Circuit for simply realizing forward de-emphasis

Abstract

The invention provides a circuit for simply realizing forward de-emphasis, which consists of a forward de-emphasis synthesis circuit and a negative feedback branch, and the negative feedback branch comprises a low-pass filter circuit and a negative feedback driving circuit. The forward de-emphasis function of the waveform is realized only by using the low-pass filter, the negative feedback driving circuit and the forward 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 forward de-emphasis. Background Art

[0002] With the development of optical communication technology, the transmission rate and distance of signals are increasing. Longer transmission channels are usually accompanied by greater insertion loss and poorer channel quality at high frequencies, which will cause the high-frequency components of high-speed signals to be greatly damaged during transmission, thereby causing forward and forward 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 reflections due to impedance discontinuities, the amplitude of the high-frequency component of the signal will be greatly lost due to poor return loss. At the same time, a forward component will be generated, causing serious forward crosstalk. The forward crosstalk will cause the amplitude of the signal at this moment to affect the amplitude of the signal at the previous moment, resulting in an increase in the system 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. The existing technology usually uses forward de-emphasis technology to compensate for the high-frequency signal in advance at the transmitting end, and suppress the generated forward component at the same time. Forward de-emphasis technology is to reduce the amplitude of the signal and the generated forward component in other places while keeping the amplitude of the signal unchanged at a certain rising and falling edge. The principle of forward 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. The more high-frequency components a signal contains, the faster the signal level flips and the steeper the rising and falling edges of the signal. Therefore, the high-frequency components of the signal mainly appear at the rising and falling edges of the signal. The forward de-emphasis technology can effectively compensate for the high-frequency components of the signal lost due to reflection in the channel. At the same time, the forward de-emphasis also weakens the amplitude of the forward component, so that the amplitude of the generated forward component is lowered, thereby reducing the forward crosstalk.

[0004] The traditional forward de-emphasis circuit implementation is as follows Figure 3 As shown, the signal passes through the forward branch and forms a phase advance with the main path, 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 branch weight, thereby realizing the forward de-emphasis function. However, the traditional forward de-emphasis circuit requires multiple drivers to form the main path and the forward branch, and synthesizes the waveform in the de-emphasis synthesis circuit to realize the forward de-emphasis function. This structure is relatively complex, occupies a large area and consumes power, which not only increases the cost, but also brings 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 simply implementing forward 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 forward de-emphasis in a simple manner is composed of a forward 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 forward de-emphasis synthesis circuit is a Gilbert circuit, comprising a feedback branch and a main circuit, and the current of the feedback branch is greater than the current of the main circuit.

[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 forward 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 waveform of the large-weight feedback signal and the small-weight input signal are synthesized in the de-emphasis synthesis circuit with a larger branch weight to complete the forward de-emphasis function, and then the polarity is reversed through the reverse connection of the differential transmission line, so that the final output signal remains in the same direction as the input signal.

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

[0013] 1. The forward de-emphasis function of the waveform is realized by only using a low-pass filter, a negative feedback driving circuit and a forward de-emphasis synthesis circuit, which greatly simplifies the design compared with the traditional structure. Compared with the existing technology, this invention 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 forward de-emphasized signal to ensure that the waveform can be normally synthesized in the forward 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 forward de-emphasis;

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

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

[0020] Figure 5 It is a schematic diagram of the forward 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 simplified forward 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 forward de-emphasis has a structure as shown in FIG. Figure 4 As shown, it is composed of a forward 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 forward de-emphasis synthesis circuit is a Gilbert circuit, and its structure is shown as follows: Figure 5 As shown, it includes a feedback branch and a main path and loads R1 and R2 shared by the two paths. The feedback branch 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 main path 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 feedback branch, the gate of the first transistor M1 receives the feedback positive signal Vbf+ from the negative feedback branch driving circuit, 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 the feedback negative signal Vbf- from the negative feedback branch driving circuit, 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 main path, the gate of the third transistor M3 receives a negative signal Vmain- from an external input signal, 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 a positive signal Vmain+ from an external input signal, 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 feedback branch is greater than the current of the main circuit, thereby realizing the synthesis of the reverse waveform of the feedback signal with a large weight and a phase lag and the input signal waveform with a smaller weight, strengthening the rising and falling edge waveforms of the branch feedback signal, and weakening the forward crosstalk signal, thereby realizing the forward 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 component of the output signal after the forward 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 forward 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 forward 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 branch weight, the feedback signal with a large weight is synthesized with the input signal with a smaller weight to complete the forward de-emphasis function. The de-emphasized output signal 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. After the same steps as above, the feedback signal and the input signal continue to synthesize the waveform in the forward de-emphasis synthesis circuit to achieve forward de-emphasis of the input waveform. Subsequently, the polarity is reversed through the reverse connection of the differential transmission line, so that the final output signal remains in the same direction as the input signal.

[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 forward de-emphasis, characterized in that: The invention is composed of a forward 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 simply implementing forward de-emphasis according to claim 1, characterized in that: The forward de-emphasis synthesis circuit is a Gilbert circuit, comprising a feedback branch and a main circuit, and the current of the feedback branch is greater than the current of the main circuit.

3. A circuit for simply implementing forward 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 simply implementing forward 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 forward 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 forward 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 feedback signal with a large weight is synthesized with the input signal with a small weight in the de-emphasis synthesis circuit with a larger branch weight to complete the forward de-emphasis function, and then the polarity is reversed through the reverse connection of the differential transmission line, so that the final output signal remains in the same direction as the input signal.

Images