Differential skew generation device 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 generating device and a differential skew generating method for generating a differential skew, which is the time difference between a positive signal and a negative signal input to an object to be evaluated. [Background technology]

[0002] Differential transmission has excellent resistance to common-mode noise, and is therefore used in many high-speed serial communications that require high waveform quality. Because differential transmission is based on the premise that the arrival timing of the positive and negative signals is equal, if the timing difference (skew) is not sufficiently small, the effectiveness of differential transmission cannot be realized and may even have a negative effect.

[0003] In particular, when differential signals pass through differential lines, capacitive, inductive, or a combination of these couplings occurs between the positive and negative signals, causing distortion and reflection in the signals due to skew, significantly degrading waveform quality.

[0004] In recent years, high-speed serial communications have been using faster modulation rates and multi-level modulation technology; for example, PCIe Gen6 uses the 32 Gbaud PAM4 modulation method. Accordingly, requirements for waveform quality have become more stringent, and evaluation of the impact of skew on transmission paths and devices has become increasingly important. Patent Document 1 below discloses a technology related to skew adjustment.

[0005] Incidentally, one method for evaluating the above-mentioned skew is to use a mechanical delay adapter, which is a device that mechanically varies the line length of a coaxial line. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-096760 Summary of the Invention [Problem to be solved by the invention]

[0007] However, because mechanical delay adapters are operated mechanically, they have limitations in repeatability, resolution, and variable range, making them unsuitable for automation. While there are types with wider variable ranges, these involve a trade-off with resolution, making it difficult to achieve both variable range and resolution. Furthermore, simply inserting a mechanical delay adapter affects transmission characteristics, so the tester must carefully examine the measurement results to determine whether the effect is due to the mechanical delay adapter or skew. While the effects of the frequency characteristics and insertion loss of a 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, making it difficult to maintain precise phase calibration. Coupling and reflections that occur on the line are often determined by the line length (phase), and this changes depending on the operation, making it difficult to isolate the effects of skew.

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

[0009] In order to achieve the above object, a differential skew generating device according to claim 1 of the present invention comprises: a clock oscillator 2 that oscillates and outputs a clock signal; a first signal generator (4A) having a first output terminal (11A) that outputs a positive signal to an 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; a second signal generator (4B) having a first output terminal (11B) to which a terminator (5B) is connected, and a second output terminal (12B) for outputting a negative signal to the object to be evaluated at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle; The first signal generator and the second signal generator operate synchronously and are characterized by controlling a transmission timing shift that shifts the signal transmission timing by an integer unit of UI of the set skew amount, and allocating a decimal unit of UI of the set skew amount as IQ modulation.

[0010] The differential skew generator according to claim 2 of the present invention is the differential skew generator according to claim 1, When the amount of skew is set in units of time, the amount of skew set in units of time is multiplied by the bit rate and converted into the amount of skew in units of UI.

[0011] A differential skew generating method according to claim 3 of the present invention comprises the steps of: oscillating and outputting a clock signal; a step of outputting a positive signal from a first output terminal 11A of a first signal generator 4A to an object to be evaluated W at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle, and connecting a terminator 5A to a second output terminal 12A of the first signal generator; connecting a terminator 5B to a first output terminal 11B of a second signal generator 4B, and outputting a negative signal from a second output terminal 12B of the second signal generator to the object to be evaluated at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle; a transmission timing shift step of synchronously operating the first signal generator and the second signal generator and shifting the signal transmission timing by an integer unit of UI of the set skew amount, and a step of allocating and controlling a decimal unit of UI of the set skew amount as IQ modulation.

[0012] The differential skew generation method according to claim 4 of the present invention is the differential skew generation method according to claim 3, further comprising: When the amount of skew is set in units of time, the amount of skew set in units of time is multiplied by the bit rate and converted into the amount of skew in units of UI. [Effects of the Invention]

[0013] According to the present invention, positive and negative signals can be generated individually from two synchronized signal generators, allowing the differential skew to be adjusted to the desired skew amount. This not only improves convenience compared to the use of conventional mechanical delay adapters, but also enables measurements with excellent variable width, reproducibility, and resolution. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing the internal configuration of a differential skew generator according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] As shown in FIG. 1, the differential skew generating device 1 of this embodiment generates a differential skew, which is the time difference between a positive signal and a negative signal, which are repetitive signals of opposite phases and input to an evaluation object W as two single-ended signals in a differential pair, with a desired amount of skew, and is generally configured with a clock oscillator 2, a setting unit 3, multiple signal generators 4 (a first signal generator 4A, a second signal generator 4B), and a terminator 5 (5A, 5B).

[0017] The differential skew generating device 1 synchronizes the operation of the first signal generator 4A and the second signal generator 4B, manipulates the internal delay amount in each of the first signal generator 4A and the second signal generator 4B, and inputs a positive signal and a negative signal that have been varied to the desired skew amount to the evaluation object W, thereby making it possible to vary the differential skew to the desired skew amount.

[0018] In Fig. 1, a positive signal is represented as Pos and a negative signal as Neg. Also, in Fig. 1, the first signal generator 4A and the second signal generator 4B are illustrated as separate blocks, but they can also be configured as a single module.

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

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

[0021] Here, the skew amount can be input in UI (unit interval) or time (sec). However, in this embodiment, as in the skew amount varying method described below, 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). Note that transmission timing shift means shifting the transmission timing of signal bits (symbols in PAM3 or higher) by an integer unit of UI of the skew amount to be set: N bits (symbols). Therefore, when the skew amount is input and set by the setting unit 3 in units of time (sec), the skew amount is converted into UI units in the control unit 15A (described later) of the first signal generator 4A and the control unit 15B (described later) of the second signal generator 4B, based on the formula UI = skew amount time (sec) × bit rate, and set.

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

[0023] The signal generator 4 is composed of a first signal generator 4A and a second signal generator 4B, each 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 in synchronization with the second signal generator 4B. As shown in Fig. 1, the first signal generator 4A is composed of 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 performs IQ modulation on the clock signal from the clock oscillator 2 using the input I and Q signals based on the decimal unit of the skew amount set by the setting unit 3 under the control of the control unit 15A.

[0025] Under the control of the control unit 15A, the pattern generation unit 14A generates positive and negative signals of the desired pattern based on the type of pattern and bit rate set by the setting unit 3, shifts the transmission timing of the generated positive and negative signals based on the integer unit of the skew amount set by the setting unit 3, and outputs the positive signals of the transmission timing shifted signals 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 synchronization with the second signal generator 4B, and controls the IQ modulator 13A and the pattern generation unit 14A in an integrated manner.

[0027] Specifically, the control unit 15A outputs I and Q signals corresponding to the decimal unit 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 a desired pattern based on the type of pattern 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 unit of the skew amount set by the setting unit 3. Furthermore, when the skew amount is input and set by the setting unit 3 in units of time (sec), the control unit 15A converts it into 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 performs processing to overwrite and set the value input by 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. The second signal generator 4B operates in synchronization with the first signal generator 4A, and as shown in FIG. 1, is configured with an IQ modulator 13B, a pattern generation unit 14B, and a control unit 15B, and a terminator 5B is connected to the first output terminal 11B.

[0029] The IQ modulator 13B performs IQ modulation on the clock signal from the clock oscillator 2 using the input I and Q signals based on the decimal unit of the skew amount set by the setting unit 3 under the control of the control unit 15B.

[0030] Under the control of the control unit 15B, the pattern generation unit 14B generates positive and negative signals of the desired pattern based on the type of pattern and bit rate set by the setting unit 3, shifts the transmission timing of the generated positive and negative signals based on the integer unit of the skew amount set by the setting unit 3, and outputs the negative signals of the transmission timing shifted signals 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 synchronization with the first signal generator 4A, and controls the IQ modulator 13B and the pattern generation unit 14B in an integrated manner.

[0032] Specifically, the control unit 15B outputs I and Q signals corresponding to the decimal unit 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 type of pattern 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 unit of the skew amount set by the setting unit 3. Furthermore, when the skew amount is input and set by the setting unit 3 in units of time (sec), the control unit 15B converts it into 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 performs processing to overwrite and set the value input by the setting unit 3.

[0033] The terminators 5 consist of terminators 5A connected to the free port of the first signal generator 4A and terminators 5B connected to the free port of the second signal generator 4B, and prevent the signal output from being affected by total reflection at the open end of the output.

[0034] More specifically, of the two output terminals of the first signal generator 4A, a first output terminal 11A for outputting a positive signal and a second output terminal 12A for outputting a negative signal, terminator 5A is connected to the second output terminal 12A, which is an unused port. Also, of the two output terminals of the second signal generator 4B, a first output terminal 11B for outputting a positive signal and a second output terminal 12B for outputting a negative signal, terminator 5B is connected to the first output terminal 11B, which is an unused port.

[0035] The connection configuration of the terminator 5 is not limited to that shown in Figure 1, and the connection configuration may be reversed. That is, the terminator 5A may be connected to the first output terminal 11A of the pattern generation unit 14A of the first signal generator 4A, and the terminator 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 evaluation object W.

[0036] Next, a method for varying the amount of skew using the differential skew generator 1 configured as above will be described.

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

[0038] Here, the skew amount can be input in UI or time (sec). If the skew amount is input and 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 into UI units and set it based on the formula UI = skew amount time (sec) × bit rate.

[0039] Furthermore, if the input value in units of time (sec) input and set by the setting unit 3 does not match 2 mUI units and rounding is required, the control unit 15A of the first signal generator 4A and the control unit 15B of the second signal generator 4B calculate the time (sec) of the closest skew amount that can be achieved in 2 mUI units, and perform a process of overwriting the input value 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 allocate the necessary IQ modulation amount and transmission timing shift amount to control the IQ modulators 13A and 13B and the pattern generation units 14A and 14B.

[0041] Here, transmission timing shift can only manipulate the amount of skew in 1 UI increments, but the maximum variation is large (for example, ±64 UI). In contrast, IQ modulation can vary the amount of skew in decimal units (for example, 2 mUI), but the maximum variation is small (±360° = ±1000 mUI). For this reason, in this embodiment, the integer unit portion of the required skew amount (UI) is allocated to transmission timing shift, and the decimal unit portion is allocated to IQ modulation, and both are controlled.

[0042] Specifically, when the skew amount is 1250 (mUI), it is 1 transmission timing shift (1000 mUI) + IQ modulation 90° (250 mUI), and when the skew amount is -2250 (mUI), it is -3 transmission timing shift (-3000 mUI) + IQ modulation 270° (750 mUI).

[0043] In the above examples, IQ modulation is used in the range of 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 be used in the range of ±500 mUI with ±180° (±π) = 0 mUI as the center. In this case, if the skew amount is 1250 (mUI), the result is 1 transmission timing shift (1000 mUI) + IQ modulation 90° (250 mUI). Also, if the skew amount is -2250 (mUI), the result is -2 transmission timing shift (-2000 mUI) + IQ modulation -90° (-250 mUI).

[0044] In the above examples, the skew amount is varied by both transmission timing shift and IQ modulation, but depending on the set skew amount, it is also possible to vary the skew amount by at least one of transmission timing shift and IQ modulation. For example, if the set skew amount is 1000 (mUI), the result is 1 transmission timing shift (1000mUI), and only the transmission timing shift is controlled. Also, if the set skew amount is 250 (mUI), the result is IQ modulation 90° (250mUI), and only the IQ modulation is controlled.

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

[0046] As described above, according to this embodiment, the differential skew can be varied to a desired skew amount by individually generating positive and negative signals from two synchronized signal generators (first signal generator 4A and second signal generator 4B), which not only improves convenience compared to the use of conventional mechanical delay adapters, but also enables skew variation with excellent variable width, reproducibility, and resolution. Specifically, a variable width of ±64 UI and a resolution of 2 mUI are achieved, and the operating rate is 2.4 Gbaud to 64.2 Gbaud. Converting this to time units results in a maximum variable width of ±26.6 ns and a minimum resolution of 31.1 fs.

[0047] The differential skew generator 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, is configured to generate positive and negative signals individually from two synchronously operating signal generators (first signal generator 4A and second signal generator 4B). This allows each signal to be independently manipulated for parameters other than skew. The manipulable parameters depend on the functions of the signal generators, but examples include amplitude, Tx equalizer (emphasis), and PAM linearity.

[0048] Furthermore, according to this embodiment, since there is no effect on the transmission line characteristics and no effect of reflection from the device under test, the evaluator can easily separate and evaluate only the effect of skew.

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

[0050] Furthermore, even if there is a reflection from the evaluation target, there is no risk of it affecting the output due to differential coupling on the signal generator side, making it easy for the evaluator to separate the effects of skew.

[0051] Furthermore, the amount of skew can be controlled by inputting it in time units or UI units in the setting unit 3, or by intuitively operating the setting unit 3 while a skewed waveform image is displayed, making it easier for the user to intuitively grasp what kind of skewed signal is being provided.

[0052] While the best mode for the differential skew generating device and method according to the present invention has been described above, the present invention is not limited to the description and drawings of this mode. In other words, all other modes, embodiments, and operational techniques that can be realized by those skilled in the art based on this mode are naturally included in the scope of the present invention. [Explanation of symbols]

[0053] 1. Differential skew generator 2 Clock oscillator 3. Settings 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 section 15A, 15B control section W Evaluation Target

Claims

1. a clock oscillator (2) that oscillates and outputs a clock signal; a first signal generator (4A) having a first output terminal (11A) for outputting a positive signal to an evaluation object (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; a second signal generator (4B) having a first output terminal (11B) to which a terminator (5B) is connected, and a second output terminal (12B) for outputting a negative signal to the evaluation object at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle, The first signal generator and the second signal generator operate synchronously, and perform a transmission timing shift that shifts the signal transmission timing by an integer unit of UI of the set skew amount, or control at least one of them by allocating a fractional unit of UI of the set skew amount to IQ modulation.

2. 2. The differential skew generating device according to claim 1, wherein when the skew amount is set in units of time, the skew amount set in units of time is multiplied by the bit rate to convert it into a skew amount in units of UI.

3. oscillating and outputting a clock signal; a step of outputting a positive signal from a first output terminal (11A) of a first signal generator (4A) to an evaluation object (W) at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle, and connecting a terminator (5A) to a second output terminal (12A) of the first signal generator; a step of connecting a terminator (5B) to a first output terminal (11B) of a second signal generator (4B), and outputting a negative signal from a second output terminal (12B) of the second signal generator to the evaluation object at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle; a transmission timing shift step of synchronously operating the first signal generator and the second signal generator and shifting the signal transmission timing by an integer unit of UI of a set skew amount, and allocating a fractional unit of UI of the set skew amount to IQ modulation and controlling at least one of them.

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

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