Driver amplifier

Abstract

The present application provides a driver amplifier circuit. The driver amplifier circuit includes a nonlinear differential amplifier and a nonlinear resistor connected across the output terminals of the differential amplifier. The nonlinear resistor has a resistance value that increases as the magnitude of the differential voltage across the nonlinear resistor increases. A transmitter may include the driver amplifier.

Description

Technical Field

[0001] The present application relates to a driver amplifier circuit, and in particular, but not limited to, to a driver amplifier circuit for a high-speed optical communication system. Background Art

[0002] In transmitters used in optical communications, differential driver amplifiers are used to increase the signal level generated by a high-speed digital signal source in order to properly drive an electro-optical modulator.

[0003] In order to increase the data rate of optical transmitters, a quadrature amplitude modulation (QAM) scheme has been recently introduced in optical communications, which places more stringent requirements on the total harmonic distortion (THD) of the driver amplifier.

[0004] Therefore, any solution that can enable the driver amplifier to have improved THD is worth attention. Summary of the Invention

[0005] In a first aspect, the present application provides a driving amplifier circuit, comprising a nonlinear differential amplifier; and a nonlinear resistor connected across an output end of the differential amplifier, wherein the nonlinear resistor has a resistance value that increases as the differential voltage amplitude across the nonlinear resistor increases.

[0006] The nonlinear resistor counteracts the nonlinearity of the differential amplifier by having a resistance that increases with voltage. Since the output current of the driver amplifier circuit is the difference between the current output of the differential amplifier and the current through the nonlinear resistor, the nonlinearity in the output current can be reduced or eliminated, thereby reducing the total harmonic distortion (THD) of the driver amplifier circuit.

[0007] Furthermore, such a circuit can be constructed to have low parasitic capacitance and, therefore, wide bandwidth. Furthermore, the addition of non-linear resistance does not require any additional biasing, thereby reducing the TH D in the circuit without requiring additional power consumption.

[0008] In one implementation of the first aspect, the nonlinear resistor is configured to sink a voltage-dependent current according to a hyperbolic tangent function. Thus, for low voltage levels, the current increases linearly; but for higher voltages, the current saturates, thereby generating higher-order harmonics that cancel corresponding harmonic content in the differential amplifier signal.

[0009] In one implementation of the first aspect, the nonlinear resistor is configured to subtract a current flowing through the nonlinear resistor from an output current of the nonlinear differential amplifier to provide a current at an output of the driver amplifier circuit that is substantially linear with respect to an input voltage provided at an input of the nonlinear differential amplifier. This subtraction eliminates harmonics and provides a linear signal response for the driver amplifier circuit.

[0010] In one implementation of the first aspect, the nonlinear resistor includes at least one first transistor operating as a two-terminal device. Transistors such as FETs provide a simple and readily available component to provide the nonlinearity required for the nonlinear resistor. For example, when the transistor is a FET (such as a MOSFET), the gate can be connected to the source or drain, so that the FET can operate passively as a nonlinear resistor element (i.e., without the need for a separate bias). In one implementation of the first aspect, the nonlinear resistor also includes a second transistor, which is used as a two-terminal device connected in series with the first transistor. In one implementation, the first transistor and the second transistor are field effect transistors. The gate of the first transistor can be coupled to the gate terminal of the second transistor. Such an implementation is advantageous because the gate of the corresponding transistor does not need to be connected to the output terminal (rail) of the amplifier, and parasitic capacitance associated with the gate can be eliminated or reduced.

[0011] In one implementation of the first aspect, the drain terminal of the first transistor is coupled to the positive output terminal of the differential amplifier, the drain terminal of the second transistor is coupled to the negative output terminal of the differential amplifier; and the source terminals of the first transistor and the second transistor are coupled to the gates of the first transistor and the second transistor. In another implementation, the source terminal of the first transistor is coupled to the positive output terminal of the differential amplifier; the source terminal of the second transistor is coupled to the negative output terminal of the differential amplifier; and the drain terminals of the first transistor and the second transistor are coupled to the gates of the first transistor and the second transistor. In another implementation, the drain terminal of the first transistor is coupled to the positive output terminal of the differential amplifier, the source of the second transistor is coupled to the negative output terminal of the differential amplifier; and the drain terminal of the first transistor and the source terminal of the second transistor are coupled to the gates of the first transistor and the second transistor.

[0012] In one implementation of the first aspect, the driver amplifier circuit further includes a linear resistor connected between the nonlinear resistor and the positive output terminal and / or the negative output terminal of the differential amplifier. Including a resistor between the transistor terminal and an output terminal (such as a rail) of the differential amplifier can provide protection against damaging high currents caused by accidental electrostatic discharge, such as when the circuit is being installed or inspected.

[0013] In a second aspect, a transmitter is provided, comprising a driver amplifier circuit according to any implementation of the first aspect. In one implementation of the second aspect, the transmitter may include an electro-optical modulator configured to modulate an optical signal based on an output of the driver amplifier circuit. Thus, a low THD modulated optical signal can be provided using a power-efficient and high-bandwidth driver. In one example, the transmitter is an optical module or another optical network device.

[0014] In one implementation of the second aspect, the transmitter may include a signal source configured to provide a signal to the driver amplifier circuit. The signal source may be configured to provide a signal modulated according to a quadrature amplitude modulation scheme. For example, in one implementation, the signal source may include a digital-to-analog converter. Thus, data for transmission may be provided as an analog signal, which may be efficiently amplified by the driver amplifier circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0016] Figure 1 A block diagram showing components of a transmitter for a communication system is shown.

[0017] Figure 2 A block diagram showing components of a transmitter according to a communication system is shown.

[0018] Figure 3 Shown is a schematic block diagram showing a transmitter according to an embodiment of the present invention.

[0019] Figure 4a 、 4b 4a and 4c show current-voltage curves corresponding to the differential amplifier, the non-linear differential resistor (NDR), and the output of the driving circuit, respectively, according to an embodiment of the present invention.

[0020] Figure 5 A block diagram of a transmitter according to an embodiment of the present invention is shown, wherein the NDR is composed of a field effect transistor; and

[0021] Figure 6 A block diagram of a transmitter according to an embodiment of the present invention is shown, wherein the NDR is composed of a pair of field effect transistors connected in series;

[0022] Figure 7 A block diagram of a transmitter according to an embodiment of the present invention is shown, wherein the NDR is composed of a pair of field effect transistors connected in series;

[0023] Figure 8 A block diagram of a transmitter according to an embodiment of the present invention is shown, wherein the NDR is composed of a pair of field effect transistors connected in series;

[0024] Figure 9 A block diagram of a transmitter according to an embodiment of the present invention is shown, wherein the NDR is composed of a pair of field effect transistors connected in series, wherein the field effect transistors are coupled to the output rail of a differential amplifier through respective resistors. DETAILED DESCRIPTION

[0025] The following will describe exemplary embodiments in sufficient detail to enable those skilled in the art to embody and implement the systems and processes described herein. It should be understood that the embodiments may be embodied in many different forms and should not be construed as limited to the examples described herein.

[0026] Therefore, the embodiments may be modified in various ways and take various alternative forms, specific embodiments of which are illustrated in the drawings and described in detail below by way of example. This document is not intended to be limited to the specific forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims are intended to be included. In the drawings and in the detailed description, as appropriate, the elements of the exemplary embodiments are always represented by the same reference numerals.

[0027] The terms used herein to describe the embodiments are not intended to limit the scope. The articles "a," "an," and "the" are singular and therefore have a single reference, but the use of the singular in this document should not preclude the presence of a plurality of references. In other words, unless the context clearly indicates otherwise, elements denoted in the singular may be numbered one or more. It is further understood that when used in this specification, the terms "comprises," "includes," and / or "comprises" specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or combinations thereof.

[0028] Unless otherwise defined, all terms used herein (including technical and scientific terms) should be interpreted according to common usage in the art. It is further understood that, unless explicitly defined herein, commonly used terms should also be interpreted as customary terms in the relevant art, rather than idealized or overly formalized meanings.

[0029] Figure 1 1 shows an optical transmitter system 100, which includes a signal source 101, a driver amplifier 102, and an electro-optical modulator 103. The source 101 may include a digital-to-analogue converter (DAC). The DAC may be used to receive a digital signal including a binary data stream and encode the binary data stream into symbols in an analog signal according to an existing modulation scheme. For example, quadrature phase shift keying (QPSK, such as 8-PSK) or quadrature amplitude modulation (QAM, such as 16-QAM, 32-QAM, or 64-QAM) schemes may be used to generate analog signals from a high-speed digital signal source. Simpler schemes such as return-to-zero (RZ) or non-return-to-zero (NRZ) and on / off keying (OOK) may be used alternatively or additionally. The selected scheme may depend on the required spectral efficiency and the complexity of the source providing the signal modulated by the electro-optical modulator 103.

[0030] Driver amplifier 102 is an electrical signal amplifier for receiving an analog electrical signal from signal source 101 and amplifying the analog electrical signal to a level suitable for inducing modulation at electro-optical modulator 103. A typical driver amplifier is a differential amplifier having differential inputs and outputs (ie, a fully differential amplifier).

[0031] The electro-optic modulator 103 utilizes the electro-optic effect to modulate the phase of light passing through the modulator. For example, the light can pass through a crystal (such as lithium niobate) having a refractive index that depends on the strength of the local electric field. The local electric field can be modulated by the signal output by the driver 102 to modulate the light. In one embodiment, the electro-optic modulator 103 may include one or more Mach-Zehnder electro-optic modulators for appropriately modulating the I and Q components, for example, for transmitting QPSK or QAM signals. Other types and topologies, technologies, and materials of electro-optic modulators will be understood by those skilled in the art.

[0032] For example, the transmitter can be provided in any optical communication device in an optical network. One example of an optical communication device is an optical module. An optical module is a hot-swappable transmitter (or transceiver) used for high-bandwidth data communication applications (such as greater than 10 Gbit / s).

[0033] Figure 2 A scheme for reducing the THD of driver amplifier 102 is shown. Driver amplifier 102 has differential input terminals (IN+ and IN-) connected to source 101 and differential output terminals (OUT+ and OUT-) connected to electro-optical modulator 103. Driver amplifier 102 is composed of two circuit elements, a primary driver 201 and a secondary driver 202. The differential input signal from source 101 is split between the differential inputs (MD_IN+ and MD_IN-) of primary driver 201 and the differential inputs (SD_IN+ and SD_IN-) of secondary driver 202.

[0034] The differential outputs of the primary driver (MD_OUT+ and MD_OUT-) and the secondary driver (SD_OUT+ and SD_OUT-) are connected in antiphase. That is, the primary driver's positive output terminal, MD_OUT+, is connected to the secondary driver's negative output terminal, SD_OUT-, and the primary driver's negative output terminal, MD_OUT-, is connected to the secondary driver's positive output terminal, SD_OUT+. Primary driver 201 is designed to linearly amplify input signals at operating frequency "f." However, due to the THD of primary driver 201, the primary driver also generates higher-order harmonics ("2f, 3f, ..."). These higher-order harmonics typically have lower amplitudes relative to the operating frequency "f."

[0035] The secondary driver 202 is designed to exhibit strong nonlinearity. Therefore, for a small amplitude operating frequency component "f", higher amplitude signal components for higher order harmonics ("2f, 3f, ...") are generated. Since the outputs MD_OUT+, MD_OUT- of the main driver 201 are connected in anti-phase to the SD_OUT+, SD_OUT- of the secondary driver, as a result, the component with the operating frequency "f" and the higher order harmonic components ("2f, 3f, ...") of the signal output from the secondary driver 202 are subtracted from the signal output from the main driver 201. Since the amplitude of the main driver "f" is much higher than the amplitude of the secondary driver output signal "f", the final amplitude of the operating frequency component "f" reaching the electro-optical modulator is only slightly smaller than the signal component of the frequency "f" generated by the main driver 201. At the same time, since the amplitudes of the higher-order harmonics ("2f, 3f, ...") output by the primary driver are similar to those of the higher-order harmonics ("2f, 3f, ...") output by the secondary driver, the final amplitudes of the higher-order harmonics ("2f, 3f, ...") reaching the electro-optical modulator are close to zero. As a result, the THD level of the signal provided to the electro-optical modulator input is very low.

[0036] However, this approach has many disadvantages. These disadvantages include:

[0037] 1) Higher power consumption: The secondary driver 202 requires biasing and therefore consumes DC power, thereby increasing the overall power consumption of the driver amplifier circuit 102 .

[0038] 2) Reduced bandwidth: The secondary driver 202 increases the input and output parasitic capacitance of the driver, thereby reducing the maximum operating frequency of the driver amplifier circuit 102. This may make it unsuitable for high data rate applications.

[0039] In short, Figure 2 The scheme described in

[15] can improve THD, but at the expense of higher power consumption and reduced operating bandwidth.

[0040] Figure 3 One embodiment is shown in FIG. 1 , which shows a driver amplifier 102 that uses a non-linear differential resistor (NDR) 302 to effectively linearize the output of the driver amplifier and provide a low THD output signal to the electro-optic modulator 103 .

[0041] Specifically, if Figure 3As shown, the driver amplifier has a single differential amplifier as driver 301. Source 101 provides differential input signals at inputs IN+ and IN- of driver 301, and driver 301 provides differential outputs at positive and negative output rails (terminals) 301a and 301b, respectively. In other words, driver 301 can be a fully differential amplifier according to one embodiment. A nonlinear differential resistor (NDR) is added between the output terminals of driver 301, that is, between output rails 301a and 301b of driver 301. The differential signal (OUT+, OUT-) across NDR is provided from the output of driver amplifier 102 to electro-optical modulator 103. As shown, driver current IDRIVER flows between the terminals of driver 301. A portion of driver current IDRIVER flows through NDR as INDR, and the remainder flows through the electro-optical modulator as differential signal output current IOUT. The primary behavior or characteristic of a non-linear differential resistor is that the resistance of the NDR increases as the voltage drop across its terminals 302a, 302b increases.

[0042] Figure 3 The functional characteristics of the circuit in FIG4 can be explained by referring to the current-voltage characteristics shown in FIG4(a), (b), and (c). The differential output current (IDRIVER) of the driver has a behavior 401 as shown in FIG4(a), where the horizontal axis represents the differential input voltage (VIN=)VIN+-VIN- and the vertical axis represents the current IDRIVER. For small amplitude levels of VIN, the current increases substantially linearly with respect to VIN, and then IDRIVER begins to saturate at higher amplitude levels due to the generation of higher-order harmonics. The current flowing through the nonlinear differential resistor NDR (INDR) has a behavior 402 as shown in FIG4(b). As for the driver current IDRIVER, for small amplitude levels of VIN, the current INDR also increases substantially linearly with respect to the input voltage VIN across its terminals, and then saturates due to the generation of higher-order harmonics. The final differential output current (IOUT) reaching the electro-optic modulator is the difference between the connection and INDR, resulting in the current-voltage characteristic 403 shown in FIG4(c). As shown, the output current IPUT is substantially linear with respect to the input voltage VIN, resulting in a very low THD level. In other words, by connecting the NDR 302 across the output terminals of the driver (differential amplifier) 301, the current INDR flowing through the NDR 302 is subtracted from the output current of the differential amplifier 301 to provide a current output of the driver (differential amplifier) 301 that is substantially linear with respect to the input voltage Vin.

[0043] Therefore, by appropriately designing the NDR 302 response, nonlinearities in the driver output current can be offset and the output of the driver amplifier 102 can be linearized to provide very low THD. According to an embodiment, the current-voltage characteristic of the NDR 302 can be considered a hyperbolic tangent function. By selecting or designing an appropriate circuit to approximate or replicate this behavior, the desired cancellation of harmonic distortion present in the driver 301 can be achieved. Furthermore, the use of such a nonlinear differential resistor eliminates the need for bias current and voltage, thereby not increasing overall power consumption. Furthermore, the input / output parasitic capacitance of the nonlinear differential resistor circuit 302 can be designed to be much lower than that of a driver such as a differential amplifier, thereby not negatively impacting the bandwidth of the driver amplifier circuit 102. Therefore, the use of the NDR 302 enables the driver amplifier circuit 102 to have very low THD levels without increasing power consumption and / or reducing operating bandwidth.

[0044] Various embodiments will now be described that illustrate electronic circuit elements or combinations of circuit elements that will provide the desired behavior of NDR 302. However, the present invention is not limited to these embodiments, and other circuits that provide a behavior that increases resistance with voltage, such as according to a hyperbolic tangent function, or other functions that provide at least a portion of the characteristics that negate the THD of driver 301, are contemplated.

[0045] Figure 5 An embodiment of a driver amplifier circuit 102 is shown in which NDR is implemented using a field effect transistor (FET) 501. The gate and drain of the FET are coupled together, causing the FET to operate as a two-terminal resistive device. When the FET is configured as a resistor in this manner, the nonlinearity of the FET response can provide the desired NDR characteristics. The coupled gate (G) and drain (D) terminals are connected to the negative differential output rail 303b, while the source (S) is connected to the positive output rail 303a.

[0046] Due to the symmetry exhibited in setting up the transistor, according to a further embodiment, the polarity of FET 501 can be reversed so that the gate (G) and drain (D) are connected to the positive rail 303a and the source (S) is connected to the negative rail 303b.

[0047] A consequence of using a single FET 501 arranged in this manner to provide NDR 302 is that the gate capacitance of FET 501 is parasitic to driver circuit 102 , potentially reducing the operating bandwidth due to FET 501 being connected to the output rail of driver 301 .

[0048] Figure 6An embodiment is shown in which a nonlinear differential resistor NDR is implemented by two first and second FET transistors 601, 602 (Q1 and Q2) connected in series back to back. The drain (D) of the first FET 601 is connected to the positive rail 301a (D_OUT+) and the drain (D) of the second FET 602 is connected to the negative rail 301b (D_OUT-). The gate (G) and source (S) terminals of the first and second FETs 601, 602 are connected together. Thus, the first and second FETs each act as a two terminal device and, because they are connected in series together, act as a single nonlinear resistor. This dual transistor embodiment has advantages over Figure 5 In this embodiment, for example, since the gate terminal of FET 601 or FET 602 is connected to the output terminal of driver 301 , parasitic capacitance that may reduce the operating bandwidth is avoided.

[0049] Another example is Figure 7 As shown, the drain (D) and source (S) terminals of the first and second FETs 601 and 602 (Q1 and Q2) implementing the nonlinear resistance are reversed, such that the source (S) terminal of the first FET 601 (Q1) and the source (S) terminal of the FET 602 (Q2) are connected to the positive drive rail 301a (D_OUT+), and the source (S) terminal of the second FET 602 (Q2) is connected to the negative drive rail 301b (D_OUT-). The gate (G) and drain (D) of the first and second FETs 601 and 602 are connected together. This is possible, for example, because the polarity of the FETs configured at both ends is not important due to the symmetry of the electrical characteristics.

[0050] Another example is Figure 8 As shown, the FETs 601 and 602 have the same polarity such that the drain (D) of the first FET 601 (Q1) is connected to the positive rail 301a (D_OUT+) and the source (S) of the second FET 602 (Q2) is connected to the negative rail 301b (D_OUT-). The gates (G) of the first and second FETs 601, 602 are connected to the source of the first FET 601 (Q1) and the drain (D) of the second FET 602 (Q2). In this embodiment, Figure 6 Compared to the embodiment shown, the terminals of the second FET 602 (Q2) are inverted, but according to another embodiment, if the terminals of the first FET 601 (Q1) are inverted, and the terminals of Q2 remain the same Figure 6 The same state of the embodiment can also achieve the same result.

[0051] Another example is Figure 9 As shown, this embodiment is Figure 6, however, two resistors 901, 902 (R1 and R2) are inserted between the connection terminals 302a, 302b of the NDR and the corresponding output rails 301a, 301b of the driver 301. The resistors can have the same value or different values. The resistors 901, 902 (R1 and R2) serve to effectively fix the amount of current that flows through the circuit, thereby protecting the circuit elements (e.g., the FETs 601, 602) from damage due to electrostatic discharge. For example, when installing or measuring a driver amplifier circuit, such a discharge may occur due to electrostatic discharge from the measuring or installation instrument. The resistance value of the NDR may be very low, which means that in the event of such an electrostatic discharge, a large and destructive current may flow through the circuit. The linearity of the resistors 901, 902 may reduce the benefit obtained from the elimination of THD because it reduces the nonlinearity of the NDR to some extent, but by carefully selecting the values of the resistors 901, 902, it can be managed so that a substantial benefit in reducing THD is obtained while still protecting the circuit 102 from electrostatic discharge. Although Figure 9 The NDR 302 in is shown as Figure 6 The two FETs 601, 602 of the embodiment are configured, but it should be understood that the protection resistors 901, 902 (R1 and R2) can be used with other implementations of NDR, such as Figure 5 Single transistor implantation.

[0052] In the above embodiments, the NDR is composed of one or more FETs, such as n-type or p-type MOSFETs. However, as will be appreciated, other transistor elements may be used instead. For example, a bipolar junction transistor may be used, or a junction field-effect transistor may be provided, provided that a resistance that increases with voltage behavior can be provided, i.e., by configuring the transistor (or other circuit element) as a nonlinear two-terminal device.

[0053] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0054] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0055] In the embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, unit division is merely a logical function division, and other divisions may be used in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be implemented through some interfaces. The indirect coupling or communication connection between devices or units can be implemented in electrical, mechanical or other forms.

[0056] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0057] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0058] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be implemented in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for instructing a computer device (which can be a personal computer, server network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: any medium that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0059] The present application may be embodied in other specific devices and / or methods. The described embodiments should be considered in all respects as illustrative and not restrictive. In particular, the scope of the present application is indicated by the appended claims rather than by the description and drawings herein. Any changes that come within the meaning and range of equivalents of the claims are intended to be included within their scope.

Claims

1. A driving amplifier circuit, characterized in that: include: Nonlinear differential amplifier; as well as a nonlinear resistor connected across the output terminal of the differential amplifier, The nonlinear resistor has a resistance value that increases as the amplitude of the differential voltage across the nonlinear resistor increases, and the nonlinear resistor is configured to absorb a voltage-dependent current according to a hyperbolic tangent function.

2. The circuit according to claim 1, wherein: The nonlinear resistor is configured such that a current flowing through the nonlinear resistor is subtracted from an output current of the nonlinear differential amplifier to provide a current at the output of the driver amplifier circuit that is substantially linear with respect to an input voltage provided at an input of the nonlinear differential amplifier.

3. The circuit according to claim 2, characterized in that The nonlinear resistor includes at least one first transistor operating as a two-terminal device.

4. The circuit according to claim 3, characterized in that The nonlinear resistor also includes a second transistor that functions as a two-terminal device connected in series with the first transistor.

5. The circuit according to claim 4, characterized in that The first transistor and the second transistor are field effect transistors.

6. The circuit according to claim 5, characterized in that The gate of the first transistor is coupled to the gate terminal of the second transistor.

7. The circuit according to claim 6, characterized in that a drain terminal of the first transistor coupled to a positive output terminal of the differential amplifier, A drain terminal of the second transistor is coupled to a negative output terminal of the differential amplifier; and Source terminals of the first transistor and the second transistor are coupled to gates of the first transistor and the second transistor.

8. The circuit according to claim 6, characterized in that a source terminal of the first transistor coupled to a positive output terminal of the differential amplifier; A source terminal of the second transistor is coupled to a negative output terminal of the differential amplifier; and Drain terminals of the first transistor and the second transistor are coupled to gates of the first transistor and the second transistor.

9. The circuit according to claim 6, characterized in that a drain terminal of the first transistor coupled to a positive output terminal of the differential amplifier, A source of the second transistor is coupled to a negative output terminal of the differential amplifier; and A drain terminal of the first transistor and a source terminal of the second transistor are coupled to gates of the first transistor and the second transistor.

10. The circuit according to any one of claims 6 to 9, characterized in that The circuit further includes a linear resistor connected between the non-linear resistor and a positive output terminal and / or a negative output terminal of the differential amplifier.

11. A transmitter, characterized in that: The device comprises a driver amplifier circuit according to any one of claims 1 to 10.

12. The transmitter according to claim 11, characterized in that The transmitter also includes an electro-optical modulator for modulating the output of the driver amplifier circuit.

13. The transmitter according to claim 12, characterized in that The transmitter further includes a signal source configured to provide a signal to the driver amplifier circuit.

14. The transmitter according to claim 13, characterized in that The signal source is used to provide a signal modulated according to a quadrature amplitude modulation scheme.

15. The transmitter according to claim 13 or 14, characterized in that The signal source includes a digital-to-analog converter.

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