JP7818188B2 - Differential skew generating device and differential skew generating method - Google Patents

Description

The present invention relates to a differential skew generating device and a differential skew generating method that generate differential skew, which is the time difference between a positive signal and a negative signal.

Differential transmission has excellent resistance to common-mode noise, so it is used in many high-speed serial communications that require high waveform quality. Because differential transmission assumes that the arrival timing of the positive and negative signals is equal, if the timing difference (skew) is not small enough, it cannot be effective and may actually have a negative effect.

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 skew and distortion and reflections in the signals, significantly degrading waveform quality.

In recent years, high-speed serial communications have seen the use of 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, making it increasingly important to evaluate the impact of skew on transmission paths and devices.

By the way, one known technology for monitoring the above-mentioned skew is one that uses a divider, as disclosed in Patent Document 1 below.

Patent No. 6890625

However, monitoring skew requires inserting a divider or Pickoff-Tee, as disclosed in Patent Document 1, into the signal path and monitoring the branched signal, which poses problems such as degradation of signal quality due to the insertion of the divider or Pickoff-Tee, and the inclusion of insertion loss. To solve this problem, a common monitoring method that does not include loss involves reconnecting the device under test to the oscilloscope each time. However, this complicates the measurement procedure and makes it impossible to simultaneously observe the behavior of the measuring instrument and the waveform, significantly reducing the efficiency of debugging the device under test, etc.

The present invention was made in consideration of the above problems, and aims to provide a differential skew generating device and method that can adjust the differential skew to the desired skew amount without mechanical manipulation and that allows waveform observation.

In order to achieve the above object, a differential skew generating device according to a first aspect of the present invention comprises: a clock oscillator 2 for oscillating and outputting a clock signal;
a first signal generator 4A having a first output terminal 11A for outputting a positive signal and a second output terminal 12A for outputting a negative signal, the first signal generator 4A including a first IQ modulator 13A for outputting the positive signal from the first output terminal to the device under test W at the timing of a signal obtained by IQ-modulating the clock signal to adjust the phase angle, a first pattern generating unit 14A, and a first control unit 15A ;
a second signal generator (4B) having a third output terminal (11B) for outputting a positive signal and a fourth output terminal (12B) for outputting a negative signal, the second signal generator ( 4B ) including a second IQ modulator (13B), a second pattern generating unit (14B), and a second control unit (15B) for outputting the negative signal from the fourth output terminal to the device under test at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle;
a monitor device 5 connected to the second output terminal of the first signal generator and the third output terminal of the second signal generator;
the first signal generator and the second signal generator operate synchronously, and allocate a fractional unit of UI of the set skew amount to IQ modulation, and allocate a transmission timing shift that shifts the transmission timing of the signal by an integer unit of UI of the set skew amount , respectively ;
the first control unit, when a skew amount in units of UI is set, controls at least one of the first IQ modulator and the first pattern generation unit by dividing the amount into a required IQ modulation amount and a required transmission timing shift amount;
The second control unit is characterized in that, when a skew amount in units of UI is set, it allocates 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 .

A differential skew generator according to claim 2 of the present invention is the differential skew generator according to claim 1, 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.

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 the positive signal from the first output terminal to the device under test W at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle in a first signal generator 4A having a first output terminal 11A for outputting a positive signal and a second output terminal 12A for outputting a negative signal, and including a first IQ modulator 13A, a first pattern generating unit 14A, and a first control unit 15A;
a step of outputting the negative signal from the fourth output terminal to the device under test at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle in a second signal generator (4B) having a third output terminal (11B) for outputting a positive signal and a fourth output terminal (12B) for outputting a negative signal, and including a second IQ modulator (13B), a second pattern generating unit (14B), and a second control unit (15B);
connecting the second output terminal of the first signal generator and the third output terminal of the second signal generator to a monitor device (5);
a step of synchronously operating the first signal generator and the second signal generator, and allocating a fractional unit of UI of the set skew amount to IQ modulation for a transmission timing shift that shifts the signal transmission timing by an integer unit of UI of the set skew amount ;
When the skew amount in units of UI is set, the first control unit controls at least one of the first IQ modulator and the first pattern generation unit by dividing the amount into a required IQ modulation amount and a required transmission timing shift amount;
When the skew amount in units of UI is set, the second control unit divides the necessary IQ modulation amount and transmission timing shift amount into control of at least one of the second IQ modulator and the second pattern generation unit .

A 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.

According to the present invention, by generating positive and negative signals separately from two signal generators, it is possible to vary the amount of differential skew with excellent variable width and resolution without mechanical operation, and it is also possible to simultaneously observe the waveforms without modifying the paths through which the positive and negative signals are input to the device under test.

1 is a block diagram showing the internal configuration of a differential skew generator according to the present invention;

The following describes in detail the embodiments of the present invention, with reference to the accompanying drawings.

As shown in FIG. 1, the differential skew generating device 1 of this embodiment generates differential skew, which is the time difference between a positive signal and a negative signal, which are repetitive signals of opposite phases that are input to the device under test W as two single-ended signals in a differential pair. It 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 monitor device 5.

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 positive and negative signals that have been adjusted to the desired skew amount to the device under test W, making it possible to adjust the differential skew to the desired skew amount and observe the waveform.

Note that in Figure 1, positive signals are represented as Pos and negative signals as Neg. Also, in Figure 1, the first signal generator 4A and second signal generator 4B are shown as separate block configurations, but they can also be configured as a single module.

The clock oscillator 2 oscillates and outputs a clock signal of the required frequency using a rectangular 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 below) of the first signal generator 4A and an IQ modulator 13B (described below) of the second signal generator 4B.

The setting unit 3 is a GUI operated by the user to input information necessary to generate differential skew, such as the type of pattern (positive signal and negative signal) to be input to the device under test W, the bit rate, and the amount of skew for each of the first signal generator 4A and second signal generator 4B to obtain differential skew.

Here, the skew amount can be input in UI (unit interval) or time (sec). However, in this embodiment, as with the skew amount varying method described below, the skew amount is varied using 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 the signal bits (symbols in PAM3 and higher) by an integer unit of UI of the set skew amount: N bits (symbols). Therefore, when the skew amount is input and set by the setting unit 3 in units of time (sec), the setting is converted to units of UI using the formula UI = skew amount time (sec) × bit rate 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.

In this embodiment, since the skew resolution is in 2mUI units, depending on the input value in units of time (sec) input and set by the setting unit 3, it may not be in 2mUI units 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 (described below) calculate the closest skew amount time (sec) that can be achieved in 2mUI units and perform a process of overwriting the input value by the setting unit 3.

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 FIG. 1, it is configured with an IQ modulator 13A, a pattern generation unit 14A, and a control unit 15A, and the second output terminal 12A is connected to the monitor device 5.

Under the control of the control unit 15A, 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, the pattern generation unit 14A generates positive and negative signals of the desired pattern based on the pattern type 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 transmission timing-shifted positive signal from the first output terminal 11A and the transmission timing-shifted negative signal from the second output terminal 12A.

The control unit 15A outputs a timing synchronization signal to the control unit 15B (described later) 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 pattern generation unit 14A in an integrated manner.

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 pattern type and bit rate set by the setting unit 3, and controls the pattern generation unit 14A to shift the transmission timing 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 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 and sets the value input by the setting unit 3.

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 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 its first output terminal 11B is connected to the monitor device 5.

Under the control of the control unit 15B, 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, the pattern generation unit 14B generates positive and negative signals of the desired pattern based on the pattern type 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 transmission timing-shifted positive signal from the first output terminal 11B and the transmission timing-shifted negative signal from the second output terminal 12B.

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 pattern generation unit 14B in an integrated manner.

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 pattern type and bit rate set by the setting unit 3, and controls the pattern generation unit 14B to shift the transmission timing based on the integer unit 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) x bit rate, and if rounding is necessary, calculates the closest skew amount time (sec) that can be achieved in 2mUI units, and overwrites and sets the value input by the setting unit 3.

The monitor device 5 is a monitoring device for observing the waveforms of the patterns (positive and negative signals) generated by the first signal generator 4A and the second signal generator 4B, and is connected to the free ports of the output terminals of the first signal generator 4A and the second signal generator 4B, i.e., the second output terminal 12A of the first signal generator 4A and the first output terminal 11B of the second signal generator 4B.

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

In addition, the cables, differential lines, etc. used in the monitor device 5 have characteristics that are as similar as possible to the cables, differential lines, etc. used between the first signal generator 4A and the device under test W, and between the second signal generator 4B and the device under test W, so as to enable more accurate waveform observation.

Next, we will explain how to vary the amount of skew using the differential skew generator 1 configured as described above.

First, the setting unit 3 is used to set the type of pattern (positive signal, negative signal) to be input to the device under test W, the bit rate, and the amount of skew for each of the first signal generator 4A and second signal generator 4B.

Here, the skew amount can be input in UI or time (sec). However, 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) x bit rate.

In addition, if the input value in units of time (sec) input and set by the setting unit 3 does not match 2mUI units and requires rounding, 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 of time (sec) that can be achieved in 2mUI units, and overwrite the input value by the setting unit 3.

Then, once 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 required IQ modulation amount and transmission timing shift amount and control the IQ modulators 13A, 13B and pattern generation units 14A, 14B.

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

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

The above examples use IQ modulation at 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 at ±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).

Note that while the above examples show cases where the skew amount is varied using both transmission timing shift and IQ modulation, it is also possible to vary the skew amount using either transmission timing shift or IQ modulation, depending on the amount of skew that is set. For example, if the amount of skew that is set is 1000 (mUI), the result is 1 transmission timing shift (1000 mUI), and only the transmission timing shift is controlled. Furthermore, if the amount of skew that is set is 250 (mUI), the result is 90° IQ modulation (250 mUI), and only the IQ modulation is controlled.

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 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, 2:1 MUX for PAM4 output), or they can be configured with D-FFs, but are not limited to these circuit configurations.

As such, according to this embodiment, by generating positive and negative signals separately from two signal generators (first signal generator 4A and second signal generator 4B), it is possible to vary the amount of differential skew with excellent variable width and resolution without mechanical operation. Specifically, a variable width of ±64 UI and a resolution of 2 mUI are achieved. The module's operating rate is 2.4 Gbaud to 64.2 Gbaud, which, when converted to time units, translates to a maximum variable width of ±26.6 ns and a minimum resolution of 31.1 fs.

Furthermore, as shown in FIG. 1, the device under test W is connected to one of the two outputs (first output terminals 11A and 11B, second output terminals 12A and 12B) of the first signal generator 4A and the second signal generator 4B (in the example of FIG. 1, the first output terminal 11A and the second output terminal 12B), and the other output (in the example of FIG. 1, the first output terminal 11B and the second output terminal 12A) is connected to the monitor device 5 and used for monitoring, so waveform observation is possible at the same time without modifying the main path (the path that inputs positive and negative signals to the device under test W).

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 FIG. 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 parameters that can be manipulated depend on the functions of the signal generator, but examples include amplitude, Tx equalizer (emphasis), and PAM linearity.

One method for evaluating the input signal to the device under test is to insert a divider or Pickoff-Tee into the signal path, but in this case, it is necessary to accept the degradation of signal quality caused by the insertion of the divider or Pickoff-Tee.

In addition, dividers and Pickoff-Tees generally have an insertion loss of around 14 dB or 20 dB, so the measuring instrument must have high S/N performance. If this is not acceptable, one method is to reconnect the DUT to the oscilloscope each time, but in this case, it is not possible to observe the behavior of the measuring instrument and the waveform simultaneously.

In contrast, this embodiment can provide an evaluation environment that achieves both. Furthermore, even if there is reflection from the device under test, there is no risk of the output being affected by differential coupling on the signal generator side, making it easy for the evaluator to isolate the effects of skew. Furthermore, by using the other output for monitoring, as shown in Figure 1, it is possible to monitor the waveform and skew input to the device under test without inserting a divider or Pickoff-Tee into the signal path.

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. This makes it easier for the user to intuitively grasp the type of skewed signal they are providing, and by comparing the displayed waveform image with the monitored waveform image, it becomes possible to confirm whether the intended skew has been added.

The above describes the best mode for the differential skew generating device and differential skew generating method according to the present invention, but 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 are developed by those skilled in the art based on this mode are naturally included within the scope of the present invention.

REFERENCE SIGNS LIST 1 differential skew generating device 2 clock oscillator 3 setting section 4 signal generator 4A first signal generator 4B second signal generator 5 monitor device 11A, 11B first output terminal 12A, 12B second output terminal 13A, 13B IQ modulator 14A, 14B pattern generating section 15A, 15B control section W device under test

Claims (4)

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 and a second output terminal (12A) for outputting a negative signal, the first signal generator including a first IQ modulator (13A), a first pattern generating unit (14A), and a first control unit (15A) for outputting the positive signal from the first output terminal to a device under test (W) at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle;
a second signal generator (4B) having a third output terminal (11B) for outputting a positive signal and a fourth output terminal (12B) for outputting a negative signal, the second signal generator including a second IQ modulator (13B), a second pattern generating unit (14B), and a second control unit (15B) for outputting the negative signal from the fourth output terminal to the device under test at the timing of a signal obtained by IQ-modulating the clock signal and adjusting its phase angle;
a monitor device (5) connected to the second output terminal of the first signal generator and the third output terminal of the second signal generator;
the first signal generator and the second signal generator operate synchronously, and allocate a fractional unit of UI of the set skew amount to IQ modulation, and allocate a transmission timing shift that shifts the transmission timing of the signal by an integer unit of UI of the set skew amount, respectively;
the first control unit, when a skew amount in units of UI is set, controls at least one of the first IQ modulator and the first pattern generation unit by dividing the amount into a required IQ modulation amount and a required transmission timing shift amount;
A differential skew generating device characterized in that, when a skew amount in UI units is set, the second control unit controls at least one of the second IQ modulator and the second pattern generation unit by allocating the required IQ modulation amount and transmission timing shift amount. 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 a bit rate to convert it into a skew amount in units of UI. oscillating and outputting a clock signal;
a step of outputting the positive signal from the first output terminal to a device under test (W) at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle in a first signal generator (4A) having a first output terminal (11A) for outputting a positive signal and a second output terminal (12A) for outputting a negative signal, and including a first IQ modulator (13A), a first pattern generating unit (14A), and a first control unit (15A);
a step of outputting the negative signal from the fourth output terminal to the device under test at the timing of a signal obtained by IQ-modulating the clock signal and adjusting the phase angle in a second signal generator (4B) having a third output terminal (11B) for outputting a positive signal and a fourth output terminal (12B) for outputting a negative signal, and including a second IQ modulator (13B), a second pattern generating unit (14B), and a second control unit (15B);
connecting the second output terminal of the first signal generator and the third output terminal of the second signal generator to a monitoring device (5);
a step of synchronously operating the first signal generator and the second signal generator, and allocating a fractional unit of UI of the set skew amount to IQ modulation for a transmission timing shift that shifts the signal transmission timing by an integer unit of UI of the set skew amount;
When the skew amount in units of UI is set, the first control unit controls at least one of the first IQ modulator and the first pattern generation unit by dividing the amount into a required IQ modulation amount and a required transmission timing shift amount;
a step of controlling at least one of the second IQ modulator and the second pattern generation unit by the second control unit when a skew amount in UI units is set, by dividing the amount into a required IQ modulation amount and a required transmission timing shift amount. 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 a bit rate to convert it into a skew amount in units of UI.