JP6672375B2 - Error rate measuring device and eye margin measuring method of the device - Google Patents

Description

  The present invention relates to an error rate measuring apparatus that transmits a test signal of a known pattern to a device under test (DUT: Device Under Test), receives an output from the device under test accompanying the transmission of the test signal, and measures a bit error rate. And an eye margin measuring method of the apparatus.

  2. Description of the Related Art With the increase in the number of users and the spread of multimedia communication, various types of digital communication devices are required to have higher transmission capacity. A bit error rate (hereinafter, referred to as BER) is one of the indexes for evaluating the quality of a digital signal in this type of digital communication apparatus. The BER is defined as a comparison between the number of occurrences of code errors in the received data and the total number of received data, and is measured by, for example, an error rate measurement device disclosed in Patent Document 1 below.

  Conventionally, this type of error rate measuring apparatus is divided into a transmitting side and a receiving side, transmits a known pattern signal from the transmitting side to a device under test (DUT), and transmits the pattern under test (DUT) with the transmission of the pattern signal. The BER is measured by receiving the output from the receiving side on the receiving side.

  Incidentally, in order to measure the BER, it is necessary to set a plurality of parameters to optimal values according to the measurement contents, measurement conditions, and the like. The parameters that need to be set include, for example, Data Delay that determines the time axis direction, Vth that is the reference voltage axis, and CTLE Gain for reading an attenuated signal. For these parameters, the BER is measured by changing each parameter at a plurality of points for each predetermined value, and the value of the point at which the BER is minimized is set as the optimum value.

JP 2007-274474 A

  However, in the conventional measurement, an error that occurs very infrequently cannot be accurately captured in a limited short measurement time for each point. If an error cannot be detected, an error-free state occurs in a certain section, and a problem arises in that the minimum point of the BER cannot be specified.

  In general, when an error is not detected within the measurement time and an error-free state occurs, a point at the center of an eye margin indicating a width of an error-free section is regarded as an optimum value of each parameter.

  On the other hand, when obtaining the optimum value of the parameter from the eye margin, it is necessary to obtain a stable measurement result of the eye margin. In addition, in order to set a plurality of parameters, the sequence for changing the parameters and measuring the eye margin is repeated, so that it is necessary to shorten the measurement time per measurement.

  However, if the measurement time per measurement is shortened, low-frequency errors cannot be processed well, and even if the same parameters are used, the error-free boundary between the point where the error searched for by the measurement enters and the point where the error becomes free is set. There has been a problem that the measurement result changes every time the measurement is performed, and the measurement result of the eye margin is unstable.

  In order to solve this problem, if the measurement time per measurement is lengthened, the problem arises that the total time required for parameter setting becomes longer as the number of parameters required for measurement increases.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an error rate measurement device capable of stably measuring an eye margin in a short measurement time and an eye margin measurement method of the device. The purpose is.

In order to achieve the above object, an error rate measuring apparatus according to claim 1 of the present invention transmits a test signal to a device under test W and receives an output from the device under test accompanying the transmission of the test signal. Error rate measuring device 1 that measures the bit error rate
Regarding DataDelay that determines the time axis direction, Vth that is the reference voltage axis, and the measurement time required to set each parameter of the filter,
A BER lower limit calculating unit 11a that calculates a lower limit of the bit error rate that is reliable with respect to the measurement time;
A bit error rate that is less than the lower limit of the bit error rate is regarded as error free, and a binary search is performed between two points, a point at which the bit error rate can be measured and a point at which the bit error rate becomes error free by varying the phase in a predetermined step. Phase margin measuring means 11b for measuring the difference between the left and right error-free boundaries of the phase found as a phase margin,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error-free, and a threshold voltage is varied in a predetermined step to divide the bit error rate into two points, a point at which the bit error rate can be measured and a point at which the error is free. A threshold voltage margin measuring means 11c for measuring a difference between an error-free boundary above and below the threshold voltage found by searching as a threshold voltage margin,
Eye margin calculating means 11d for calculating a value obtained by multiplying the value of the phase margin and the value of the threshold voltage margin as an eye margin value.

3. An eye margin measuring method for an error rate measuring apparatus according to claim 2, wherein a test signal is transmitted to the device under test W, and an output from the device under test accompanying the transmission of the test signal is received. Is an eye margin measuring method of the error rate measuring device 1 for measuring
Regarding DataDelay that determines the time axis direction, Vth that is the reference voltage axis, and the measurement time required to set each parameter of the filter,
Calculating a reliable lower limit of the bit error rate for the measurement time,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error free, and a binary search is performed between two points, a point at which the bit error rate can be measured and a point at which the bit error rate becomes error free by varying the phase in a predetermined step. measuring the to difference between the left and right error-free boundary of the phase found as the phase margin,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error-free, and a threshold voltage is varied in a predetermined step to divide the bit error rate into two points, a point at which the bit error rate can be measured and a point at which the error is free. measuring the difference between the upper and lower error-free border of the search to the threshold voltage found as a threshold voltage margin,
Calculating a value obtained by multiplying the value of the phase margin by the value of the threshold voltage margin as the value of the eye margin.

  ADVANTAGE OF THE INVENTION According to this invention, the influence by the error which generate | occur | produces infrequently can be made small, and the parameter search based on a stable measurement result becomes possible, measuring a phase margin and a threshold voltage margin stably in a short measurement time. .

1 is a block diagram illustrating a schematic configuration of an error rate measurement device according to the present invention. FIG. 3A is a diagram illustrating an example of a minimum value of a bit error rate, and FIG. 3B is a diagram illustrating an example of an error-free section. FIG. 4 is a diagram illustrating an example of a phase margin and a threshold voltage margin. FIG. 4 is a flowchart of an eye margin measuring method of the error rate measuring device according to the present invention. FIG. 5 is a flowchart of the phase margin measurement of FIG. 4. FIG. 5 is a flowchart of the threshold voltage margin measurement of FIG. 4.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the error rate measurement device 1 of the present embodiment transmits a test signal of a known pattern to a device under test W and receives an output from the device under test W accompanying the transmission of the test signal. The BER (bit error rate) is measured, and includes a pattern transmitting unit 2 and a pattern receiving unit 3.

  Further, the error rate measurement device 1 of the present embodiment has an auto search function for searching for and setting an optimum value of a parameter selected from a plurality of parameters necessary for measuring the BER of the device under test W.

  The parameters set by the auto search function include, for example, Data Delay for determining the time axis direction, Vth as a reference voltage axis, CTLE Gain for reading an attenuated signal, and filter parameters.

  When measuring the BER of the device under test W, the pattern transmitting section 2 generates a known pattern signal (test signal) to be input to the device under test W and transmits the signal to the device under test W.

  Although not particularly shown, the pattern transmission unit 2 includes, for example, a PRBS pattern generation unit and a programmable pattern generation unit. The PRBS pattern generation unit generates a PRBS (Pseudo-random bit sequence) pattern as a test signal of a known pattern input to the device under test W. The programmable pattern generator generates a programmable pattern including an arbitrary pattern as a test signal of a known pattern to be input to the device under test W.

  The pattern receiving unit 3 receives a signal from the device under test W accompanying the transmission of the pattern signal from the pattern transmitting unit 2 to the device under test W, and includes a parameter setting unit 11, an error rate measuring unit 12, and a display unit 13. Is provided.

  The parameter setting unit 11 sets and changes parameters, operates by acquiring a BER from the error rate measurement unit 12, and operates a BER lower limit calculation unit 11a, a phase margin measurement unit 11b, a threshold voltage margin measurement unit 11c, An eye margin calculator 11d is provided.

  The BER lower limit calculation unit 11a calculates a BER lower limit b, for example, as shown in FIG. The lower limit b of the BER is a value that is reliable with respect to the measurement time, and is calculated using a calculation formula based on statistics (1) below.

  To calculate the lower limit b of the BER, t = −ln (1-c) / (b * r) Equation (1) is used. In the equation (1), t is a measurement time required for setting each parameter (a time depending on an actual device), c is reliability (for example, 0.95), b is a lower limit of BER, and r is a transmission speed (for example, 2. 4 Gbps to 32 Gbps).

  As the lower limit value b of the BER, a measurement time t, reliability c, and transmission rate r per one time are set in advance, and b = −ln (1-c) / (t * r) obtained by modifying the above equation (1). ... It can be calculated by equation (2). In the present embodiment, a BER smaller than the BER lower limit b calculated by the BER lower limit calculator 11a is regarded as pseudo error-free.

  The phase margin measuring means 11b regards a BER calculated by the BER lower limit calculating means 11a that is less than the lower limit b of the BER as pseudo-error-free, changes the phase in predetermined steps, and varies the phase. The phase margin is measured according to the procedure described in.

  The threshold voltage margin measuring means 11c regards the BER calculated by the BER lower limit value calculating means 11a that is less than the lower limit value b of the BER as pseudo error-free, varies the threshold voltage in predetermined steps, and varies the threshold voltage. The threshold voltage margin is measured according to the procedure of the flowchart of FIG.

  The eye margin calculation unit 11d calculates the measurement result of the phase margin measurement unit 11b and the threshold voltage margin measurement unit 11c, that is, the value obtained by multiplying the measured phase margin value and the threshold voltage margin value as the eye margin value. .

  The error rate measurement unit 12 transmits a known pattern signal from the pattern transmission unit 2 to the device under test W in a state where the parameters required for the BER measurement are set by the parameter setting unit 11, and The output from the device under test W accompanying the transmission is received, and the transmitted known pattern signal and the received pattern signal are compared with each other to measure the BER.

  The display unit 13 includes, for example, a liquid crystal display, and displays a setting screen for each parameter related to BER measurement, displays a BER measurement result by the error rate measurement unit 12, and the like.

  Next, an eye margin measuring method of the error rate measuring device 1 configured as described above will be described with reference to FIGS.

  When measuring the eye margin, first, as shown in the flowchart of FIG. 4, a lower limit value b of the BER that is reliable with respect to the measurement time is calculated using the above-described equation (2) (ST1). At that time, the measurement time is set to a time depending on the actual device.

  Next, the BER calculated by the BER lower limit calculating means 11a, which is less than the lower limit b of the BER, is regarded as pseudo error-free, and the phase margin is measured according to the procedure shown in the flowchart of FIG. 5 (ST2). When measuring the phase margin, as shown in FIG. 5, first, the phase is varied by changing the phase in coarse steps, and a point at which BER measurement is possible and an error-free point are found (ST11). Next, a binary search is performed between the two points found in ST11 to find an error-free boundary on the left side (P1 in FIG. 2B and FIG. 3) (ST12). Thereafter, the phase is changed again to the point where an error occurs (ST13), and the right error-free boundary (P2 in FIG. 2 (b) or FIG. 3) is found by binary search (ST14). Then, the difference between the left error-free boundary and the right error-free boundary is set as a phase margin (ST15).

  Next, a BER calculated by the BER lower limit value calculating means 11a that is smaller than the lower limit value b of the BER is regarded as pseudo error-free, and a threshold voltage margin is measured according to the procedure shown in the flowchart of FIG. 6 (ST3). When the threshold voltage margin is measured, as shown in FIG. 6, first, the threshold voltage is varied in coarse steps to vary, and a point where BER measurement is possible and an error-free point are found (ST21). Next, a binary search is performed between the two points found in ST21 to find a lower error-free boundary (P3 in FIG. 3) (ST22). Thereafter, the threshold voltage is changed again to the point where an error occurs (ST23), and the upper error-free boundary (P4 in FIG. 3) is found by a binary search (ST24). Then, the difference between the lower error-free boundary and the upper error-free boundary is set as a threshold voltage margin (ST25).

  For the error-free boundary of the phase margin and the error-free boundary of the threshold voltage margin, the lower limit value b of the BER calculated by the equation (2) is searched, and a boundary point with the lower limit value b of the BER is found by a binary search.

  Then, an eye margin is calculated from the measured phase margin and threshold voltage margin (ST4). That is, a value obtained by multiplying the measured value of the phase margin by the value of the threshold voltage margin is calculated as the value of the eye margin.

  As described above, in the present embodiment, the lower limit of the BER that is reliable with respect to the measurement time is calculated by equation (2) based on statistics, and the BER that is less than the calculated lower limit of the BER is pseudo-error-free. , And measures a phase margin and a threshold voltage margin to calculate an eye margin necessary for searching for an optimum value of a parameter. This makes it possible to reduce the effect of infrequently occurring errors in the auto-search function by using a noise-resistant eye margin measurement, and to stably measure the phase margin and threshold voltage margin in a short measurement time, The parameter search becomes possible based on the measured result of the eye margin.

  The best mode of the error rate measuring device and the error rate measuring method according to the present invention has been described above, but the present invention is not limited by the description and the drawings according to this mode. That is, it goes without saying that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Error rate measurement apparatus 2 Pattern transmission part 3 Pattern reception part 11 Parameter setting part 11a BER lower limit calculation means 11b Phase margin measurement means 11c Threshold voltage margin measurement means 11d Eye margin calculation means W Device under test (DUT)
b Lower limit value of BER P1 to P4 Error free boundary

Claims (2)

An error rate measuring device (1) for transmitting a test signal to a device under test (W), receiving an output from the device under test accompanying the transmission of the test signal, and measuring a bit error rate,
Regarding DataDelay that determines the time axis direction, Vth that is the reference voltage axis, and the measurement time required to set each parameter of the filter,
BER lower limit value calculating means (11a) for calculating a lower limit value of the bit error rate that is reliable with respect to the measurement time;
A bit error rate that is less than the lower limit of the bit error rate is regarded as error free, and a binary search is performed between two points, a point at which the bit error rate can be measured and a point at which the bit error rate becomes error free by varying the phase in a predetermined step. Phase margin measuring means (11b) for measuring the difference between the right and left error-free boundaries of the phase found as a phase margin,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error-free, and a threshold voltage is varied in a predetermined step to divide the bit error rate into two points, a point at which the bit error rate can be measured and a point at which the error is free. A threshold voltage margin measuring means (11c) for measuring a difference between an error-free boundary above and below the threshold voltage found by the search as a threshold voltage margin;
An error rate measurement device, comprising: an eye margin calculating means (11d) for calculating a value obtained by multiplying the value of the phase margin and the value of the threshold voltage margin as an eye margin value. An eye margin measuring method of an error rate measuring device (1) for transmitting a test signal to a device under test (W), receiving an output from the device under test accompanying the transmission of the test signal, and measuring a bit error rate. So,
Regarding DataDelay that determines the time axis direction, Vth that is the reference voltage axis, and the measurement time required to set each parameter of the filter,
Calculating a reliable lower limit of the bit error rate for the measurement time,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error free, and a binary search is performed between two points, a point at which the bit error rate can be measured and a point at which the bit error rate becomes error free by varying the phase in a predetermined step. measuring the to difference between the left and right error-free boundary of the phase found as the phase margin,
A bit error rate that is less than the lower limit of the bit error rate is regarded as error-free, and a threshold voltage is varied in a predetermined step to divide the bit error rate into two points, a point at which the bit error rate can be measured and a point at which the error is free. measuring the difference between the upper and lower error-free border of the search to the threshold voltage found as a threshold voltage margin,
Calculating a value obtained by multiplying the value of the phase margin by the value of the threshold voltage margin as the value of the eye margin.

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