILD to vary within a linear range around the static operating current Is when a voltage signal Vin is input, resulting in a linear change in the laser diode's output optical power Po. In existing technologies, voltage-to-current conversion circuits cannot simultaneously address the issues of high-speed modulation and temperature drift, making them unsuitable for high-precision applications.

[0005] Prior art, application number 202311550411.3, discloses a voltage-to-current conversion circuit, including a signal acquisition branch, a first voltage-to-current conversion branch, and a second voltage-to-current conversion branch. The first voltage-to-current conversion branch includes a first power transistor. On one hand, the signal acquisition branch acquires a first high-frequency component from the input signal and inputs it to the first voltage-to-current conversion branch. The first voltage-to-current conversion branch generates a first current based on the first high-frequency component, thereby enabling high-speed modulation. On the other hand, the signal acquisition branch also acquires a first voltage at the emitter of the first power transistor and outputs a first signal to the second voltage-to-current conversion branch based on the first voltage. The second voltage-to-current conversion branch then generates a second current based on the first signal. Simultaneously, by connecting the second voltage-to-current conversion branch in parallel with the first voltage-to-current conversion branch to sum the first current and the second current to eliminate the first voltage, temperature drift can be ensured.

[0006] However, the existing technology requires adding a signal acquisition branch to filter the input signal. The filtered high-frequency component is then input to the first voltage-current conversion branch, which increases the cost of circuit design. Furthermore, the addition of a branch during signal transmission increases the risk of signal transmission errors. [Summary of the Invention]

[0007] This invention provides a voltage-to-current conversion circuit, transmitter, and signal transmission system to solve the above-mentioned problems, thereby reducing design costs and improving signal transmission accuracy.

[0008] This invention provides a voltage-to-current conversion circuit, including a low-frequency voltage-to-current conversion branch, a high-frequency signal compensation branch, and a high-frequency voltage-to-current conversion branch. The low-frequency voltage-to-current conversion branch includes a first power transistor and a first operational amplifier. The non-inverting input terminal of the first operational amplifier is connected to an input signal, the inverting input terminal of the first operational amplifier is connected to the emitter of the first power transistor, and the output terminal of the first operational amplifier is connected to the base of the first power transistor. The input terminals of the high-frequency signal compensation branch are respectively connected to the non-inverting and inverting input terminals of the first operational amplifier. The high-frequency voltage-to-current conversion branch is connected in parallel with the low-frequency voltage-to-current conversion branch, and the input terminal of the high-frequency voltage-to-current conversion branch is connected to the output terminal of the high-frequency signal compensation branch.

[0009] Meanwhile, the present invention provides a transmitter, which includes an electro-optic conversion module and a voltage-to-current conversion circuit. The electro-optic conversion module is a laser diode or a light-emitting diode. The voltage-to-current conversion circuit includes a low-frequency voltage-to-current conversion branch, a high-frequency signal compensation branch, and a high-frequency voltage-to-current conversion branch. The low-frequency voltage-to-current conversion branch includes a first power transistor and a first operational amplifier. The non-inverting input terminal of the first operational amplifier is connected to the input signal, the inverting input terminal of the first operational amplifier is connected to the emitter of the first power transistor, and the output terminal of the first operational amplifier is connected to the base of the first power transistor. The input terminals of the high-frequency signal compensation branch are respectively connected to the non-inverting and inverting input terminals of the first operational amplifier. The high-frequency voltage-to-current conversion branch is connected in parallel with the low-frequency voltage-to-current conversion branch, and the input terminal of the high-frequency voltage-to-current conversion branch is connected to the output terminal of the high-frequency signal compensation branch.

[0010] The present invention also provides a signal transmission system, the signal transmission system comprising a signal receiver, an optical fiber, and a transmitter, the transmitter comprising an electro-optic conversion module and a voltage-to-current conversion circuit, the electro-optic conversion module being a laser diode or a light-emitting diode; the voltage-to-current conversion circuit comprising a low-frequency voltage-to-current conversion branch, a high-frequency signal compensation branch, and a high-frequency voltage-to-current conversion branch, the low-frequency voltage-to-current conversion branch comprising a first power transistor and a first operational amplifier; the non-inverting input terminal of the first operational amplifier is connected to the input signal, the inverting input terminal of the first operational amplifier is connected to the emitter of the first power transistor, and the output terminal of the first operational amplifier is connected to the base of the first power transistor; the input terminals of the high-frequency signal compensation branch are respectively connected to the non-inverting and inverting input terminals of the first operational amplifier, the high-frequency voltage-to-current conversion branch is connected in parallel with the low-frequency voltage-to-current conversion branch, and the input terminal of the high-frequency voltage-to-current conversion branch is connected to the output terminal of the high-frequency signal compensation branch.

[0011] Compared with the prior art, the present invention provides a voltage-to-current conversion circuit, a transmitter, and a signal transmission system. The voltage-to-current conversion circuit includes a low-frequency voltage-to-current conversion branch, a high-frequency signal compensation branch, and a high-frequency voltage-to-current conversion branch. The low-frequency voltage-to-current conversion branch, by incorporating a first power transistor and a first operational amplifier, forms a low-frequency signal channel based on the characteristics of the first operational amplifier, converting the low-frequency signal entering the low-frequency voltage-to-current conversion branch into a low-frequency drive current. Through the cooperation of the high-frequency signal compensation branch and the high-frequency voltage-to-current conversion branch, the high-frequency signal entering the high-frequency voltage-to-current conversion branch is converted into a high-frequency drive current. High-frequency drive current; the two currents are superimposed, and the high-frequency drive current of the high-frequency voltage-to-current conversion branch exactly compensates for the deficiency of the low-frequency drive current of the low-frequency voltage-to-current conversion branch. After compensation, the total current flowing through the electro-optical conversion module can reach a very high frequency range, such as DC-2GHz. The low-frequency voltage-to-current conversion branch is a closed-loop voltage-to-current conversion channel with high-precision voltage-to-current conversion characteristics, ensuring that there is no temperature drift at the DC static operating point. On this basis, the voltage-to-current conversion circuit does not need to perform separate filtering processing on the input signal, which reduces the cost of circuit design, and reduces the number of filtering branches during signal transmission, thereby increasing the accuracy of signal transmission. [Attached Image Description]

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0013] Figure 1This is a schematic diagram of the signal transmission system structure provided in this application;

[0014] Figure 2 This is a schematic diagram of the voltage-to-current conversion circuit provided in Embodiment 1 of this application;

[0015] Figure 3 yes Figure 2 A schematic diagram of each signal in the structure shown;

[0016] Figure 4 This is a schematic diagram of the voltage-to-current conversion circuit provided in Embodiment 2 of this application; and

[0017] Figure 5 This is a schematic diagram of the voltage-current conversion circuit provided in Embodiment 3 of this application.

Detailed Implementation Methods

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please refer to the following at the same time. Figure 1 and Figure 2 ,in, Figure 1 This is a schematic diagram of the signal transmission system structure provided in this application. Figure 2 This is a schematic diagram of the voltage-to-current conversion circuit provided in Embodiment 1 of this application. The signal transmission system 100 provided by this invention includes a transmitter 10, an optical fiber 30, and a signal receiver 50. The transmitter 10 includes a voltage-to-current conversion circuit 11, an electro-optical conversion module 13, a positive power supply V+, and a negative power supply V-. The electro-optical conversion module 13 is a laser diode or a light-emitting diode, one end of which is connected to the positive power supply V+. The voltage-to-current conversion circuit 11 is disposed between the electro-optical conversion module 13 and the negative power supply V-. Of course, in another embodiment, the negative power supply V- can also be grounded, depending on the specific situation, and is not limited here. The optical fiber 30 is disposed between the transmitter 10 and the signal receiver 50. The voltage-to-current conversion circuit 11 and the electro-optical conversion module 13 in the transmitter 10 convert the input signal Vin into an optical signal, which is transmitted to the signal receiver 50 via the optical fiber 30. The signal receiver 50 converts the optical signal into an electrical signal, thereby realizing signal transmission. The voltage-to-current conversion circuit 11 and the electro-optical conversion module 13 are located between the positive power supply V+ and the negative power supply V-. The voltage-to-current conversion circuit 11 converts the input signal Vin into a precise DC current signal to control the electro-optical conversion module 13.

[0020] Therefore, the signal transmission system 100 has a simple and practical structure. During the signal transmission process, the voltage-to-current conversion circuit 11 can accurately transmit the input signal Vin through the optical fiber 30 to the signal receiver 50, and then the signal receiver 50 performs photoelectric conversion. Without the need for additional control devices or signal feedback devices, efficient and accurate signal transmission can be achieved.

[0021] like Figure 2 As shown, the voltage-to-current conversion circuit 11 includes a low-frequency voltage-to-current conversion branch 111, a high-frequency signal compensation branch 113, and a high-frequency voltage-to-current conversion branch 115. The low-frequency voltage-to-current conversion branch 111 includes a first power transistor Q1, a first operational amplifier A1, and a first resistor R1. The non-inverting input terminal of the first operational amplifier A1 is connected to the input signal Vin, the inverting input terminal of the first operational amplifier A1 is connected to the emitter of the first power transistor Q1, and the output terminal of the first operational amplifier A1 is connected to the first power transistor Q1. The base of transistor Q1 is connected, and the first resistor R1 is located between the emitter of the first power transistor Q1 and the negative power supply V-. The input terminal of the high-frequency signal compensation branch 113 is connected to the input signal Vin and the low-frequency voltage-current conversion branch 111 respectively. The high-frequency voltage-current conversion branch 115 is connected in parallel with the low-frequency voltage-current conversion branch 111 between the electro-optical conversion module 13 and the negative power supply V-. The input terminal of the high-frequency voltage-current conversion branch 115 is connected to the output terminal of the high-frequency signal compensation branch 113.

[0022] The low-frequency voltage-to-current conversion branch 111 is equipped with the first operational amplifier A1, forming a closed-loop voltage-to-current conversion channel with high-precision voltage-to-current conversion characteristics, ensuring no temperature drift at the DC static operating point. Furthermore, unlike existing technologies that filter and split the input signal Vin by setting up other branches, the low-frequency voltage-to-current conversion branch 111, based on this design, achieves low-frequency and high-frequency signal splitting through automatic switching between the effective and ineffective states of the closed loop, saving costs and reducing signal processing steps.

[0023] In this first embodiment, the high-frequency signal compensation branch 113 includes a subtractor A2. The non-inverting input of the subtractor A2 is connected to the non-inverting input of the first operational amplifier A1 and the input signal Vin. The inverting input of the subtractor A2 is connected to the inverting input of the first operational amplifier A1 and the emitter of the first power transistor Q1. The output of the subtractor A2 is connected to the input of the high-frequency voltage-to-current conversion branch 115. The subtractor A2 works in conjunction with the low-frequency voltage-to-current conversion branch 111 to output the high-frequency signal shunted by the low-frequency voltage-to-current conversion branch 111. Based on this, the high-frequency drive current generated by the high-frequency voltage-to-current conversion branch 115 precisely compensates for the insufficient low-frequency drive current of the low-frequency voltage-to-current conversion branch 111, ensuring that the total current of the electro-optical conversion module can reach a very high frequency range.

[0024] In this first embodiment, the high-frequency voltage-to-current conversion branch 115 includes a second power transistor Q2, a first capacitor C1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a temperature compensation diode D1. The first terminal of the first capacitor C1 is connected to the output terminal of the high-frequency signal compensation branch 113, and the second terminal of the first capacitor C1 is connected to the base of the second power transistor Q2. The second resistor R2 is located between the emitter of the second power transistor Q2 and the negative power supply V-. The first terminal of the third resistor R3 is connected to the positive power supply V+, and the second terminal of the third resistor R3 is connected to the base of the second power transistor Q2. The fourth resistor R4 is connected in series with the third resistor R3 between the positive power supply V+ and the negative power supply V-, and the first terminal of the fourth resistor R4 is connected to the negative power supply V-. The anode of the temperature compensation diode D1 is connected to the second terminal of the third resistor R3 and the base of the second power transistor Q2, and the cathode of the temperature compensation diode D1 is connected to the second terminal of the fourth resistor R4.

[0025] In this first embodiment, the electro-optic conversion module 13 is preferably a laser diode LD1.

[0026] The working principle of Example 1 is described below:

[0027] like Figure 2As shown, the negative power supply V- is the negative power supply of the constant current drive circuit, the positive power supply V+ is the positive power supply of the constant current drive circuit, the first voltage V1 is the output voltage of the first power transistor Q1, the second voltage V2 is the output voltage of the subtractor A2, the third voltage V3 is the DC operating point voltage of the base of the second power transistor Q2, the fourth voltage V4 is the DC voltage across the second resistor R2, the first current I1 is the current of the low-frequency voltage-current conversion branch 111, the second current I2 is the current of the high-frequency voltage-current conversion branch 115, and the total current ILD1 is the current of the laser diode LD1.

[0028] First, the input signal Vin enters the voltage-to-current conversion circuit 11 and drives the low-frequency voltage-to-current conversion branch 111. The input signal Vin is connected to the non-inverting input terminal of the first operational amplifier A1, and the inverting input terminal of the first operational amplifier A1 is connected to the first terminal of the first resistor R1. The laser diode LD1, the first power transistor Q1, the first resistor R1, and the first operational amplifier A1 constitute a closed-loop controlled low-frequency voltage-to-current conversion channel.

[0029] In closed-loop operation, the voltage at the non-inverting input of the first operational amplifier A1 is equal to the voltage at the inverting input, i.e., V1 = Vin. Therefore, the first current I1 can be calculated as I1 = (V1 - V-) / R1 = (Vin - V-) / R1. Based on the characteristics of the subtractor A2, in closed-loop operation, the first voltage V1 follows the change in the input signal Vin. The second voltage V2 corresponding to the output of the subtractor A2 is 0, meaning the input signal of the high-frequency voltage-to-current conversion branch 115 is 0, and the second current I2 is 0.

[0030] In the closed-loop failure state, the first voltage V1 cannot follow the change of the input signal Vin. The first voltage V1 is less than the input signal Vin. Then, according to the characteristics of the subtractor A2, V2 = Vin - V1. The second voltage V2 is input to the high-frequency voltage-current conversion branch 115 to form the second current I2 to compensate for the high-frequency signal lost by the low-frequency voltage-current conversion branch 111.

[0031] The low-frequency voltage-to-current conversion branch 111 is a closed-loop voltage-to-current conversion channel, responsible for the closed-loop voltage-to-current conversion from DC to low frequency. Because it is a closed loop, it has high-precision voltage-to-current conversion characteristics, and there is no temperature drift at the DC static operating point.

[0032] Secondly, in the high-frequency voltage-to-current conversion branch 115, the third resistor R3, the fourth resistor R4, and the light-emitting diode D1 form a DC-operated voltage divider circuit, forming a stable DC operating point voltage, namely the third voltage V3, at the base of the second power transistor Q2. The third voltage V3 includes the voltage of the temperature compensation diode D1, used to compensate for the temperature drift of the VBE voltage of the second power transistor Q2. Of course, to ensure that the temperature characteristics of these two transistors are completely identical, the temperature compensation diode D1 can also be replaced by the BE junction voltage of a transistor of the same type as the second power transistor Q2; this is not a limitation.

[0033] The third voltage V3 is subtracted from the VBE voltage of the second power transistor Q2 (the voltage drop between the fixed voltage BE of the transistor, which is generally around 0.7V) to obtain the DC voltage across the second resistor R2, which is the fourth voltage V4 (DC).

[0034] The formula for calculating the DC operating point current of the second current I2 output in the high-frequency voltage-to-current conversion branch 115 is I2(DC) = V4(DC) / R2 = (V3(DC) - VBE) / R2. Therefore, it can be seen that the temperature drift of the VBE voltage of the second power transistor Q2 will affect the DC operating point current of the second current I2. The PN junction voltage of the temperature compensation diode D1 in the circuit also changes with temperature, and the temperature drift pattern is the same as that of the VBE voltage of the second power transistor Q2. Thus, the temperature drift of the VBE voltage of the second power transistor Q2 will be offset by the temperature drift of the PN junction voltage of the temperature compensation diode D1. This makes the high-frequency voltage-to-current conversion branch 115 of the present invention a voltage-to-current conversion channel with a stable DC operating point.

[0035] Furthermore, the second voltage V2 is supplied to the first capacitor C1 in the high-frequency voltage-to-current conversion branch 115. Since the first capacitor C1 is AC short-circuited for high-frequency signals, and the VBE of the second power transistor Q2 is a fixed voltage drop between the transistor's BE, typically around 0.7V, this DC voltage is also short-circuited for high-frequency AC components. Therefore, V2 = V3(AC) = V4(AC). Further, the high-frequency AC component of the second current I2 in the high-frequency voltage-to-current conversion branch 115 can be calculated: I2(AC) = V2 / R2.

[0036] Preferably, R1 = R2, then I2(AC) = V2 / R1. It can be seen that the second voltage V2 of the subtractor A2 forms a compensating current in the high-frequency voltage-to-current conversion branch 115. The second current I2(AC) perfectly compensates for the insufficient high-frequency characteristics of the low-frequency voltage-to-current conversion branch 111.

[0037] Finally, based on the analysis of the low-frequency voltage-to-current conversion branch 111, it can be concluded that the total current ILD1 flowing through the laser diode LD1 consists of four parts:

[0038] The static operating current I1(DC) of the low-frequency voltage-current conversion branch 111;

[0039] The signal operating current I1(AC) of the low-frequency voltage-current conversion branch 111;

[0040] The static operating current I2 (DC) of the high-frequency voltage-current conversion branch 115;

[0041] The high-frequency voltage-current conversion branch 115 compensates for the AC high-frequency current I2(AC).

[0042] ILD1=I1+I2=I1(DC)+V1 / R1+I2(DC)+V2 / R1.

[0043] The first current I1 and the input signal Vin are linearly related. Due to the frequency characteristics of the first operational amplifier A1, the operating frequency of the low-frequency voltage-to-current conversion branch 111 generally does not exceed 50MHz. The high-frequency voltage-to-current conversion branch 115 perfectly compensates for the lack of high-frequency characteristics of the signal operating current of the low-frequency voltage-to-current conversion branch 111.

[0044] Please see Figure 3 , Figure 3 yes Figure 2 The diagram shows the signals in the structure. The different frequencies of the input signal Vin correspond to changes in the first current I1, the second voltage V2, the second current I2, and the total current ILD1.

[0045] like Figure 3 As shown, f1 is the high-frequency cutoff frequency of the closed loop. When the frequency of the input signal Vin exceeds f1, the low-frequency voltage-to-current conversion branch 111 fails to close the loop. After the closed loop fails, the first current I1 output by the low-frequency voltage-to-current conversion branch 111 and the input voltage Vin are no longer linearly related. As the frequency of the input signal Vin increases, the high-frequency component of the input signal Vin corresponds to a smaller and smaller high-frequency current of the first current I1. The second current I2 output by the high-frequency voltage-to-current conversion branch 115 effectively compensates for the loss of the high-frequency signal of the low-frequency voltage-to-current conversion branch 111, and the total current ILD1 signal remains stable.

[0046] The technical solution of connecting the high-frequency voltage-to-current conversion branch 115 in parallel with the low-frequency voltage-to-current conversion branch 111 provided in this embodiment can achieve a very high modulation frequency without temperature drift at the DC operating point. If the first power transistor Q1 is a high-speed transistor, the modulation frequency of the voltage-to-current conversion circuit 11 can reach about 2 GHz.

[0047] Please see Figure 4 , Figure 4 This is a schematic diagram of the voltage-to-current conversion circuit provided in Embodiment 2 of this application. The voltage-to-current conversion circuit 11 includes a low-frequency voltage-to-current conversion branch 111, a high-frequency signal compensation branch 113, and a high-frequency voltage-to-current conversion branch 115. For example... Figure 4 As shown, the negative power supply V- is the negative power supply of the constant current drive circuit, the positive power supply V+ is the positive power supply of the constant current drive circuit, the first voltage V1 is the output voltage of the first power transistor Q1, the second voltage V2 is the output voltage of the subtractor A2, the third voltage V3 is the compensation signal between the third resistor R3 and the first capacitor C1, the fourth voltage V4 is the DC voltage across the second resistor R2, the fifth voltage V5 is the DC operating point voltage of the base terminal of the second power transistor Q2, the first current I1 is the current of the low-frequency voltage-current conversion branch 111, the second current I2 is the current of the high-frequency voltage-current conversion branch 115, and the total current ILD1 is the current of the laser diode LD1.

[0048] The high-frequency voltage-to-current conversion branch 115 includes a second power transistor Q2, a first capacitor C1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a second operational amplifier A3. The first terminal of the first capacitor C1 is connected to the output terminal of the high-frequency signal compensation branch 113, and the second terminal of the first capacitor C1 is connected to the base of the second power transistor Q2. The second resistor R2 is located between the emitter of the second power transistor Q2 and the negative power supply V-. The third resistor R3 is located between the first capacitor C1 and the base of the second power transistor Q2. The first terminal of the fourth resistor R4 is connected to the base of the second power transistor Q2. The non-inverting input terminal of the second operational amplifier A3 is connected to the reference voltage Vref, the inverting input terminal of the second operational amplifier A3 is connected to the emitter of the second power transistor Q2, and the output terminal of the second operational amplifier A3 is connected to the second terminal of the fourth resistor R4.

[0049] The working principle of Example 2 is described below:

[0050] The working principle of the low-frequency voltage-to-current conversion branch 111 and the high-frequency signal compensation branch 113 is basically the same as that in Embodiment 1. The inverting input of the second operational amplifier A3 is connected to the second resistor R2, and the non-inverting input of the second operational amplifier A3 is connected to the reference voltage Vref. The output of the second operational amplifier A3 is connected to the fourth resistor R4.

[0051] The output of the subtractor A2 outputs the second voltage V2, which is transmitted to the third voltage V3 through the first capacitor C1 and then to the third resistor R3. The combined fifth voltage V5 drives the second power transistor Q2 to achieve voltage-to-current conversion, forming a current I2.

[0052] In this second embodiment, the DC stabilization circuit of the high-frequency voltage-to-current conversion branch 115 is controlled by the second operational amplifier A3 in a closed loop. In the closed-loop state, the voltage at the inverting input of the second operational amplifier A3 is equal to the voltage at the non-inverting input, i.e., Vref = V4(DC). The DC operating point current I2(DC) of the high-frequency voltage-to-current conversion branch 115 is Vref / R2. Through the configuration of the second operational amplifier A3, the high-frequency voltage-to-current conversion branch 115 avoids the temperature drift effect of the VBE voltage in the two-power transistor Q2.

[0053] In the high-frequency AC signal branch, the subtractor A2 outputs the second voltage V2, which is converted into the third voltage V3 (AC) through the first capacitor C1. V3 (AC) = V2. V3 (AC) is synthesized into the base AC voltage of the second power transistor Q2 through the third resistor R3 and the fourth resistor R4. That is, the fifth voltage V5 (AC) = V2 (AC) * R3 / (R3 + R4).

[0054] If R1 = R2 is preset, then V5(AC) = V2 * 0.5. Since VBE of the second power transistor Q2 is the voltage drop between the transistor's BE, typically around 0.7V, this DC voltage also short-circuits the high-frequency AC component. Therefore, V4(AC) = V5(AC). The high-frequency AC component of the second current I2 output by the high-frequency voltage-current conversion branch 115 is: I2(AC) = V4(AC) / R2 = 0.5 * V2 / R2.

[0055] If R2 = 0.5 * R1, then I2(AC) = V2 / R1.

[0056] It can be seen that the second voltage V2 output by the subtractor A2 forms a compensating current I2(AC) = V2 / R1 in the high-frequency voltage-to-current conversion branch 115. I2(AC) perfectly compensates for the lack of high-frequency characteristics of the low-frequency voltage-to-current conversion branch 111.

[0057] Finally, combining the analysis of the low-frequency voltage-to-current conversion branch 111 above, it can be concluded that the total current ILD1 flowing through the laser diode LD1 consists of four parts:

[0058] The static operating current I1(DC) of the low-frequency voltage-current conversion branch 111;

[0059] The signal operating current I1(AC) of the low-frequency voltage-current conversion branch 111;

[0060] The static operating current I2 (DC) of the high-frequency voltage-current conversion branch 115;

[0061] The high-frequency voltage-current conversion branch 115 compensates for the AC high-frequency current I2(AC).

[0062] ILD1=I1+I2=I1(DC)+V1 / R1+I2(DC)+V2 / R1.

[0063] I2(AC) = V2 / R1 perfectly compensates for the lack of high-frequency characteristics of the signal operating current V1 / R1 in the low-frequency voltage-current conversion branch 111.

[0064] The technical solution of connecting the high-frequency voltage-to-current conversion branch 115 in parallel with the low-frequency voltage-to-current conversion branch 111 provided in this embodiment can also achieve a very high modulation frequency without temperature drift at the DC operating point. If the first power transistor Q1 is a high-speed transistor, the modulation frequency of the voltage-to-current conversion circuit 11 can reach about 2GHz.

[0065] In another embodiment, the high-frequency voltage-to-current conversion branch 115 can be configured in various ways, but the basic principle is the same: a DC operating point closed loop is used, and the high-frequency AC voltage-to-current conversion is superimposed on the DC operating point closed loop for open-loop operation. Since a low-frequency operational amplifier DC operating point closed-loop circuit is used, high-frequency AC signals above 10 MHz will not affect the closed-loop stability of the DC operating point. Therefore, other connection methods of the high-frequency voltage-to-current conversion branch 115 are not limited here.

[0066] Please continue reading. Figure 5 , Figure 5 This is a schematic diagram of the voltage-to-current conversion circuit provided in Embodiment 3 of this application. The high-frequency signal compensation branch 113 includes a transformer T1 and a second capacitor C2. The first terminal of the second capacitor C2 is connected to the inverting input terminal of the first operational amplifier A1. The two terminals of the primary side of the transformer T1 are respectively connected to the input signal Vin and the second terminal of the second capacitor C2. The two terminals of the secondary side of the transformer T1 are respectively connected to the input terminal of the high-frequency voltage-to-current conversion branch 115 and ground.

[0067] In this third embodiment, the low-frequency voltage-to-current conversion branch 111 and the high-frequency voltage-to-current conversion branch 115 are consistent with other embodiments and share the same basic principle. The high-frequency voltage-to-current conversion branch 115, as previously described, has multiple configuration methods, which are not limited here. In the high-frequency signal compensation branch 113, by configuring the transformer T1 and the second capacitor C2, they cooperate to output the second voltage V2 to the high-frequency voltage-to-current conversion branch 115, where V2 = Vin - V1. The second voltage V2 is input to the high-frequency voltage-to-current conversion branch 115, forming the second current I2 to compensate for the high-frequency signal loss in the low-frequency voltage-to-current conversion branch 111.

[0068] The transformer T1 and the second capacitor C2, together with the low-frequency voltage-to-current conversion branch 111, can also output the high-frequency signal shunted by the low-frequency voltage-to-current conversion branch 111. Based on this, the high-frequency drive current generated by the high-frequency voltage-to-current conversion branch 115 precisely compensates for the insufficient low-frequency drive current of the low-frequency voltage-to-current conversion branch 111, ensuring that the total current of the electro-optical conversion module can reach a very high frequency range.

[0069] Compared with the prior art, the present invention provides a voltage-to-current conversion circuit 11, a transmitter 10, and a signal transmission system 100. The voltage-to-current conversion circuit 11 includes a low-frequency voltage-to-current conversion branch 111, a high-frequency signal compensation branch 113, and a high-frequency voltage-to-current conversion branch 115. The low-frequency voltage-to-current conversion branch 111, by setting the first power transistor Q1 and the first operational amplifier A1, forms a low-frequency signal channel according to the characteristics of the first operational amplifier A1, converting the low-frequency signal Vin entering the low-frequency voltage-to-current conversion branch 111 into a low-frequency drive current. Through the cooperation of the high-frequency signal compensation branch 113 and the high-frequency voltage-to-current conversion branch 115, the input signal Vin enters the high-frequency voltage-to-current conversion branch 115... The high-frequency signal from circuit 115 is converted into a high-frequency drive current. The two currents are superimposed, and the high-frequency drive current of the high-frequency voltage-current conversion branch 115 exactly compensates for the insufficient low-frequency drive current of the low-frequency voltage-current conversion branch 111. After compensation, the total current ILD1 flowing through the electro-optical conversion module 13 can reach a very high frequency range, such as DC-2GHz. The low-frequency voltage-current conversion branch 111 is a closed-loop voltage-current conversion channel with high-precision voltage-current conversion characteristics, ensuring that there is no temperature drift at the DC static operating point. On this basis, the voltage-current conversion circuit 11 does not need to filter the input signal Vin separately, which reduces the cost of circuit design. Moreover, the number of filtering branches is reduced during signal transmission, which increases the accuracy of signal transmission accordingly.

[0070] The above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make improvements without departing from the inventive concept of the present invention, but these improvements all fall within the protection scope of the present invention.

Claims

1. A voltage-to-current conversion circuit, characterized in that, include: The low-frequency voltage-to-current conversion branch, connected to the input signal, includes: First power transistor; and A first operational amplifier, wherein the non-inverting input terminal of the first operational amplifier is connected to the input signal, the inverting input terminal of the first operational amplifier is connected to the emitter of the first power transistor, and the output terminal of the first operational amplifier is connected to the base of the first power transistor. A high-frequency signal compensation branch, wherein the input terminals of the high-frequency signal compensation branch are respectively connected to the non-inverting input terminal and the inverting input terminal of the first operational amplifier; and A high-frequency voltage-to-current conversion branch is connected in parallel with the low-frequency voltage-to-current conversion branch, and the input terminal of the high-frequency voltage-to-current conversion branch is connected to the output terminal of the high-frequency signal compensation branch. The low-frequency voltage-current conversion branch further includes a first resistor, which is located between the emitter of the first power transistor and the negative power supply. The high-frequency voltage-current conversion branch includes: Second power transistor; A first capacitor, wherein a first terminal of the first capacitor is connected to the output terminal of the high-frequency signal compensation branch, and a second terminal of the first capacitor is connected to the base of the second power transistor; and The second resistor is located between the emitter of the second power transistor and the negative power supply.

2. The voltage-to-current conversion circuit according to claim 1, characterized in that, The high-frequency signal compensation branch includes a subtractor. The non-inverting input of the subtractor is connected to the non-inverting input of the first operational amplifier and the input signal. The inverting input of the subtractor is connected to the inverting input of the first operational amplifier and the emitter of the first power transistor. The output of the subtractor is connected to the input of the high-frequency voltage-current conversion branch.

3. The voltage-to-current conversion circuit according to claim 1, characterized in that, The high-frequency signal compensation branch includes: transformer; The second capacitor; the first end of the second capacitor is connected to the inverting input of the first operational amplifier; the two ends of the primary side of the transformer are respectively connected to the input signal and the second end of the second capacitor; the two ends of the secondary side of the transformer are respectively connected to the input of the high-frequency voltage-current conversion branch and ground.

4. The voltage-to-current conversion circuit according to claim 1, characterized in that, The high-frequency voltage-current conversion branch also includes: The third resistor has its first end connected to the positive power supply and its second end connected to the base of the second power transistor. A fourth resistor is connected in series with the third resistor between the positive power supply and the negative power supply, and the first terminal of the fourth resistor is connected to the negative power supply; and A temperature compensation diode, wherein the anode of the temperature compensation diode is connected to the second terminal of the third resistor and the base of the second power transistor, and the cathode of the temperature compensation diode is connected to the second terminal of the fourth resistor.

5. The voltage-to-current conversion circuit according to claim 1, characterized in that, The high-frequency voltage-current conversion branch also includes: The third resistor is disposed between the base of the first capacitor and the base of the second power transistor; A fourth resistor, the first terminal of which is connected to the base of the second power transistor; and The second operational amplifier has its non-inverting input connected to a reference voltage, its inverting input connected to the emitter of the second power transistor, and its output connected to the second terminal of the fourth resistor.

6. A transmitter, characterized in that, include: An electro-optic conversion module, wherein the electro-optic conversion module is a laser diode or a light-emitting diode; A positive power supply is connected to one end of the electro-optical conversion module; Negative power source; and According to any one of claims 1 to 5, the high-frequency voltage-current conversion branch and the low-frequency voltage-current conversion branch are connected in parallel between the electro-optical conversion module and the negative power supply.

7. A signal transmission system, characterized in that, include: Signal receiver; optical fiber; and The transmitter as described in claim 6, wherein the optical fiber is disposed between the transmitter and the signal receiver.

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