Differential skew generation apparatus and differential skew generation method

Abstract

To enable varying a skew amount without performing a mechanical operation.SOLUTION: A differential skew generation device 1 includes: a clock oscillator 2 for oscillating and outputting a clock signal; a first pattern generator 4A having a first output terminal 11A that outputs a positive signal to an evaluation target W at timing of a signal in which a phase angle is adjusted by IQ modulation of the clock signal, and a second output terminal 12A to which a terminator 5A is connected; and a second pattern generator 4B having a first output terminal 11B to which a terminator 5B is connected, and a second output terminal 12B that outputs a negative signal to the evaluation target W at timing of a signal in which a phase angle is adjusted by IQ modulation of the clock signal. The first pattern generator 4A and the second pattern generator 4B operate in synchronization with each other and allocate an integer unit of a UI of a set skew amount to transmission timing shift and a decimal unit as IQ modulation to control.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a differential skew generation device and a differential skew generation method for generating a differential skew, which is a time difference between a positive signal and a negative signal input to an evaluation target.

Background Art

[0002] Since differential transmission is excellent in resistance to common mode noise, many of high-speed serial communications that require high waveform quality use differential transmission. Since differential transmission assumes that the arrival timings of the positive signal and the negative signal are equal, if the timing deviation (skew) is not sufficiently small, its effect cannot be exerted, and rather, it has an adverse effect.

[0003] Particularly when differential signals pass through a differential line, capacitive, inductive, or a combined coupling occurs between the positive signal and the negative signal. Therefore, skew causes distortion and reflection in each other's signals, greatly degrading the waveform quality.

[0004] In recent high-speed serial communications, a higher modulation rate and multilevel modulation techniques are used. For example, in PCIe Gen6, a modulation method of 32Gbaud PAM4 is adopted. Accordingly, since the requirements for waveform quality have become more severe, the importance of evaluating the influence of skew on transmission lines and devices has increased. Note that Patent Document 1 below discloses a technique related to skew adjustment.

[0005] By the way, as one of the methods for evaluating the above-described skew, a mechanical delay adapter, which is a device that mechanically varies the line length of a coaxial line, can be cited.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, because mechanical delay adapters are operated mechanically, they have limitations in reproducibility, resolution, and variable range, and are unsuitable for automation. While there are types with wider variable ranges, in that case there is a trade-off with resolution, and it is difficult to achieve both variable range and resolution simultaneously. Also, since inserting a mechanical delay adapter itself affects the transmission characteristics, the measurer needs to carefully examine the measurement results to determine whether the effect is due to the mechanical delay adapter or skew. Although the effects of the frequency characteristics and insertion loss of the mechanical delay adapter can be largely eliminated by calibrating the end face of the mechanical delay adapter, the calibration end face changes depending on the operation of the mechanical delay adapter, so phase calibration cannot be strictly maintained. Coupling and reflections that occur on the transmission line often have the line length (phase) as one parameter, and since this changes depending on the operation, it is difficult to isolate the effect of skew.

[0008] Therefore, the present invention has been made in view of the above problems, and aims to provide a differential skew generation device and a differential skew generation method that can vary the differential skew to a desired amount without performing any mechanical operation. [Means for solving the problem]

[0009] To achieve the above objective, the differential skew generation device described in claim 1 of the present invention includes a clock oscillator 2 that outputs a clock signal, It has a first output terminal 11A that outputs a positive signal to the evaluation target W at the timing of a signal obtained by IQ modulating the clock signal and adjusting the phase angle, and a second output terminal 12A to which the terminator 5A is connected. It also includes a first IQ modulator 13A, a first pattern generation unit 14A, and a first control unit 15A. The first signal generator 4A and The terminal 5B is connected to 3The output terminal 11B and the terminal that outputs a negative signal to the evaluation target at the timing of the signal obtained by IQ modulating the clock signal and adjusting the phase angle. 4 It has an output terminal 12B. It also includes a second IQ modulator 13B, a second pattern generation unit 14B, and a second control unit 15B. It comprises a second signal generator 4B, The first and second signal generators operate synchronously and perform a transmission timing shift, which shifts the signal transmission timing by an integer unit of the set skew amount UI. to , the fractional unit of the UI of the set skew amount is used for IQ modulation each Distribution 、 When the skew amount in units of UI is set, the first control unit distributes the required IQ modulation amount and transmission timing shift amount and controls at least one of the first IQ modulator and the first pattern generation unit. When the skew amount in units of UI is set, the second control unit distributes it to the required IQ modulation amount and transmission timing shift amount, and then controls the second IQ modulator and the second pattern generation unit. The invention is characterized by performing control of at least one of the following:

[0010] The differential skew generation apparatus described in claim 2 of the present invention is the differential skew generation apparatus of claim 1, When the amount of skew is set in units of time, the amount of skew set in units of time and The method is characterized by multiplying by the output rate to convert it into a skew amount in UI units.

[0011] The differential skew generation method described in claim 3 of the present invention includes the step of oscillating and outputting a clock signal, The timing of the signal obtained by IQ modulating the aforementioned clock signal and adjusting the phase angle This includes a first IQ modulator 13A, a first pattern generation unit 14A, and a first control unit 15A. The steps include outputting a positive signal from the first output terminal 11A of the first signal generator 4A to the object under evaluation W, and connecting a terminator 5A to the second output terminal 12A of the first signal generator, The second signal generator 4B 3 The terminator 5B is connected to the output terminal 11B, and the timing of the signal obtained by IQ modulating the clock signal and adjusting the phase angle is obtained. This includes a second IQ modulator 13B, a second pattern generation unit 14B, and a second control unit 15B. The second signal generator 4 The step of outputting a negative signal to the object to be evaluated from the output terminal 12B, The transmission timing shift that synchronizes the first signal generator and the second signal generator and shifts the transmission timing of the signal by an integer unit of the UI of the set skew amount to distributes the fractional unit of the UI of the set skew amount to IQ modulation each allocate The steps, When the skew amount of the UI unit is set, the first control unit distributes the necessary IQ modulation amount and transmission timing shift amount and controls at least one of the first IQ modulator and the first pattern generation unit. such steps, and When the skew amount of the UI unit is set, the second control unit distributes it to the required IQ modulation amount and transmission timing shift amount, and the second IQ modulator and the second pattern generation unit performing at least one of the controls, characterized by including.

[0012] The differential skew generation method according to claim 4 of the present invention is the differential skew generation method according to claim 3, When the skew amount is set in units of time, the skew amount set in units of that time and is multiplied by the bit rate and converted into a skew amount in units of UI, characterized by this.

Advantages of the Invention

[0013] According to the present invention, positive and negative signals can be individually generated from two synchronized signal generators to vary the differential skew to a desired skew amount, improving convenience compared to the case of using a conventional mechanical delay adapter, and enabling measurements with excellent variable width, reproducibility, and resolution.

Brief Description of the Drawings

[0014] [Figure 1] It is a block diagram showing the internal configuration of a differential skew generation device according to the present invention.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings.

[0016] As shown in Figure 1, the differential skew generation device 1 of this embodiment generates differential skew, which is the time difference between a positive signal and a negative signal, which are mutually opposite-phase repeating signals input to the evaluation target W as two single-ended signals in a differential pair, with a desired amount of skew. It is generally configured to include a clock oscillator 2, a setting unit 3, a plurality of signal generators 4 (first signal generator 4A, second signal generator 4B), and a termination unit 5 (5A, 5B).

[0017] The differential skew generation device 1 operates a first signal generator 4A and a second signal generator 4B in synchronous operation, and manipulates the internal delay amount in each of the first and second signal generators 4B to input positive and negative signals, which have been varied to a desired skew amount, to the evaluation target W, thereby making the differential skew variable to a desired skew amount.

[0018] In Figure 1, the positive signal is denoted as Pos and the negative signal as Neg. Also, although Figure 1 shows the first signal generator 4A and the second signal generator 4B as separate block configurations, they can also be configured as a single module.

[0019] The clock oscillator 2 outputs a clock signal of the required frequency using either a square wave signal or a sine wave signal. The clock signal output from the clock oscillator 2 is input to the IQ modulator 13A of the first signal generator 4A (described later) and the IQ modulator 13B of the second signal generator 4B (described later), respectively.

[0020] The setting unit 3 is a GUI that the user inputs, and it sets the type of pattern (positive and negative signals) to be input to the evaluation target W, the bit rate, and the amount of skew for the first signal generator 4A and the second signal generator 4B, respectively, as information necessary to generate differential skew.

[0021] Here, the skew amount can be input in UI (unit interval) or time (sec). However, in this embodiment, as described later, the skew amount is varied by IQ modulation and transmission timing shift, so it operates in the dimension of phase ≈ UI rather than time (sec). Transmission timing shift means shifting the transmission timing of the signal bits (symbols in PAM3 and above) by an integer unit of the set skew amount UI: N bits (symbols). For this reason, when the setting unit 3 inputs and sets the skew amount in units of time (sec), the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B, described later, convert it to units of UI based on the formula UI = skew amount time (sec) × bit rate and set it.

[0022] In this embodiment, since the skew resolution is 2mUI units, depending on the input value in units of time (sec) set by the setting unit 3, it may not be in units of 2mUI and rounding may be necessary. In this case, the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B, as described later, calculate the time (sec) of the closest skew amount that can be achieved in units of 2mUI and perform a process to overwrite the input value set by the setting unit 3.

[0023] The signal generator 4 consists of a first signal generator 4A and a second signal generator 4B, both having the same configuration. The first signal generator 4A has a first output terminal 11A that outputs a positive signal and a second output terminal 12A that outputs a negative signal, and operates synchronously with the second signal generator 4B. As shown in Figure 1, it is configured with an IQ modulator 13A, a pattern generation unit 14A, and a control unit 15A, and a terminator 5A is connected to the second output terminal 12A.

[0024] The IQ modulator 13A, under the control of the control unit 15A, performs IQ modulation on the clock signal from the clock oscillator 2 based on the input of I and Q signals that are derived from the fractional units of the skew amount set in the setting unit 3.

[0025] The pattern generation unit 14A, under the control of the control unit 15A, generates positive and negative signals of a desired pattern based on the pattern type and bit rate set in the setting unit 3. The generated positive and negative signals are then shifted at the transmission timing based on an integer unit of the skew amount set in the setting unit 3, and the positive signal from the shifted signals is output from the first output terminal 11A.

[0026] The control unit 15A outputs a timing synchronization signal to the control unit 15B of the second signal generator 4B so that the first signal generator 4A operates in synchronous operation with the second signal generator 4B, and comprehensively controls the IQ modulator 13A and the pattern generation unit 14A.

[0027] Specifically, the control unit 15A outputs I and Q signals corresponding to the fractional units of the skew amount set by the setting unit 3 to the IQ modulator 13A, and adjusts and controls the phase angle of the clock signal from the clock oscillator 2. The control unit 15A also generates positive and negative signals of the desired pattern based on the pattern type and bit rate set by the setting unit 3, and controls the pattern generation unit 14A to perform a transmission timing shift based on the integer units of the skew amount set by the setting unit 3. Furthermore, when the skew amount is input and set in units of time (sec) by the setting unit 3, the control unit 15A converts and sets it in units of UI based on the formula UI = skew amount time (sec) × bit rate, and if rounding is necessary, calculates the closest skew amount time (sec) that can be achieved in 2mUI units and overwrites the input value from the setting unit 3.

[0028] The second signal generator 4B has the same configuration as the first signal generator 4A, and has a first output terminal 11B that outputs a positive signal and a second output terminal 12B that outputs a negative signal. It operates synchronously with the first signal generator 4A and, as shown in Figure 1, is configured with an IQ modulator 13B, a pattern generation unit 14B, and a control unit 15B, with a terminator 5B connected to the first output terminal 11B.

[0029] The IQ modulator 13B, under the control of the control unit 15B, performs IQ modulation on the clock signal from the clock oscillator 2 based on the input of I and Q signals that are derived from fractional units of the skew amount set in the setting unit 3.

[0030] The pattern generation unit 14B, under the control of the control unit 15B, generates positive and negative signals of a desired pattern based on the pattern type and bit rate set in the setting unit 3. The generated positive and negative signals are then shifted at the transmission timing based on an integer unit of the skew amount set in the setting unit 3, and the negative signal from the shifted signals is output from the second output terminal 12B.

[0031] The control unit 15B outputs a timing synchronization signal to the control unit 15A of the first signal generator 4A so that the second signal generator 4B operates in synchronous operation with the first signal generator 4A, and comprehensively controls the IQ modulator 13B and the pattern generation unit 14B.

[0032] Specifically, the control unit 15B outputs I and Q signals corresponding to the fractional units of the skew amount set by the setting unit 3 to the IQ modulator 13B, and adjusts and controls the phase angle of the clock signal from the clock oscillator 2. The control unit 15B also generates patterns (positive and negative signals) based on the pattern type and bit rate set by the setting unit 3, and controls the pattern generation unit 14B to perform a transmission timing shift based on the integer units of the skew amount set by the setting unit 3. Furthermore, when the skew amount is input and set in units of time (sec) by the setting unit 3, the control unit 15B converts and sets it in units of UI based on the formula UI = skew amount time (sec) × bit rate, and if rounding is necessary, calculates the closest skew amount time (sec) that can be achieved in 2mUI units and overwrites the input value from the setting unit 3.

[0033] The terminator 5 consists of a terminator 5A connected to an unused port of the first signal generator 4A and a terminator 5B connected to an unused port of the second signal generator 4B, preventing the signal output from being affected by total reflection at the open end of the output.

[0034] To explain further, terminator 5A is connected to the second output terminal 12A of the first signal generator 4A, which is an unused port, out of the two output terminals: the first output terminal 11A that outputs a positive signal and the second output terminal 12A that outputs a negative signal. Similarly, terminator 5B is connected to the first output terminal 11B of the second signal generator 4B, which is an unused port, out of the two output terminals: the first output terminal 11B that outputs a positive signal and the second output terminal 12B that outputs a negative signal.

[0035] Note that the termination device 5 is not limited to the connection configuration shown in Figure 1, and the connection configuration may be reversed. That is, termination device 5A may be connected to the first output terminal 11A of the pattern generation unit 14A of the first signal generator 4A, and termination device 5B may be connected to the second output terminal 12B of the pattern generation unit 14B of the second signal generator 4B. In this case, the negative signal output from the second output terminal 12A of the pattern generation unit 14A of the first signal generator 4A and the positive signal output from the first output terminal 11B of the pattern generation unit 14B of the second signal generator 4B are input to the device under evaluation W.

[0036] Next, we will explain how to vary the amount of skew using the differential skew generation device 1 configured as described above.

[0037] First, the setting unit 3 sets the type of pattern (positive signal, negative signal) to be input to the evaluation target W, the bitrate, and the skew amount for the first signal generator 4A and the second signal generator 4B, respectively.

[0038] Here, the skew amount can be input in UI or time (sec), but if the skew amount is set in units of time (sec), the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B convert it to units of UI based on the formula UI = skew amount in time (sec) × bit rate and set it.

[0039] Furthermore, if the input value in units of time (sec) set by the setting unit 3 does not result in a 2mUI unit and rounding is necessary, the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B calculate the closest skew amount in time (sec) that can be achieved in 2mUI units and overwrite the input value set by the setting unit 3.

[0040] Then, when the skew amount in UI units is set, the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B distribute the data to the required IQ modulation amount and transmission timing shift amount, and control the IQ modulators 13A, 13B and pattern generation units 14A, 14B.

[0041] Here, the transmission timing shift can only manipulate the skew amount in units of 1 UI, but the maximum range of change is large (e.g., ±64 UI). In contrast, IQ modulation allows for variable skew amounts in decimal units (e.g., 2 m UI), but the maximum range of change is small (±360° = ±1000 m UI). Therefore, in this embodiment, the integer units of the required skew amount (UI) are allocated to the transmission timing shift, and the decimal units are allocated to IQ modulation, and both are controlled.

[0042] To give specific numerical values, if the skew amount is 1250 (mUI), it corresponds to 1 transmission timing shift (1000 mUI) + 90° IQ modulation (250 mUI). Also, if the skew amount is -2250 (mUI), it corresponds to -3 transmission timing shifts (-3000 mUI) + 270° IQ modulation (750 mUI).

[0043] The examples above use IQ modulation from 0 to 360° (0 to 2π) = 0 to 1000 mUI, but the point at which the transmission timing shift is advanced is arbitrary. For example, IQ modulation can also be used with ±180° (±π) = 0 mUI as the center and ±500 mUI. In this case, if the skew amount is 1250 (mUI), it will be 1 transmission timing shift (1000 mUI) + IQ modulation 90° (250 mUI). Also, if the skew amount is -2250 (mUI), it will be -2 transmission timing shifts (-2000 mUI) + IQ modulation -90° (-250 mUI).

[0044] The examples above illustrate how the skew amount can be varied using both transmission timing shift and IQ modulation. However, depending on the set skew amount, it is also possible to vary the skew amount using at least one of the transmission timing shift and IQ modulation. For example, if the set skew amount is 1000 (mUI), it becomes a 1-degree transmission timing shift (1000mUI), and only the transmission timing shift is controlled. Also, if the set skew amount is 250 (mUI), it becomes a 90° IQ modulation (250mUI), and only the IQ modulation is controlled.

[0045] Incidentally, the pattern generation unit 14A of the first signal generator 4A and the pattern generation unit 14B of the second signal generator 4B are capable of generating PRBS patterns and arbitrary patterns, and the start timing of the patterns can be controlled. Specifically, for example, in order to achieve higher rate data output from a low-rate pattern generation unit, it can be configured with an FPGA that outputs 1 / N data and multiple MUXs (N:1 MUX for MSB output, N:1 MUX for LSB output, 2:1 MUX for PAM4 output), or it can be configured with D-FFs, but it is not limited to these circuit configurations.

[0046] Thus, according to this embodiment, positive and negative signals can be individually generated from two synchronized signal generators (first signal generator 4A and second signal generator 4B), allowing the differential skew to be varied to a desired amount. This not only improves convenience compared to using a conventional mechanical delay adapter, but also enables variable skew with superior variable range, reproducibility, and resolution. Specifically, it achieves a variable range of ±64 UI and a resolution of 2 m UI, and with an operating rate of 2.4 Gbaud to 64.2 Gbaud, converting this to time units results in a maximum variable range of ±26.6 ns and a minimum resolution of 31.1 fs.

[0047] Incidentally, the differential skew generation device 1 of this embodiment is not configured to generate positive and negative signals from a single signal generator, but rather, as shown in Figure 1, it is configured to generate positive and negative signals individually from two synchronously operating signal generators (first signal generator 4A and second signal generator 4B). Therefore, each signal can be manipulated independently for parameters other than skew. The manipulable parameters depend on the functions of the signal generators, and examples include amplitude, Tx equalizer (emphasis), and PAM linearity.

[0048] Furthermore, according to this embodiment, since it does not affect the transmission line characteristics and is not affected by reflections from the object being measured, the evaluator can easily isolate and evaluate only the effects of skew.

[0049] Furthermore, because positive and negative signals can be manipulated independently, it is possible to intentionally disrupt the symmetry of the waveform, enabling skew evaluation not only from the perspective of arrival timing, but also from the perspective of waveform asymmetry.

[0050] Furthermore, even if there is reflection from the object being evaluated, the differential coupling on the signal generator side will prevent it from affecting the output, making it easier for the evaluator to isolate the effects of skew.

[0051] Furthermore, by allowing users to input the amount of skew in time units or UI units in the setting unit 3, or by enabling intuitive operation of the setting unit 3 while a waveform image with skew is displayed, it becomes easier for users to intuitively understand what kind of skewed signal they are applying.

[0052] The best mode of the differential skew generation apparatus and differential skew generation method according to the present invention has been described above, but the present invention is not limited by this description and drawings. That is, other modes, examples, and operational techniques based on this embodiment, as made by those skilled in the art, are all included in the scope of the present invention. [Explanation of Symbols]

[0053] 1. Differential Skew Generation Device 2 Clock oscillators 3. Settings section 4. Signal Generator 4A First signal generator 4B Second signal generator 5(5A,5B) Terminator 11A, 11B First output terminal 12A, 12B Second output terminal 13A, 13B IQ modulator 14A, 14B Pattern generation unit 15A, 15B Control Unit W (Evaluation Target)

Claims

1. A clock oscillator (2) that outputs a clock signal, The first signal generator (4A) includes a first output terminal (11A) that outputs a positive signal to the object to be evaluated (W) at the timing of a signal obtained by IQ modulating the clock signal and adjusting the phase angle, and a second output terminal (12A) to which a terminator (5A) is connected, and a first IQ modulator (13A), a first pattern generation unit (14A), and a first control unit (15A), It has a third output terminal (11B) to which a terminator (5B) is connected, and a fourth output terminal (12B) that outputs a negative signal to the evaluation target at the timing of a signal obtained by IQ modulating the clock signal and adjusting the phase angle, and also includes a second signal generator (4B) which includes a second IQ modulator (13B), a second pattern generation unit (14B), and a second control unit (15B), The first signal generator and the second signal generator operate synchronously, and allocate the signal transmission timing shift by an integer unit of the set skew amount UI to IQ modulation, and the fractional unit of the set skew amount UI to IQ modulation. When the skew amount in units of UI is set, the first control unit distributes the required IQ modulation amount and transmission timing shift amount and controls at least one of the first IQ modulator and the first pattern generation unit. A differential skew generation device characterized in that, when a skew amount in units of UI is set, the second control unit distributes the required IQ modulation amount and transmission timing shift amount to control at least one of the second IQ modulator and the second pattern generation unit.

2. The differential skew generation device according to claim 1, characterized in that when the skew amount is set in units of time, the skew amount set in units of time is multiplied by the bitrate to convert it into a skew amount in units of UI.

3. The steps include: generating an oscillator output of the clock signal, The steps include: outputting a positive signal from the first output terminal (11A) of the first signal generator (4A), which includes a first IQ modulator (13A), a first pattern generation unit (14A), and a first control unit (15A), to the evaluation target (W) based on the timing of the signal obtained by IQ modulating the clock signal and adjusting the phase angle, and connecting a terminator (5A) to the second output terminal (12A) of the first signal generator; The steps include: connecting a terminator (5B) to the third output terminal (11B) of the second signal generator (4B), and outputting a negative signal to the evaluation target from the fourth output terminal (12B) of the second signal generator, which includes a second IQ modulator (13B), a second pattern generation unit (14B), and a second control unit (15B), based on the timing of the signal obtained by IQ modulating the clock signal and adjusting the phase angle; The first signal generator and the second signal generator are operated synchronously, and the transmission timing of the signal is shifted by an integer unit of the set skew amount UI, and a fractional unit of the set skew amount UI is allocated to IQ modulation. When the skew amount in the unit of UI is set, the first control unit distributes the necessary IQ modulation amount and transmission timing shift amount and controls at least one of the first IQ modulator and the first pattern generation unit; A differential skew generation method characterized by including the step of, when a skew amount in units of UI is set, the second control unit distributes the data to the required IQ modulation amount and transmission timing shift amount and controls at least one of the second IQ modulator and the second pattern generation unit.

4. The differential skew generation method according to claim 3, characterized in that when the skew amount is set in units of time, the skew amount set in units of time is multiplied by the bitrate to convert it into a skew amount in units of UI.

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