Circuit for simply realizing backward de-emphasis

Abstract

The invention provides a circuit for simply realizing backward de-emphasis, which consists of a de-emphasis synthesis circuit and a negative feedback branch, and the negative feedback branch comprises a low-pass filter and a negative feedback driving circuit. The backward de-emphasis function of the waveform is realized only by using the low-pass filter, the negative feedback driving circuit and the backward de-emphasis synthesis circuit, and the design is greatly simplified compared with a traditional structure. Compared with the prior art, the circuit area can be effectively saved, the power consumption of the circuit is reduced, and the reliability is improved while the circuit cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of optical communication, and in particular relates to a circuit for simply realizing backward de-emphasis. Background Art

[0002] With the development of optical communication technology, the transmission rate and transmission distance of signals are increasing. Longer transmission channels are usually accompanied by larger insertion loss and poorer channel quality at high frequencies, which causes the high-frequency components of high-speed signals to be greatly damaged during transmission, thereby causing forward and backward crosstalk between symbols and causing signal waveform distortion. The waveform of an ideal signal after transmission through the channel changes as follows: Figure 1 shown.

[0003] In the application scenario where high-speed signals pass through a transmission channel with large losses, the high-frequency components of the signal will produce significant losses while also producing serious backward components. The backward crosstalk caused by the backward components will cause the amplitude of the signal at this moment to affect the amplitude of the signal at later moments, increasing the system's bit error rate. In order to reduce the system bit error rate, it is necessary to obtain a waveform of better quality at the receiving end. Existing technologies usually use backward de-emphasis technology to compensate for the high-frequency signal in advance at the transmitting end, and suppress the generated backward components at the same time. Backward de-emphasis technology is to weaken the amplitude of the backward components generated in other parts of the signal while keeping the amplitude at a certain rising and falling edge of the signal unchanged. The principle of backward de-emphasis technology is as follows: Figure 2 As shown in the figure, the speed of signal level change is proportional to the proportion of high-frequency components in the signal frequency components, that is, the more high-frequency components the signal contains, the faster the signal level flips, and the steeper the rising and falling edges of the signal, so the high-frequency components of the signal mainly appear at the rising and falling edges of the signal. The use of backward de-emphasis technology can effectively compensate for the high-frequency components of the signal lost in the channel. At the same time, backward de-emphasis also weakens the amplitude of the backward component, so that the amplitude of the generated backward crosstalk is reduced, thereby weakening the backward crosstalk.

[0004] The traditional implementation of backward de-emphasis circuit is as follows Figure 3 As shown, the signal passes through the backward branch, forming a phase lag with the main path, and then the waveform is inverted, and then synthesized with the main path signal through a de-emphasis synthesis circuit composed of a Gilbert circuit with a larger weight on the main path, thereby realizing the function of backward de-emphasis. However, the traditional backward de-emphasis circuit requires multiple drivers to form the main path and the backward branch, and the waveform is synthesized in the de-emphasis synthesis circuit to realize the backward de-emphasis function. This structure is relatively complex and will occupy a large area and power consumption, which will not only increase the cost, but also bring difficulties to the heat dissipation design, resulting in reduced circuit reliability. Summary of the invention

[0005] The purpose of the present invention is to provide a circuit for easily implementing backward de-emphasis, so as to solve the technical problems of the prior art mentioned in the above background technology, namely, complex structure, high power consumption and low reliability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A circuit for realizing backward de-emphasis in a simple manner is composed of a backward de-emphasis synthesis circuit and a negative feedback branch, wherein the negative feedback branch includes a low-pass filter circuit and a negative feedback drive circuit.

[0008] Preferably, the backward de-emphasis synthesis circuit is a Gilbert circuit, comprising a main circuit and a feedback branch, and the current of the main circuit is greater than the current of the feedback branch.

[0009] Preferably, the low-pass filter circuit is composed of a resistor connected in series and a capacitor connected in parallel, and the low-pass filter circuit is used to filter out high-frequency components in the emphasized output signal to restore the output signal to a normal signal.

[0010] Preferably, the negative feedback driving circuit is a driving circuit of a current mode structure, and the negative feedback driving circuit is used to shape the restored signal after low-pass filtering into a feedback signal with good waveform quality.

[0011] Furthermore, when the negative feedback branch is not turned on, the input signal is driven to the output end through the backward de-emphasis synthesis circuit, and the waveform remains unchanged; when the negative feedback branch is turned on, the output signal generates a phase delay through the negative feedback branch to form a feedback signal, which is reversely connected to the input end, and then in the main path de-emphasis synthesis circuit with a larger weight, the input signal with a larger weight and the feedback signal with a smaller weight are waveform synthesized to complete the backward de-emphasis function.

[0012] The present invention has the following beneficial effects:

[0013] 1. The backward de-emphasis function of the waveform is realized by only using a low-pass filter, a negative feedback drive circuit and a backward de-emphasis synthesis circuit, which greatly simplifies the design compared with the traditional structure. Compared with the existing technology, it can effectively save circuit area, reduce circuit power consumption, and improve reliability while reducing circuit cost.

[0014] 2. A low-pass filter is used in the negative feedback path to restore the backward de-emphasized signal to ensure that the waveform can be normally synthesized in the backward de-emphasis synthesis circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0016] Figure 1 This is a schematic diagram of the waveform change of an ideal signal after being transmitted through a channel;

[0017] Figure 2 This is the schematic diagram of backward de-emphasis;

[0018] Figure 3 It is a prior art backward de-emphasis circuit;

[0019] Figure 4 It is a structural diagram of a simple backward de-emphasis circuit of the present invention;

[0020] Figure 5 It is a schematic diagram of the backward de-emphasis synthesis circuit;

[0021] Figure 6 It is a schematic diagram of negative feedback driving circuit;

[0022] Figure 7 The figure is a working principle diagram of the simple backward de-emphasis circuit of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] See also Figure 4-7 As shown, a simple circuit for implementing backward de-emphasis has a structure as shown in FIG. Figure 4 As shown, it is composed of a backward de-emphasis synthesis circuit and a negative feedback branch, wherein the negative feedback branch includes a low-pass filter circuit and a negative feedback driving circuit.

[0025] The backward de-emphasis synthesis circuit is a Gilbert circuit, and its structure is shown as follows: Figure 5 As shown, it includes a main circuit and a feedback branch and loads R1 and R2 shared by the two circuits. The main circuit includes a first differential input pair of transistors, namely a first transistor M1, a second transistor M2 and a first tail current source I1, and the feedback branch includes a second differential input pair of transistors, namely a third transistor M3, a fourth transistor M4 and a second tail current source I2.

[0026] In the main path, the gate of the first transistor M1 receives a positive signal Vmain+ from an external input signal, the source of the first transistor M1 is coupled to the input end of the first tail current source I1, the drain of the first transistor M1 is coupled to the first end of the load R1 and serves as the negative output signal end Vout- of the de-emphasis synthesis circuit, and the second end of the load R1 is coupled to the power supply VCC. The gate of the second transistor M2 receives a negative signal Vmain- from an external input signal, the source of the second transistor M2 is coupled to the input end of the first tail current source I1, the drain of the second transistor M2 is coupled to the first end of the load R2 and coupled to the positive output signal end Vout+ of the de-emphasis synthesis circuit, and the second end of the load R2 is coupled to the power supply VCC.

[0027] In the feedback branch, the gate of the third transistor M3 receives the negative feedback signal Vbf- from the negative feedback branch driving circuit, the source of the third transistor M3 is coupled to the input end of the second tail current source I2, and the drain of the third transistor M3 is coupled to the negative output signal end Vout- of the de-emphasis synthesis circuit. The gate of the fourth transistor M4 receives the positive feedback signal Vbf+ from the negative feedback branch driving circuit, the source of the fourth transistor M4 is coupled to the input end of the second tail current source I2, and the drain of the fourth transistor M4 is coupled to the positive output signal end Vout+ of the de-emphasis synthesis circuit.

[0028] The current of the main circuit is greater than the current of the feedback branch, thereby realizing the synthesis of the large-weight input signal waveform and the reverse waveform of the small-weight feedback signal with phase lag, strengthening the rising and falling edge waveforms of the main circuit input signal, and weakening the amplitude of the backward component, thereby realizing the backward de-emphasis function of the input waveform.

[0029] The low-pass filter circuit is composed of a series resistor and a parallel capacitor, which is used to filter out the high-frequency components of the output signal after the backward de-emphasis is completed, restore the signal to its original state without de-emphasis processing, and output it to the negative feedback drive circuit, forming a phase lag with the input signal, ensuring that the feedback signal waveform can be normally synthesized with the input signal in the backward de-emphasis synthesis circuit.

[0030] The negative feedback driving circuit is a driving circuit of a current mode structure, and the current mode (Current Mode Logic, CML) is a level structure based on current. Figure 6As shown, the gate of the fifth transistor M5 receives the positive input signal Vin+ output by the low-pass filter, the source of the fifth transistor M5 is coupled to the input end of the third tail current source I3, and the drain of the fifth transistor M5 is coupled to the first end of the resistor R3 and serves as the negative output end Vout- of the branch driving circuit. The gate of the sixth transistor M6 receives the negative input signal Vin- output by the low-pass filter, the source of the sixth transistor M6 is coupled to the input end of the third tail current source I3, and the drain of the sixth transistor M6 is coupled to one end of the resistor R4 and serves as the positive output end Vout+ of the branch driving circuit. At the same time, the second end of the resistor R3 and the second end of the resistor R4 are both coupled to the power supply, and the output end of the third tail current source I3 is coupled to the ground.

[0031] The negative feedback driving circuit is used to shape the restored signal after low-pass filtering into a feedback signal with better waveform quality.

[0032] Figure 5 , Figure 6 The embodiment of the present invention takes an N-type metal-oxide-semiconductor (NMOS) transistor as an example, but the present invention is not limited thereto, and the transistor may also be an N-type triode, a P-type metal-oxide-semiconductor or a P-type triode, etc. The gate or base of the N-type transistor is also called a control electrode, the source or emitter is also called a first electrode, and the drain or collector is also called a second electrode.

[0033] The working principle of the circuit for realizing backward de-emphasis in the present invention is as follows: Figure 7 As shown, when the negative feedback circuit is not turned on, the input signal is driven to the output end through the de-emphasis synthesis circuit, and the waveform remains unchanged. When the negative feedback circuit is turned on, the output signal forms a phase delay through the negative feedback path, and is reversely connected to the input end. Then, in the de-emphasis synthesis circuit with a larger weight on the main path, the input signal with a larger weight is synthesized with the feedback signal with a smaller weight to complete the backward de-emphasis function. The output signal after de-emphasis passes through the low-pass filter of the feedback branch to filter out the enhanced high-frequency part of the emphasized signal, so that the de-emphasized output signal is restored to a normal signal to ensure the normal synthesis of the waveform. Then, through the same steps as above, the feedback signal and the input signal are continuously synthesized in the backward de-emphasis synthesis circuit to achieve backward de-emphasis of the input waveform.

[0034] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A circuit for simply implementing backward de-emphasis, characterized in that: The invention is composed of a backward de-emphasis synthesis circuit and a negative feedback branch, wherein the negative feedback branch includes a low-pass filter circuit and a negative feedback driving circuit.

2. A circuit for easily implementing backward de-emphasis according to claim 1, characterized in that: The backward de-emphasis synthesis circuit is a Gilbert circuit, comprising a main circuit and a feedback branch, and the current of the main circuit is greater than the current of the feedback branch.

3. A circuit for easily implementing backward de-emphasis according to claim 1, characterized in that: The low-pass filter circuit is composed of a resistor connected in series and a capacitor connected in parallel.

4. A circuit for easily implementing backward de-emphasis according to claim 1, characterized in that: The negative feedback driving circuit is a driving circuit of a current mode structure, and the negative feedback driving circuit is used to shape the restored signal after low-pass filtering into a feedback signal with good waveform quality.

5. A circuit for simply implementing backward de-emphasis according to any one of claims 1 to 4, characterized in that: When the negative feedback branch is not turned on, the input signal is driven to the output end through the backward de-emphasis synthesis circuit, and the waveform remains unchanged; when the negative feedback branch is turned on, the output signal generates a phase delay through the negative feedback branch to form a feedback signal, which is reversely connected to the input end, and then the input signal with a larger weight and the feedback signal with a smaller weight are waveform synthesized in the de-emphasis synthesis circuit with a larger main path weight, thereby completing the backward de-emphasis function.

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