Positive / negative skew calibration in cable assembly

Abstract

The present disclosure relates to positive / negative skew calibration in cable assemblies. A cable assembly includes first and second active elements interconnected via a cable, wherein the first active element includes circuitry configured to transmit an original differential signal to the second active element, the original differential signal including a positive (P) side and a corresponding negative (N) side, and circuitry to determine a P / N skew in a corresponding reflected signal, the reflected signal including a portion of the original differential signal reflected from the second active element back to the first active element, the first active element further including circuitry configured to compensate for the determined P / N skew during transmission of a subsequent differential signal.

Description

Priority application

[0001] This patent application claims priority and / or benefit to U.S. Provisional Application No. 63 / 778,224, filed March 26, 2025, entitled “P / N Skew Calibration in Active Cables,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to communication cables, and more specifically to positive / negative skew calibration in cable assemblies. Background Technology

[0003] Generative artificial intelligence (AI) is placing enormous demands on data infrastructure. Given the ever-increasing bandwidth requirements of AI systems, connections are transitioning from 100 gigabits per channel (Gb) to 200 Gb per channel to achieve 1.6 terabits per second (16T) Ethernet. Achieving robust operation at this data transfer rate requires addressing numerous technical challenges, such as improvements in component bandwidth and signal integrity in cabling, connectors, and packaging. Traditionally, data center servers and network equipment rely on copper cabling, known as straight-through cables, for connections within and between racks. Such copper cabling cannot meet the signal integrity requirements at high speeds (e.g., 224 Gbps+). Therefore, data centers are transitioning from straight-through cables to other types of cabling / cable assemblies, including but not limited to active cable (AEC) assemblies. AEC assemblies typically include two active elements containing retimers (one at each end) to improve signal integrity by balancing cable losses; however, at high speeds, the delay mismatch between positive (P) and negative (N) signal transmissions still poses a signal integrity challenge. Therefore, a mechanism is needed for sensing and correcting P / N delay mismatch (i.e., skew). Summary of the Invention

[0004] One aspect of this disclosure provides a cable assembly including a first active element and a second active element interconnected via a cable, wherein the first active element includes circuitry configured to transmit a raw differential signal to the second active element, the raw differential signal including a positive P-side and a corresponding negative N-side; and the circuitry is configured to determine a P / N skew in a corresponding reflected signal, the reflected signal including a portion of the raw differential signal reflected from the second active element back to the first active element, the first active element further including circuitry configured to compensate for the determined P / N skew during subsequent transmission of the differential signal.

[0005] Another aspect of this disclosure provides a method for compensating for P / N skew in an active cable assembly, the active cable assembly including a first active element and a second active element interconnected via a cable, the method comprising: transmitting an original differential signal from the first active element to the second active element, the original differential signal including a positive P side and a corresponding negative N side; detecting P / N skew in a corresponding reflected signal received at the first active element, the reflected signal including a portion of the original differential signal reflected back from the second active element to the first active element; and compensating for the detected P / N skew during the transmission of a subsequent differential signal from the first active element to the second active element.

[0006] Another aspect of this disclosure provides an active cable assembly including a first active element and a second active element interconnected via a cable, wherein the first active element includes circuitry configured to transmit a differential signal to the second active element, the differential signal including a positive P-side and a corresponding negative N-side, and the second active element includes circuitry configured to sense at least one characteristic of the differential signal, the at least one characteristic indicating a delay mismatch between the P-side and the N-side, the second active element further including circuitry configured to transmit the at least one characteristic to the first active element, and the first active element further including circuitry configured to compensate for the delay mismatch during subsequent transmission of the differential signal. Attached Figure Description

[0007] The embodiments will be readily understood from the following detailed description, taken in conjunction with the accompanying drawings. For ease of description, the same reference numerals denote the same structural elements. The embodiments are illustrated in the drawings by way of example and not limitation.

[0008] Figure 1 Various cable assemblies according to some embodiments of this disclosure are shown.

[0009] Figure 2A Example AEC components according to some embodiments of this disclosure are shown.

[0010] Figure 2B Some embodiments according to this disclosure are shown. Figure 2A A schematic diagram of the AEC component is shown.

[0011] Figure 3A and Figure 3B Some embodiments according to this disclosure are shown. Figure 2A A more detailed schematic diagram of the AEC component is shown below.

[0012] Figure 4 and Figure 5 Some embodiments according to this disclosure are shown. Figure 2A The diagram shown illustrates the AEC components, including the relevant paths and engines.

[0013] Figure 6 Example AEC components according to some alternative embodiments of this disclosure are shown.

[0014] Figure 7 An example operational flowchart related to the AEC component is shown according to some embodiments of this disclosure.

[0015] Figure 8 An example operational flowchart related to the AEC component is shown according to some alternative embodiments of the present disclosure. Detailed Implementation

[0016] Overview

[0017] Based on the features of the embodiments described herein, an innovative solution is provided for providing P / N skew detection and calibration in an AEC (Advanced Variable Interference Engine). In a particular embodiment, a random signal is transmitted from a first retimer of the AEC, a portion of which is reflected back to the first retimer by a second retimer of the AEC. At the first retimer, the relevant delays on the P-side and N-side of the reflected signal are measured, and determined based on the differential delay mismatch (i.e., skew). In some embodiments, the skew can be corrected by modifying the transmitting circuitry to apply the skew in the transmitter, thereby applying a correction function for delay mismatch at the transmitting circuitry of the first retimer. In an alternative embodiment, a sensor is provided at the receiving circuitry of the second retimer to sense signal information and provide the information to the transmitting circuitry of the first retimer, the signal information being used to correct the delay mismatch at the transmitting circuitry.

[0018] Brief Reference Figure 1 It should be recognized that the techniques described herein can be advantageously applied to a variety of cable technologies, including but not limited to co-encapsulated copper cable, active copper cable (ACC) 100 and active optical cable (AOC) 102, and active cable (AEC) 104 described herein, without departing from the spirit or scope of the embodiments described herein, and the AEC embodiments described herein are intended to be exemplary only and do not limit the application of the techniques.

[0019] An AOC (e.g., AOC 102) includes a digital signal processor (DSP) as an active element located at both ends of the optical cable, converting electrical signals into optical signals. The optical fiber used is flexible and significantly lighter compared to passive copper cables. AOCs are well-suited for long-distance applications. An ACC (e.g., ACC 100) is a copper cable with re-drivers at both ends as active components. The re-drivers perform signal amplification and equalization. While less flexible than AOCs, ACCs are a more cost-effective and lower-power alternative. As mentioned earlier, a re-timer constitutes the active element of the AEC.

[0020] Exemplary AEC Component

[0021] Figure 2A An exemplary AEC component (or simply AEC) 200 is shown. Figure 2A As shown, the AEC component 200 includes a first timer module 202A and a second timer module 202B, which are integrated with both ends of a coaxial cable 204. According to a specific embodiment, the coaxial cable 204 includes thin coaxial copper cable to extend high-speed (i.e., 56G / 112G+ per channel) signals by 0.5m to over 0.7m, overcoming the distance limitations of passive cables in 400G / 800G / 1.6T data centers. AEC utilizes digital signal processing (DSP)-based retimer technology to clean, amplify, and retime signals, significantly reducing the bit error rate (BER) while providing a thinner, more flexible, and lower-latency alternative to fiber optics. DSP retimers (e.g., retimers 202A, 202B) and forward error correction (FEC) in the connectors minimize jitter, crosstalk, and signal distortion, and the use of high-frequency coaxial conductors (typically 30AWG or thinner) improves signal integrity. Therefore, AEC (such as AEC Component 200) is ideal for high-density AI clusters, top-of-rack (ToR) switching, and PCIe Gen5 / CXL interconnects.

[0022] Compared to direct attach cables, AEC is thinner and offers longer transmission distances (direct attach cables are limited to shorter distances, around 2 meters), while providing lower cost and power consumption than active optical cables, and comparable transmission distance. Active copper cables use retimers to amplify signals, while AEC uses retimers for superior signal regeneration.

[0023] Reference Figure 2B Explain the characteristics of AEC component 200 regarding P / N skew. For example... Figure 2BAs shown, the random differential signal is represented by waveform 220. It should be noted that waveform 220 actually comprises two waveforms: a P-side waveform and an N-side waveform; however, at the transmission point, the P-side waveform and the N-side waveform are substantially aligned, therefore... Figure 2B The signal is represented by a single waveform 220. When the differential signal represented by waveform 220 travels along coaxial cable 204 from the transmitting circuit of one of the timer modules 202A and 202B (in... Figure 2B The data (represented by the digital-to-analog converter (DAC) 222) is transmitted to the receiving circuit of another timer module (in... Figure 2B When the signal is received at the receiver (represented by analog-to-digital converter (ADC) 224), it will experience P / N skew, meaning that either the P-side or N-side of the signal will arrive at the receiver later than the other side. Waveforms 226P and 226N represent the differential signals received at the receiver ADC 224; it should be noted that at the receiver, due to the length of cable 204 and other inherent characteristics of cable 204, there is a delay mismatch d between waveforms 226P and 226N. m Due to impedance mismatch at the receiver, a portion of the signal may be reflected back from the ADC 224, as shown in waveforms 228P and 228N (which also exhibit delay mismatch). m When the reflected signal returns to the DAC 222 in the transmitting circuit, it will experience 2d due to the additional skew introduced as the signal returns to the transmitting circuit along the cable. m The delay mismatch is shown in waveforms 230P and 230N.

[0024] Based on the features of the embodiments described herein, and as will be described in more detail below, a correction function for delay mismatch can be introduced at the transmitting circuit. Alternatively, the transmitting circuit can be modified to apply the skewness for correction within the transmitting circuit.

[0025] Exemplary circuit for P / N skew calibration in AEC

[0026] Now for reference Figure 3A A pseudo-differential transmitter can be used to increase delay mismatch and compensate for cable delay propagation. For example... Figure 3AAs shown, two phase interpolators 300P and 300N are provided to control the P-side and N-side of the transmission phase, respectively. The phase delay (or time delay) in the two phase interpolators (PIs) 300P and 300N will compensate for cable delay mismatch. In a particular embodiment, the PIs 300P and 300N can be rotated so that the signal arriving at the receiving circuit 224 is closer to differential. Rotation of the PI refers to dynamically adjusting the phase shift of the output clock signal, allowing it to move smoothly 360 degrees or more relative to the reference signal. In high-speed serial communication and clock and data recovery (CDR) systems, such rotation can be used to fine-tune the sampling points of the input data, thereby effectively moving the sampling clock in time to maintain optimal alignment (i.e., at the center of the data eye diagram). Rotation is not a static 90-degree offset; rather, rotation means that the control logic can send codes to the PI to output the phase with small offset increments or decrements. The PI typically takes two orthogonal reference clocks (0 degrees and 90 degrees, or I / Q) and mixes them with varying weights (current or voltage) to create an output phase located somewhere between the reference clocks. Rotation means changing the weights to move from 0 degrees to 90 degrees, then from 90 degrees to 180 degrees, and so on. Many PI-based systems are designed for infinite rotation, meaning they can rotate continuously in one direction (clockwise or counterclockwise) without losing lock by going back from 360 degrees to 0 degrees.

[0027] It should be noted that although PI is shown as a means of controlling the phase / time delay of a signal, other devices (such as sensors) and / or techniques may also be employed without departing from the spirit or scope of the embodiments described herein.

[0028] Now for reference Figure 4 and Figure 5 Based on the features of the embodiments described herein, a relevant path can be provided at the transmitting end for performing delay estimation in conjunction with the reflected signal. For example... Figure 4 As shown, the correlation path may include a signal processing circuit device 400 for processing the P-side and N-side of the reflected signal, and providing the processed P-side and N-side signals to the correlation engine 402 to perform delay estimation. Figure 5 As shown, the signal processing circuitry 400 may include a gain stage 500 (in a particular embodiment, the gain stage 500 may be implemented using a variable gain amplifier (VGA) 500), a source follower (SF) 502 for buffering the signal, and an ADC 504 for digitizing the signal and providing the digitized signal to the associated engine 402. The VGA 500 ensures that the input of the ADC 504 has sufficient swing, which may be driven by the SF 502.

[0029] Delay estimation can be performed using matched filters, least mean square (LMS) response, or any other DSP technique. In a particular embodiment, correlation is performed separately for each side (P and N). Subsampling can be used to reduce the ADC's power consumption. Typically, a subsampling ratio of 500 or higher is used, so a low sampling frequency ADC 504 is sufficient for the application described herein.

[0030] In the subsampling correlation engine 402, the data is first digitized using the subsampling ADC 504 and correlated with the original transmitted data. This measures the delay of the return transmission. Since skew exists between the P-side and N-side, two single-ended measurements are required. To achieve single-ended measurements, a switching component 510 is provided to enable differential sampling (by connecting to the main path) and / or single-ended sampling (by connecting to the correlation path). During single-ended sampling, one input of the VGA 500 can be connected to a common-mode voltage using a DC switch, while the other input can be connected to the signal being sampled (e.g., the P-side or N-side). The ADC output is correlated with the original transmitted signal using a matched filter, LMS, or any other DSP technique.

[0031] In a particular embodiment, latency estimation / calibration can be performed during a calibration period prior to the initial use of the AEC component 200 for data transfer between servers. In an alternative embodiment, latency estimation / correlation can be performed at different times throughout the deployment of the AEC component 200.

[0032] Example Alternative Circuit for P / N Skew Calibration in AEC

[0033] Figure 6 Reference to AEC component 600 illustrates alternative embodiments of P / N skew calibration in AEC. For example... Figure 6As shown, the AEC component 600 includes first and second timers 602A and 602B, integrated with a coaxial cable 604. Each timer 602A and 602B includes transmitting circuits 608A and 608B and receiving circuits 610A and 610B. During delay estimation of component 600, P / N skew information about the signal transmitted from transmitting circuit 608A to receiving circuit 610B is detected by sensor 612 and transmitted by transmitting circuit 608B to receiving circuit 610A via the reverse channel of cable 604. Feedback circuit 614 uses the sensor information to control the delay skew of PIs 616P and 616N in a manner similar to that described in the above embodiments. In certain embodiments, the sensor information may include various aspects of received signal quality, including but not limited to transmitter and dispersion eye closure quaternary (TDECQ), amplitude squared coherence (MSC), signal-to-noise ratio (SNDR), and / or BER. This process can be repeated and the delay skew of the PI can be updated until the sensor information indicates that the signal quality is acceptable, at which point component 600 is calibrated.

[0034] The embodiments described herein address both error sensing and correction, wherein error sensing is performed using reflected signal power, and correction is performed using, for example, a PI sensor or a calibration sensor. It should be understood that while the embodiments described herein perform calibration in the transmitting circuitry, calibration can also be performed in the receiving circuitry without departing from the spirit or scope of this disclosure. The embodiments described herein include transmitting a non-differential signal to compensate for cable P / N skew, such that it is fully differential when it reaches the receiver, including circuitry means for generating the non-differential signal in the transmitting circuitry, and adding a delay on the P-side or N-side of the transmission (or more precisely, adding a delay in the clock circuitry used to trigger the DAC) to compensate for cable delay skew. A P / N skew sensing circuit may be included in the transmitting circuitry, operating based on the concept of measuring distance using reflection. A P / N skew sensing circuit may be provided in the receiving circuitry, operating based on the concept of measuring internal metrics such as TDECQ, MSC, SNDR, and / or BER.

[0035] Exemplary Techniques for P / N Skew Calibration in AEC

[0036] Figure 7 This is an example operation flowchart 700 related to P / N skew calibration techniques in an AEC component (e.g., AEC component 200) according to some embodiments of this disclosure. In some embodiments, Figure 7 One or more operations shown can be performed by, for example Figures 2B-5 One or more of the components shown are executed.

[0037] In Operation 702, during an AEC calibration session, a random differential signal is transmitted from the transmitting circuitry of the first timer of the AEC to the receiving circuitry of the second timer of the AEC. It should be understood that an AEC calibration session may occur before the initial deployment of the AEC component in the data center, or at one or more points during the deployment of the AEC component in the data center, depending on the needs of various applications.

[0038] In operation 704, a reflected signal corresponding to the transmitted signal is received at the transmitting circuit of the first timer.

[0039] In operation 706, the P / N skew of the reflected signal is determined (e.g., by the associated engine) at the transmitting circuit of the first timer.

[0040] In operation 708, it is determined whether the P / N skew is zero. If it is, the execution terminates at operation 709, and the P / N skew of AEC is fully compensated; otherwise, the execution proceeds to operation 710.

[0041] In operation 710, the P / N skew determined in operation 706 is compensated at the transmitting circuit of the first timer, and a random differential signal is transmitted to the receiving circuit of the second timer.

[0042] After operation 710 is completed, the process returns to operation 704.

[0043] Although reference Figure 7 The operations shown and described are illustrated as occurring once in a specific order, but it should be understood that the operations can be performed in any suitable order and repeated as needed. Furthermore, one or more operations can be performed in parallel. Figure 7 The operations shown can be combined, or may include more or less detail than described.

[0044] Figure 8 This is an example operation flowchart 800 relating to alternative P / N skew calibration techniques in an AEC component (e.g., AEC component 600) according to some embodiments of the present disclosure. In some embodiments, Figure 8 One or more operations shown can be performed by, for example Figure 6 One or more of the components shown are executed.

[0045] In Operation 802, during an AEC calibration session, a random differential signal is transmitted from the transmitting circuitry of the first timer of the AEC to the receiving circuitry of the second timer of the AEC. It should be understood that an AEC calibration session may occur before the initial deployment of the AEC component in the data center, or at one or more points during the deployment of the AEC component in the data center, depending on the needs of various applications.

[0046] In operation 804, the P / N skew of the transmitted signal is determined at the receiving circuit of the second timer.

[0047] In operation 806, it is determined whether the P / N skew is zero. If it is, the execution terminates at operation 807, and the P / N skew of AEC is fully compensated; otherwise, the execution proceeds to operation 808.

[0048] In operation 808, the P / N skew determined in operation 804 is transmitted from the transmitting circuit of the second timer to the receiving circuit of the first timer via the reverse channel.

[0049] In operation 810, the P / N skew determined in operation 804 is compensated at the transmitting circuit of the first timer, and a random differential signal is transmitted to the receiving circuit of the second timer.

[0050] After operation 810 is completed, the process returns to operation 804.

[0051] Although reference Figure 8 The operations shown and described are illustrated as occurring once in a specific order, but it should be understood that the operations can be performed in any suitable order and repeated as needed. Furthermore, one or more operations can be performed in parallel. Figure 8 The operations shown can be combined, or may include more or less detail than described.

[0052] Selected Example

[0053] Example 1 provides a cable assembly including first and second active elements interconnected via a cable, wherein the first active element includes circuitry configured to transmit a raw differential signal to the second active element, the raw differential signal including a positive (P) side and a corresponding negative (N) side; and circuitry configured to determine a P / N skew in a corresponding reflected signal, the reflected signal including a portion of the raw differential signal reflected from the second active element back to the first active element, the first active element further including circuitry configured to compensate for the determined P / N skew during subsequent transmission of the differential signal.

[0054] Example 2 provides the cable assembly of Example 1, wherein the circuitry configured to compensate for determined P / N skew includes at least one phase interpolator for injecting transmission delay on one of the P-side and N-side.

[0055] Example 3 provides a cable assembly of Example 2, wherein the at least one phase interpolator includes a first phase interpolator for controlling the transmission timing on the P side and a second phase interpolator for controlling the transmission timing on the N side.

[0056] Example 4 provides a cable assembly of any one of Examples 1-3, wherein the first and second active elements include a re-timer or a re-driver, and the cable includes copper cable.

[0057] Example 5 provides a cable assembly of any one of Examples 1-4, wherein the first and second active elements include a digital signal processor (DSP), and the cable includes an optical fiber.

[0058] Example 6 provides a cable assembly of any of Examples 1-5, wherein the first active element further includes a switching component for enabling a correlation path of the first active element, and wherein the correlation path includes a correlation engine for correlating the reflected signal with the original differential signal to determine the P / N skew.

[0059] Example 7 provides the cable assembly of Example 6, wherein the associated path further includes circuitry for processing the reflected signal to be input to the associated engine, and wherein the processing of the P-side of the reflected signal is independent of the N-side of the reflected signal.

[0060] Example 8 provides the cable assembly of Example 7, wherein the circuitry for processing the reflected signal further includes a variable gain amplifier (VGA) for amplifying the reflected signal, a source follower connected to the VGA output to buffer the amplified reflected signal, and an analog-to-digital converter (ADC) for sampling the amplified reflected signal.

[0061] Example 9 provides a method for compensating for P / N skew in an active cable assembly, the active cable assembly including first and second active elements interconnected via cables, the method comprising: transmitting an original differential signal from the first active element to the second active element, the original differential signal including a positive (P) side and a corresponding negative (N) side; detecting P / N skew in a corresponding reflected signal received at the first active element, the reflected signal including a portion of the original differential signal reflected back from the second active element to the first active element; and compensating for the detected P / N skew during the transmission of a subsequent differential signal from the first active element to the second active element.

[0062] Example 10 provides the method of Example 9, further comprising: detecting, at the first active element, an updated P / N skew in a subsequently reflected signal received at the first active element, the subsequently reflected signal including a portion of the subsequently differential signal reflected from the second active element back to the first active element; and determining whether the updated P / N skew is equal to zero.

[0063] Example 11 provides the method of Example 10, further comprising: if the updated P / N skew is not equal to zero, performing compensation, detection, and determination steps until it is determined that the updated P / N skew is equal to zero.

[0064] Example 12 provides a method of any of Examples 9-11, wherein the compensation is performed by at least one phase interpolator to inject transmission delay on one of the P-side and N-side.

[0065] Example 13 provides the method of Example 12, wherein the at least one phase interpolator includes a first phase interpolator for controlling the transmission timing on the P side and a second phase interpolator for controlling the transmission timing on the N side.

[0066] Example 14 provides a method of any of Examples 9-13, and also includes enabling the relevant path of the first active element.

[0067] Example 15 provides the method of Example 14, and further includes using a correlation engine to correlate the reflected signal with the original differential signal to determine the P / N skew.

[0068] Example 16 provides the method of Example 15, further comprising preprocessing the reflected signal prior to the correlation, the preprocessing including amplifying the reflected signal, buffering the amplified reflected signal, and sampling the amplified reflected signal.

[0069] Example 17 provides the method of Example 16, wherein the preprocessing and correlation of the P side of the reflected signal are independent of the N side of the reflected signal.

[0070] Example 18 provides an active cable assembly including first and second active elements interconnected via a cable, wherein the first active element includes circuitry configured to transmit a differential signal to the second active element, the differential signal including a positive (P) side and a corresponding negative (N) side, and the second active element includes circuitry configured to sense at least one characteristic of the differential signal, the at least one characteristic indicating a delay mismatch between the P side and the N side, the second active element further including circuitry configured to transmit the at least one characteristic to the first active element, and the first active element further including circuitry configured to compensate for the delay mismatch during subsequent transmission of the differential signal.

[0071] Example 19 provides an active cable assembly of Example 18, wherein at least one characteristic is transmitted from the second active element to the first active element via a reverse channel of the cable.

[0072] Example 20 provides an active cable assembly of any of Examples 18-19, wherein the circuitry configured to compensate for the delay mismatch includes at least one phase interpolator for injecting transmission delay on one of the P-side and N-side.

[0073] Variations and other instructions

[0074] Detailed descriptions, such as the “Selected Examples” section, provide various examples of the embodiments disclosed herein.

[0075] As used herein, the term "coupled to" or "coupled with" refers to a relationship between electronic components or circuit elements, wherein said components communicate electrically with each other and are capable of transmitting and / or receiving electrical signals between them. The term "coupled to" does not require a direct physical or electrical connection between the coupled components. Rather, "coupled to" can encompass an arrangement in which said components are connected via one or more intermediate elements, components, circuits, or transmission paths. For example, a first component may be "coupled to" a second component, such as an intermediate component (e.g., a resistor, capacitor, inductor, transistor, logic gate, bus, transformer, or other electronic component), or via an intermediate transmission path, while still maintaining the electrical communication capability between the first and second components.

[0076] The foregoing description of the illustrated embodiments of this disclosure, including the content set forth in the abstract, is not intended to be exhaustive or to limit this disclosure to the precise form disclosed. While specific embodiments and examples of this disclosure have been described herein for illustrative purposes, various equivalent modifications can be made within the scope of this disclosure, as will be recognized by those skilled in the art. These modifications can be made to this disclosure based on the detailed description above.

[0077] For illustrative purposes, specific figures, materials, and configurations have been set forth to provide a thorough understanding of the illustrated embodiments. However, it will be apparent to those skilled in the art that this disclosure may be practiced without specific details, and / or may be practiced only in conjunction with some of the described aspects. In other instances, well-known features have been omitted or simplified so as not to obscure the illustrated embodiments.

[0078] Furthermore, reference is made to the accompanying drawings, which form part of this document, illustrating possible implementations. It should be understood that other implementations may be utilized, and structural or logical changes may be made without departing from the scope of this disclosure. Therefore, the following detailed description should not be considered limiting.

[0079] Various operations can be described as a series of discrete actions or operations performed sequentially, in a manner that best facilitates understanding the disclosed subject matter. However, the order in which they are described should not be construed as implying that these operations are necessarily sequentially dependent. Specifically, these operations may not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. In various additional embodiments, additional operations may be performed, or the described operations may be omitted.

[0080] For the purposes of this disclosure, the phrase "A or B" or the phrase "A and / or B" refers to (A), (B), or (A and B). For the purposes of this disclosure, the phrase "A, B, or C" or the phrase "A, B, and / or C" refers to (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). The term "between" when used with a measurement range includes the endpoints of the measurement range.

[0081] The descriptions using the phrases "in one embodiment" or "in an embodiment" can each refer to one or more of the same or different embodiments. The terms "comprising," "including," "having," etc., are synonymous with respect to embodiments of this disclosure. This disclosure may use perspective-based descriptions, such as "above," "below," "top," "bottom," and "side," to interpret various features in the drawings, but these terms are for ease of discussion only and do not imply a desired or desired orientation. The drawings are not necessarily drawn to scale. Unless otherwise stated, the use of ordinal adjectives such as "first," "second," and "third" to describe common objects indicates reference only to different instances of similar objects and is not intended to imply that the objects so described must exist in any particular order, whether temporally, spatially, sequentially, or in any other way.

[0082] In the following detailed description, various aspects of the illustrated embodiments will be described using terminology commonly used by those skilled in the art in order to convey the substance of their work to others skilled in the art.

[0083] The terms “substantially,” “near,” “approximately,” “close to,” and “about” generally refer to within + / - 20% of the target value described herein or known in the art. Similarly, terms indicating various element orientations, such as “coplanar,” “perpendicular,” “orthogonal,” “parallel,” or any other angle between elements, generally refer to within + / - 5 to + / - 20% of the target value described herein or known in the art.

[0084] Furthermore, the terms “comprising,” “including,” “having,” or any other variation thereof are intended to cover non-exclusive inclusion. For example, a method, process, or apparatus that includes a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such a method, process, or apparatus. Additionally, the term “or” refers to an inclusive “or,” not an exclusive “or.”

[0085] The systems, methods, and apparatuses disclosed herein each have several innovative aspects, and no single aspect is solely responsible for all the desirable properties disclosed herein. Details of one or more embodiments of the subject matter described herein are set forth in the specification and accompanying drawings.

Claims

1. A cable assembly including a first active element and a second active element interconnected via a cable, wherein the first active element includes circuitry configured to transmit an original differential signal to the second active element, the original differential signal including a positive P-side and a corresponding negative N-side, and the circuitry configured to determine a P / N skew in a corresponding reflected signal, the reflected signal including a portion of the original differential signal reflected from the second active element back to the first active element, the first active element further including circuitry configured to compensate for the determined P / N skew during subsequent transmission of the differential signal.

2. The cable assembly of claim 1, wherein the circuitry configured to compensate for the determined P / N skew includes at least one phase interpolator for injecting transmission delay with respect to one of the P-side and N-side.

3. The cable assembly of claim 2, wherein the at least one phase interpolator includes a first phase interpolator for controlling the transmission timing on the P side and a second phase interpolator for controlling the transmission timing on the N side.

4. The cable assembly of claim 1, wherein the first active element and the second active element comprise a re-timer or a re-driver, and the cable comprises copper cable.

5. The cable assembly of claim 1, wherein the first active element and the second active element comprise a digital signal processor (DSP), and the cable comprises an optical fiber.

6. The cable assembly of claim 1, wherein the first active element further includes a switching component for enabling a correlation path of the first active element, and wherein the correlation path includes a correlation engine for correlating the reflected signal with the original differential signal to determine the P / N skew.

7. The cable assembly of claim 6, wherein the correlation path further includes circuitry for processing the reflected signal to be input to the correlation engine, and wherein the P-side of the reflected signal is processed independently of the N-side of the reflected signal.

8. The cable assembly of claim 7, wherein the circuitry for processing the reflected signal further comprises a variable gain amplifier (VGA) for amplifying the reflected signal, a source follower connected to the output of the VGA to buffer the amplified reflected signal, and an analog-to-digital converter (ADC) for sampling the amplified reflected signal.

9. A method for compensating for P / N skew in an active cable assembly, the active cable assembly including a first active element and a second active element interconnected via cables, the method comprising: The original differential signal is transmitted from the first active element to the second active element, and the original differential signal includes a positive P side and a corresponding negative N side; Detecting P / N skew in the corresponding reflected signal received at the first active element, the reflected signal including a portion of the original differential signal reflected back from the second active element to the first active element; as well as The detected P / N skew is compensated during the transmission of subsequent differential signals from the first active element to the second active element.

10. The method of claim 9, further comprising: Detect an updated P / N skew in a subsequent reflected signal received at the first active element, the subsequent reflected signal including a portion of the subsequent differential signal reflected back from the second active element to the first active element; as well as Determine whether the updated P / N skew is equal to zero.

11. The method of claim 10, further comprising: If the updated P / N skew is not equal to zero, then the steps of compensation, detection, and determination are performed until it is determined that the updated P / N skew is equal to zero.

12. The method of claim 9, wherein the compensation is performed by at least one phase interpolator for injecting transmission delay with respect to one of the P-side and N-side.

13. The method of claim 12, wherein the at least one phase interpolator comprises a first phase interpolator for controlling the transmission timing on the P side and a second phase interpolator for controlling the transmission timing on the N side.

14. The method of claim 9, further comprising enabling the relevant path of the first active element.

15. The method of claim 14, further comprising using a correlation engine to correlate the reflected signal with the original differential signal to determine the P / N skew.

16. The method of claim 15, further comprising, prior to the correlation, preprocessing the reflected signal, the preprocessing including amplifying the reflected signal, buffering the amplified reflected signal, and sampling the amplified reflected signal.

17. The method of claim 16, wherein the P side of the reflected signal is preprocessed and correlated independently of the N side of the reflected signal.

18. An active cable assembly comprising a first active element and a second active element interconnected via a cable, wherein the first active element includes circuitry configured to transmit a differential signal to the second active element, the differential signal including a positive P-side and a corresponding negative N-side, and the second active element includes circuitry configured to sense at least one characteristic of the differential signal, the at least one characteristic indicating a delay mismatch between the P-side and the N-side, the second active element further including circuitry configured to transmit the at least one characteristic to the first active element, and the first active element further including circuitry configured to compensate for the delay mismatch during subsequent transmission of the differential signal.

19. The active cable assembly of claim 18, wherein at least one characteristic is transmitted from the second active element to the first active element via a reverse channel of the cable.

20. The active cable assembly of claim 18, wherein the circuitry configured to compensate for the delay mismatch includes at least one phase interpolator for injecting transmission delay with respect to one of the P-side and N-side.

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