JP2532229B2 - Transmission line parameter measuring device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a transmission in which a measurement input signal and a reflection signal are sampled, digitized, and then subjected to signal processing so that transmission path parameters can be obtained with high accuracy. The present invention relates to a road parameter measuring device.

[Prior art and its problems]

In testing an integrated circuit having a large number of terminals, it is very important to input a large number of signals to those terminals with a known phase difference (time difference). Therefore, conventionally, a delay circuit is provided between the terminal of the signal source and the terminal of the integrated circuit under test, and by adjusting them, the phase of the signal at each terminal is adjusted.

The phase difference (delay difference) between the signals is more important than the absolute value of the phase of the signal at each terminal. First, a time domain reflectometer is constructed and the delay between the signal source and each terminal is measured and adjusted so as to minimize the delay difference between them. Therefore, conventionally, the delay has been calculated by a propagation delay time measuring device as shown in FIG.

In FIG. 2A, a post-step signal is introduced to the stop input terminal 8 of the time interval counter 10 via the switch 1, the resistor 5, and the terminal 1, the high speed buffer 3, and the terminating resistor 4. The step signal is further transmitted to the transmission line 67 and the socket terminal 7 of the device under test (integrated circuit) via the switch 6. A pulse is applied to the start input terminal of the counter 10 from the terminal 2 at a fixed time before the step is applied to the terminal 1, and the counter starts counting at the time t ₀ .

FIGS. 2B and 2C show changes with time in the voltage at the stop input terminal 8 when the switch 6 is off and on, respectively.

In FIG. 2B, the step signal rises near time t ₁₁ and the reflection signal from the switch 6 rises near time t ₁₂ . Therefore, the time interval t ₁₂ -t ₁₁ is twice the propagation delay time between the switch 6 and the sampling point (connection point of the resistor 5 and the transmission line to the switch 6) sp.

Figure 2 (c), the time interval t ₂₂ -t ₂₁ are extended from the case of (b) of FIG. 2 by twice the propagation delay time of the transmission line 67.

Since t ₁₁ −t ₀ = t ₂₁ −t ₀ is selected as described above, the propagation delay time t ₆₇ of the transmission line ₆₇ is obtained by the following equation.

2t ₆₇ = (t ₂₂ −t ₂₁ ) − (t ₁₂ −t ₁₁ ) = (t ₂₂ −t ₂₁ + (t
₂₁ −t ₀ )) − (t ₁₂ −t ₁₁ + (t ₁₁ −t ₀ )) = (t ₂₂ −t ₀ )
- (t ₁₂ -t ₀₎ Thus, t ₂₂ -t ₀ by start the count in counter 10 at time t ₀ (optional), and ends respectively at the start time t ₂₂ and t ₁₂ of the reflected signal and t ₁₂ - t ₀ is obtained, and thus t ₆₇ is obtained.

 This method has various drawbacks.

Since the above-mentioned device uses high-speed steps, waveform rounding or ringing occurs due to the mismatch of the transmission line, and the trigger level of the counter 10 (v ₁₂ and v ₂₂ in (b) and (c) of FIG. 2) is reduced. It is difficult to set. That is, the indicated value of the counter 10 changes due to unnecessary components of the waveform (ringing, rounding, etc.) even at the same step input and the same trigger level.
When the step size is changed, the trigger range is detailed to determine where to set the trigger level (for example, the middle point of the trigger range).
Select This process can be very cumbersome and take minutes.

Further, it is impossible to correct the waveform distortion due to the difference in the stray capacity of the socket terminals.

[Object of the Invention]

It is an object of the present invention to eliminate the above-mentioned drawbacks by sampling the step response waveform of the transmission line, digitizing it, storing it, and performing signal processing on it.

[Outline of Invention]

In one embodiment of the present invention, the step signal input to the transmission line and its reflection signal are sampled, digitized, and then processed. The sampled waveform (digital data) is a signal waveform displayed by expanding the time axis.

The influence of ringing is eliminated by processing the digital data, and the start time of the step waveform is determined from the relative position of the step height. The start time of the reflected wave is also determined from the relative relationship between the reflected signal and the input step signal.

Furthermore, from the rising waveform of the signal, the terminal capacitance is estimated and its influence on the propagation delay time measurement is corrected.

Example of Invention

FIG. 1 shows a block diagram of a transmission line parameter measuring apparatus according to one embodiment of the present invention and a signal waveform diagram observed. In FIG. 1A, parts having the same functional performance as in FIG. 2A are given the same reference numerals. The part of FIG. 1 (a) different from that of FIG. 2 (a) will be described below.

The sampler 11 samples the signal input from the resistor 5 and inputs it to the digitizer 12. The digitized signal waveform data is continuously stored in the memory 13 for a certain period. The calculation / control unit 14 calculates transmission line parameters from the signal waveform data in the memory 13 as described later. Calculation / control unit
14 also controls the sampler 11, digitizer 12, memory 13 and other peripheral devices to perform well known data collection and calculations. The pulse input from the terminal 2 synchronizes the sampling operation of the sampler 11 and other devices.

In one embodiment of the present invention, the step signal input to the terminal 1 is a rectangular wave having a repetition frequency of 10 MHz, and the waveform data stored in the memory 13 with a time resolution of 10 ps is 10,000 points. Is not limited.

Although the transmission line 46 is inserted between the sampling point sp and the switch 6 in FIG. 1A, it is common to the socket terminals 71 to 75 to be measured and the transmission line up to the sampling point sp. Therefore, it is ignored for the purpose of adjusting the difference in delay time. The switch 6 is instructed by the calculation / control unit 14 to transmit a transmission line 67 connecting the socket terminals 71, ..., 75 to the switch 6.
Propagation delay time is obtained by switching 1 to 675 sequentially.

FIG. 1B shows a sampler input waveform (and stored waveform data) when measuring one of the transmission lines 671, to 675.

The calculation method for obtaining the transmission line parameters from the waveform data stored in the memory will be described below.

(A) Propagation delay time measurement 1. From the waveform data of 10 points before the rise of the step signal,
V ₀ is obtained as the average voltage and is used as the base value of the signal waveform.

2. The voltages V _u and V _b at the first maximum and minimum points in the ringing at the rising edge of the step signal are obtained using numerical differentiation. The average V ₃ (= (V _u + V _b ) / 2) of V _u and V _b is calculated.

3. The voltage V ₁ (eg V ₁ = which divides by a constant ratio between the voltages V ₀ and V ₃
χ V ₃ + (1-χ) V ₀ ; 0 <χ <= 1) is selected, and the time t _{1 at} which V ₁ is turned off for the first time after step application to the rising edge of the signal is obtained.

4. Maximum value V _{t of} the signal waveform existing within one period of the rectangular wave
Ask for.

5. Find the voltage V ₂ that divides V _t and V ₃ in a constant ratio, and find the time t _{2 at} which the waveform first cuts V ₂ with the reflected signal. (For example, V ₂ = yV <sub>t
+ (1-y) V 3</sub> ; 0 <y <= 1) 6.t propagation delay time of reciprocating between ₂ -t ₁ socket terminal and the selected sampling point sp from is determined.

(B) Effect of load capacity of socket terminal In FIG. 1 (c), the rising edge of the reflected signal is exaggerated more slowly. The part indicated by R in the figure is about 20
It includes 0 data points, and the waveform is approximated by the following formula. Signal waveform is a time t of the function V (t), V (t ) = V t (1-2exp (- (t-t s) / RC))).

Here, V _t is the input step voltage amplitude, V (t) is the reflected signal waveform, C is the far end load capacitance of the transmission line, R is the characteristic impedance (resistance 50Ω) of the transmission line, and t _s is a constant.

From the above equation, ln [(1-V (t) / V t) / 2 ] _{= t s / (RC) -t} / (R
C).

Here, each data point is time h _i (i = 1, 2, ... N),
If −ln [(1-V (h _i ) / V _t ) / 2] for each h _i is y _i, and t _s / (RC) is k, and w = 1 / RC, then y _i = -K + wh _i . However, the origin of h _i may be selected appropriately.

When w is estimated by the method of least squares, Becomes From this w, C can be obtained as C = 1 / (wR).

(C) Precision of propagation delay time measurement In the propagation delay time measurement, when it is known how much the capacitance C affects the rounding of the waveform at the socket terminal, the measurement accuracy can be improved by correction.

Propagation delay time of the signal waveform, propagation delay time t _a, although they respect t _b is represented as the propagation delay time t _c when continues, a ^{_{t c 2 t a 2 + t}} b 2.

Therefore, if the influence (CR) due to C is several times the standing time of the original waveform, t ₂ that determines the propagation delay time is t ₂ −
(CR) can improve accuracy.

The same idea can be applied when the impedance loaded on the socket terminal is not the capacitance. The inductance value and the resistance value of the inductance in the inductance load and the mismatched resistance termination are also obtained, and similarly used for the correction of the propagation delay time.

〔The invention's effect〕

As described above with respect to one embodiment of the present invention, by carrying out the present invention, it is possible to easily and automatically measure the propagation delay time of the transmission line and the loaded terminal impedance. Further, the propagation time can be refined by the measured load terminal capacitance, which is useful for practical use.

[Brief description of drawings]

FIG. 1 is a block diagram of a transmission parameter measuring device according to an embodiment of the present invention and a signal waveform diagram observed. FIG. 2 is a block diagram of a conventional propagation delay time measuring device and a waveform diagram observed. 1: Step signal input terminal; 2: Pulse input terminal; 3: Input high-speed buffer; 4,5: Resistance; 6: Switch; 46,47,671, ~, 675: Transmission line; 7,71, ~, 75: Socket terminal ; 8: Stop input terminal; 9: Stop input terminal; 10: Time interval counter; 11: Sampler; 12:
Digitizer; 13: memory; 14: calculation / control unit; sp: sampling point.

Claims (4)

(57) [Claims] 1. Input means (1, 3, 4, 6) for inputting a measurement input step signal to one terminal of a transmission line under measurement (671-675), and the measurement generated at the one terminal. Data collecting means (2, 5, 11, 13) for sampling and digitizing the input step signal for measurement and the reflection signal of the measurement input step signal from the transmission path under measurement, and then storing it as waveform data in a memory; Receiving the waveform data from the data collecting means, determining the rising time of the measurement input step signal and the rising time of the reflected signal, and the propagation delay of the measured transmission line from these determined rising times. In a transmission line measuring device having a calculating means (14) for calculating time, the reflection signal resulting from a load impedance connected to the other terminal (71-75) of the transmission line under measurement. Transmission path parameter measurement device and corrects a measurement error of the rise time of the. 2. A rising time of the measuring input step signal is a time at which the measuring input step signal first takes an average value of the first two extreme values of the measuring input step signal. The transmission path parameter measuring device according to claim 1. 3. The rising time of the reflection signal is a time at which the reflection signal first takes an average value of the average value and the maximum value of the reflection signal. The transmission line parameter measuring device according to the second aspect. 4. When the load impedance is a capacitance having a capacitance value C and the characteristic impedance of the measured transmission line is R,
The transmission path parameter measuring device according to claim 3, wherein C × R is subtracted from the rising time of the reflected signal to perform correction.