WO2020082262A1

WO2020082262A1 - Limiting amplifier and tia circuit

Info

Publication number: WO2020082262A1
Application number: PCT/CN2018/111641
Authority: WO
Inventors: 劳之豪; 王昕�; 向涛; 商松泉; 袁亚兴; 刘德昂
Original assignee: 深圳市傲科光电子有限公司
Priority date: 2018-10-24
Filing date: 2018-10-24
Publication date: 2020-04-30

Abstract

A limiting amplifier (10), provided with a first input end (11), a second input end (12), a first output end (13), and a second output end (14). The limiting amplifier (10) comprises a first inductor L1, a second inductor (L2), a first load (R1), a second load (R2), a first triode (T1), and a second triode (T2). Collectors of the first triode (T1) and the second triode (T2) are grounded by means of a current source (15), and the first inductor L1 and the second inductor L2 are a pair of differential coupling inductors which are respectively connected in series to the loads (R1, R2). Thus, the limiting amplifier (10) in such a structure has the function of converting a single-ended input signal into a double-ended differential output signal; moreover, the addition of the differential coupling inductors can reduce a phase difference between two output signals, so that the swing of a total output signal is closer to the output of a real differential amplifier.

Description

A limiting amplifier and TIA circuit

Technical field

This application belongs to the technical field of photoelectric communication, and in particular relates to a limiting amplifier and a TIA circuit.

Background technique

In optical sensors and optical fiber communication systems, TIA (Trans-Impedance Amplifier, transimpedance amplifier) belongs to the optical receiver part. TIA is generally used in conjunction with photodiodes, which are used to receive optical signals and convert them into electrical signals. Most electrical signals directly converted into optical signals are relatively weak, so TIA is required to amplify the electrical signals converted by the photodiode. In general, photodiodes convert optical signals into single-ended electrical signals, and TIA only needs to amplify single-ended electrical signals. However, in fiber optic communication systems, for very high-speed signals, TIA must convert single-ended electrical signals into double-ended differential signals, which can increase the signal transmission bandwidth, reduce noise, and better perform the next signal processing.

In the TIA circuit of a typical digital optical fiber communication system receiver, it generally includes modules such as a pre-transimpedance amplifier circuit and a limiting amplifier circuit. The incident light is converted into a photocurrent by a photodiode, and the photocurrent is converted into a single-ended voltage signal by a pre-transimpedance amplifier, and the limiting amplifier's task is to convert the small voltage signal output by the pre-transimpedance amplifier Further enlarge to a sufficiently large amplitude so that the subsequent data decision circuit can work better to reduce the bit error rate. In addition, the CML (Current-Mode Logic) current limiting amplifier is also used as a single-ended to double-ended differential signal converter. Through a DC feedback loop, the single-ended voltage signal is converted into double-ended on the CML limiting amplifier Voltage differential signal. The principle structure diagram of the traditional CML limiting amplifier is shown in Figure 1 (a). The CML limiting amplifier has two input terminals, and the single-ended RF signal RF drives one of the input terminals, while the other input terminal is fixed at a reference voltage. DC. For low-frequency and intermediate-frequency signals, the two output terminals output a pair of very good differential output signals Vp and Vn. But as the frequency increases, for high-frequency signals, the difference in phase and amplitude between the two differential output signals Vp and Vn becomes more and more obvious. As shown in Figure 1 (b), this will cause the differential output swing Vtotal (Vtotal is the vector difference between Vp and Vn) to become smaller, resulting in a reduced opening of the output eye diagram and increased jitter. This phenomenon occurs The reason is because of the signal path of two differential signals: one of the signal RF from the base of the transistor T1 to the collector of T1, and the other DC is from the base of the transistor T2 to the collector of T2, and the transistor T1 works In the state of the common emitter circuit, the transistor T2 works in the state of the common base circuit.

Therefore, when a traditional CML limiting amplifier is connected to a high-frequency signal, the phase and amplitude difference between the two differential output signals output is obvious, the opening of the eye diagram is reduced, and the problem of increased jitter is increased.

technical problem

In view of this, the embodiments of the present application provide a TIA circuit with an improved limiting amplifier structure, which aims to solve the problem that the phase difference between the two differential output signals output when a traditional CML limiting amplifier is connected to a high-frequency signal The amplitude difference is obvious, which leads to the problem that the opening of the eye diagram is reduced and the jitter is increased.

Technical solution

A first aspect of an embodiment of the present application provides a limiting amplifier with a first input terminal, a second input terminal, and a first input. A first aspect of an embodiment of the present application provides a limiting amplifier with a first input Terminal, second input terminal, first output terminal and second output terminal, including:

A first inductor, the first end of the first inductor is connected to a power supply;

A second inductor, a first end of the second inductor is connected to the power supply, and the second inductor and the first inductor are differentially coupled to each other;

A first triode, the base of the first triode is used as the first input end, and the collector of the first triode is connected to the second end of the first inductor through a first load, The collector of the first triode also serves as the first output; and

A second triode, the base of the second triode is used as the second input end, and the collector of the second triode is connected to the second end of the second inductor through a second load, The collector of the second triode also serves as the second output terminal, and the emitter of the second triode and the emitter of the first triode are grounded through a current source.

A second aspect of an embodiment of this application provides a TIA circuit, including:

Pre-transimpedance amplifier;

In the limiting amplifier described above, the first input terminal of the limiting amplifier is connected to the output terminal of the pre-transimpedance amplifier;

An output buffer, two input terminals of the output buffer are connected to two output terminals of the limiting amplifier, and the two output terminals of the output buffer are used as output terminals of the TIA circuit; and

In a feedback loop, two inputs of the feedback loop are connected to two outputs of the output buffer, and an output of the feedback loop is connected to the second input of the limiting amplifier.

Beneficial effect

In order to improve the imbalance between the two output signals, the above-mentioned limiting amplifier adds a pair of differential coupling inductors in series with the load. The addition of differential coupling inductors can reduce the phase difference between the two output signals. The swing of the total output signal is closer to the output of a true differential amplifier. As a result, the opening of the output eye diagram will increase and the jitter will decrease. By properly choosing the time constant, the addition of differential inductors can also increase the -3dB bandwidth of the limiting amplifier. In addition, after adding the inductor, because the two output signals are closer to the true differential signal, the common-mode rejection ratio of the limiting amplifier is improved, and the AC current noise superimposed on the power supply is also suppressed.

BRIEF DESCRIPTION

In order to more clearly explain the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only for the application In some embodiments, for those of ordinary skill in the art, without paying creative labor, other drawings may be obtained based on these drawings.

Figure 1 (a) is a schematic diagram of the circuit structure of a conventional limiting amplifier;

Figure 1 (b) is a vector diagram of two differential output signals of a conventional limiting amplifier;

2 (a) is a schematic diagram of a circuit structure of a limiting amplifier provided by an embodiment of the present application;

Figure 2 (b) is a vector diagram of the two differential output signals of the limiting amplifier shown in Figure 2 (a);

FIG. 3 is a schematic structural diagram of a TIA circuit provided by an embodiment of the present application.

Embodiments of the invention

In order to make the purpose, technical solutions and advantages of the present application more clear, the following describes the present application in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

Referring to FIG. 2 (a), the limiting amplifier 10 provided by the embodiment of the present application has a first input terminal 11, a second input terminal 12, a first output terminal 13 and a second output terminal 14. The limiting amplifier 10 includes a first The inductor L1, the second inductor L2, the first load R1, the second load R2, the first transistor T1 and the second transistor T2.

The first terminal of the first inductor L1 is connected to the power supply Vcc; the first terminal of the second inductor L2 is connected to the power supply Vcc, the second inductor L2 and the first inductor L1 are differentially coupled to each other; the base of the first transistor T1 serves as a limiting amplifier The first input terminal 11 of 10, the collector of the first transistor T1 is connected to the second terminal of the first inductor L1 through the first load R1, the collector of the first transistor T1 also serves as the first An output terminal 13; the base of the second transistor T2 serves as the second input terminal 12 of the limiting amplifier 10, and the collector of the second transistor T2 is connected to the second terminal of the second inductor L2 through the second load R2 The collector of the second transistor T2 also serves as the second output terminal 14 of the limiting amplifier 10. The emitter of the second transistor T2 and the emitter of the first transistor T1 are grounded through the current source 15.

In some embodiments, the second end of the first inductor L1 is the same name end; the first end of the second inductor L2 is the same name end; in other embodiments, the first end of the first inductor L1 may also be the same name end ; The second end of the second inductor L2 is the end of the same name. Optionally, the first load R1 and the second load R2 are circuits composed of at least one of resistance, capacitance, and inductance. In this embodiment, the first load R1 and the second load R2 are one or more series-parallel connected resistors. In other embodiments, the first load R1 and the second load R2 may be in series / parallel inductance / capacitance or the like. The first input 11 of the limiting amplifier 10 is a non-inverting input, the second input 12 is an inverting input, the first output 13 is an in-phase (positive) output, and the second output 14 is an inverting (negative) ) Input terminal.

Optionally, both the first transistor T1 and the second transistor T2 are NPN type. In other embodiments, the first transistor T1 and the second transistor T2 may be PNP transistors or N-channel MOS transistors.

The above-mentioned limiting amplifier 10 is generally a CML limiting amplifier, which adds a pair of differentially coupled inductors L1 and L2 in series with the first load R1 and the second load R2, respectively. The addition of differential coupling inductors can reduce the phase difference between the two differential output signals Vp and Vn, so that the total output signal swing Vtotal (Vtotal is the vector difference of Vp and Vn) is closer to the output of a true differential amplifier ( As shown in Figure 2 (b)). As a result, the opening of the output eye diagram will increase and the jitter will decrease. Moreover, by appropriately selecting the time constant τ = L / R, the addition of the differential coupling inductor can also increase the 3-dB bandwidth of the limiting amplifier 10. In addition, after adding the differential coupling inductor, because the two differential output signals Vp and Vn are closer to the true differential signal, the common mode rejection ratio of the limiting amplifier 10 (Common Mode Rejection Ratio, CMRR) is increased, and the AC current noise superimposed on the power supply Vcc is also suppressed.

Please refer to FIG. 2 (a) and FIG. 3, a TIA circuit provided by an embodiment of the present application includes a pre-transimpedance amplifier 20, the above-mentioned limiting amplifier 10, an output buffer 30 and a feedback loop 40.

The input terminal of the pre-transimpedance amplifier 20 is used as the input terminal of the TIA circuit. The first input terminal 11 of the limiting amplifier 10 is connected to the output terminal of the pre-transimpedance amplifier 20; the two input terminals of the output buffer 30 are The two output terminals of the amplifier 10 are connected, and the two output terminals of the output buffer 30 are used as the output terminals of the TIA circuit; the two input terminals of the feedback loop 40 are connected to the two output terminals of the output buffer 30. The output terminal is connected to the second input terminal 12 of the limiting amplifier 10.

In optical sensors and fiber optic communication systems, the input of the pre-transimpedance amplifier 20 is generally connected to the anode of the photodiode D1, and the cathode of the photodiode D1 is connected to the supply voltage VPD. The incident light is converted into a photocurrent by the photodiode D1, and the photocurrent passes through The pre-transimpedance amplifier 20 converts the single-ended current signal into a single-ended voltage signal. Thereafter, the limiting amplifier 10 converts the single-ended voltage signal into a double-ended voltage differential signal and inputs it to the output buffer 30. Optionally, the limiting amplifier 10 and the output buffer 30 are both CML limiting amplifier and output buffer.

In some embodiments, the TIA circuit further includes a first differential load resistor R3 and a second differential load resistor R4. The first differential load resistor R3 and the second differential load resistor R4 are respectively connected to the two output terminals of the output buffer 30 and Between power supply Vcc1. The first differential load resistor R3 and the second differential load resistor R4 also serve as load resistors at the output of the entire circuit.

In some embodiments, the feedback loop 40 includes an operational amplifier 41, two input terminals of the operational amplifier 41 are respectively connected to two output terminals of the output buffer 30, and the output terminal of the operational amplifier 41 is connected to the second terminal of the limiting amplifier 10 Input terminal 12. Optionally, the two input terminals of the operational amplifier 41 are respectively connected to the two output terminals of the output buffer 30 through a current limiting resistor R5 and a current limiting resistor R6, and the two input terminals of the operational amplifier 41 are directly connected to a filter capacitor C1.

Optionally, the inverting input terminal of the pre-transimpedance amplifier 20 is connected to the anode of the photodiode D1, the non-inverting input terminal of the operational amplifier 41 is connected to the non-inverting output terminal of the output buffer 30, and the inverting input terminal of the operational amplifier 41 is The inverting output terminal of the output buffer 30 is connected.

Various embodiments are described herein for various devices, systems, and / or methods. Many specific details are set forth to provide a thorough understanding of the general structure, function, manufacture, and use of the embodiments as described in the specification and shown in the drawings. However, those skilled in the art will understand that the embodiments may be implemented without such specific details. In other instances, well-known operations, components and elements have been described in detail so as not to obscure the embodiments in the specification. Those skilled in the art will understand that the embodiments shown and described herein are non-limiting examples, and therefore it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the embodiments Scope.

Reference throughout the specification to "various embodiments", "in an embodiment", "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in relation to an embodiment is included in at least In one embodiment. Therefore, the appearance of the phrases "in various embodiments", "in some embodiments", "in one embodiment", or "in an embodiment" in appropriate places throughout the specification does not necessarily refer to the same Implementation. Furthermore, specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Therefore, specific features, structures, or characteristics shown or described in relation to one embodiment may be wholly or partially combined with features, structures, or characteristics of one or more other embodiments without making assumptions that such a combination is not illogical or No functional restrictions. Any direction reference (eg, plus, minus, upper, lower, up, down, left, right, left, right, top, bottom, above, below, vertical, horizontal, straight (Clockwise and counterclockwise) are used for identification purposes to help the reader understand the present disclosure and do not create limitations, especially regarding the location, orientation, or use of the embodiments.

Although certain embodiments are described above with a certain level of detail, those skilled in the art can make many changes to the disclosed embodiments without departing from the scope of the present disclosure. Connection references (eg, attachment, coupling, connection, etc.) should be widely interpreted and may include intermediate members between connections of elements and relative movement between elements. Therefore, a connection reference does not necessarily imply that two elements are directly connected / coupled and in a fixed relationship with each other. The use of "for example" throughout the specification should be widely interpreted and used to provide non-limiting examples of embodiments of the present disclosure, and the present disclosure is not limited to such examples. It is intended that all matters included in the above description or shown in the drawings should be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the disclosure.

Claims

A limiting amplifier has a first input terminal, a second input terminal, a first output terminal and a second output terminal, and is characterized by comprising:

A first inductor, the first end of the first inductor is connected to a power supply;

A second inductor, a first end of the second inductor is connected to the power supply, and the second inductor and the first inductor are differentially coupled to each other;

A first triode, the base of the first triode is used as the first input end, and the collector of the first triode is connected to the second end of the first inductor through a first load, The collector of the first triode also serves as the first output; and

A second triode, the base of the second triode is used as the second input end, and the collector of the second triode is connected to the second end of the second inductor through a second load, The collector of the second triode also serves as the second output terminal, and the emitter of the second triode and the emitter of the first triode are grounded through a current source.
The limiting amplifier according to claim 1, wherein the second terminal of the first inductor is a terminal of the same name and the first terminal of the second inductor is a terminal of the same name.
The limiting amplifier according to claim 1, wherein the first terminal of the first inductor is a terminal of the same name, and the second terminal of the second inductor is a terminal of the same name.
The limiting amplifier according to claim 1, wherein the first load and the second load are circuits composed of at least one of resistance, capacitance and inductance.
The limiting amplifier according to claim 1, wherein the first input terminal is a reverse input terminal, and the second input terminal is a non-inverting input terminal.
The limiting amplifier according to claim 1, wherein the first transistor and the second transistor are both NPN type.
A TIA circuit is characterized by including:

Pre-transimpedance amplifier;

The limiting amplifier according to any one of claims 1 to 6, the first input terminal of the limiting amplifier is connected to the output terminal of the pre-transimpedance amplifier;

An output buffer, two input terminals of the output buffer are connected to two output terminals of the limiting amplifier, and the two output terminals of the output buffer are used as output terminals of the TIA circuit; and

In a feedback loop, two inputs of the feedback loop are connected to two outputs of the output buffer, and an output of the feedback loop is connected to the second input of the limiting amplifier.
The TIA circuit according to claim 7, further comprising a first differential load resistor and a second differential load resistor, the first differential load resistor and the second differential load resistor are respectively connected to the output buffer Between the two output terminals of the converter and the power supply.
The TIA circuit according to claim 8, wherein the feedback loop includes an operational amplifier, two input terminals of the operational amplifier are respectively connected to two output terminals of the output buffer, and the operational The output terminal of the amplifier is connected to the second input terminal of the limiting amplifier.