JP2571082B2 - Transmission line length measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a transmission line length measuring device for measuring a transmission line length from a reflected waveform obtained by transmitting a pulse to a transmission line having an open end, and more particularly to a plurality of transmission line length measuring devices. In an integrated circuit test device having test pins of the type described above, it is used for highly accurate measurement of the transmission line length from the test pattern output / test result judgment circuit installed corresponding to the test pins to the input / output pins of the circuit under test. The present invention relates to a suitable transmission line length measuring device.

(Prior Art) In the timing correction necessary to maintain the test timing accuracy of the integrated circuit test apparatus, the test target is output from a test pattern output / test result determination circuit installed corresponding to the test pin of the integrated circuit test apparatus. One of the main processing items is to correct a timing error caused by variation between test pins in a transmission line length to an input / output pin of a circuit. Conventionally, in such a measurement of the transmission line length, a reference timing generating circuit RTG capable of delay control of the output timing with high accuracy and high time resolution is prepared as in an example of the prior art shown in FIG. The intermediate level of the first rising edge a of the reflected waveform obtained by transmitting the test pulse from the test pulse generating circuit DR with the input / output pin 2 of the circuit 1 not connected and the end point of the transmission line 3 opened. Is set as the threshold level input RV of the test result determination circuit SD, and the reference timing is moved in accordance with the bisection method or the like near the rising prediction timing of the rising edge a. 1 is detected by the test result determination circuit SD, and the phase difference from the reference timing generation circuit RTG when the phase difference becomes zero is determined from the delay set value of the reference timing generation circuit RTG. The timing Ta of the rising edge a is determined, and then the intermediate level of the second rising edge b of the reflection waveform is set as the threshold level input RV of the test result determination circuit SD, and the same operation as described above is performed. The timing Tb of the second rising edge b is obtained, and (Tb−Ta)
/ 2 was calculated to measure the propagation delay time of the transmission line length.

(Problems to be Solved by the Invention) As described above, in the prior art, a high-accuracy measurement requires a reference timing generating circuit capable of performing delay control with high accuracy and high time resolution, and the measuring instrument becomes expensive. Since the timing measurement is performed by the bisection method or the like, a plurality of reference timing setting / skew detection operations are required for one measurement, so that there is a problem that the measurement takes time.

(Means for Solving the Problems) The present invention solves the conventional problems and realizes a transmission line length measuring apparatus which can measure in a short time, with high accuracy and high time resolution, and has a simple circuit configuration. In a transmission line length measuring device that measures a transmission line length if a reflected waveform is obtained by sending a pulse to a transmission line that is open at the far end, a reflected wave having a constant repetition period, and the reflected wave are repeated. A timing comparison pulse signal having a slightly different period is used as a common input signal to be measured, the threshold value of the input signal to be measured can be controlled, and the logic level changes in accordance with the ideological polarity between the input signals to be measured. Output a phase difference information signal,
Two independent phase difference detection circuits, a gate circuit that passes the branch signal of the timing comparison pulse signal only while the phase difference information signals of the two phase difference detection circuits do not match, and an output of the gate circuit A transmission line length measuring device, comprising: a count for counting the number of signal pulses.

(Operation) The transmission line length measuring apparatus of the present invention repeats the timing of the first rising edge and the timing of the second rising edge of the step-like rising edge generated by reflection individually, slightly different from the reflected wave. Directly compares the rising edge timing of the timing comparison pulse with a rate with the phase difference detection circuit, and measures the transmission line length (propagation delay time) with high precision by simple digital processing of the comparison result (phase difference information) of the two. can do. The measurement accuracy is mostly determined by the time resolution of the phase difference detection circuit and the stability of the repetition rate of the timing comparison, and the measurement time resolution is determined by the repetition rate difference between the reflected wave and the timing comparison pulse signal. Can be realized,
There is no need for a high-accuracy, high-time-resolution reference timing signal generator or complicated oscillation control circuit.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. The embodiment is merely an example, and it goes without saying that various changes or improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows an embodiment of the basic circuit configuration of the present invention. In the stepped rising edge of the reflected wave RF obtained by opening the far end of the transmission line 3 having the line length of the propagation delay time T, the first rising edge is a, and the second rising edge is b. The first and second rising edges a and b have a timing shift of 2T. Phase difference detection circuits S1 and S2 capable of controlling the threshold value of the input signal are provided. The phase difference detection circuit S1 compares the phase difference between the first rising edge a and the rising edge of the timing comparison pulse PR. For this purpose, both signals are applied as input signals to be measured to signal input terminals to be measured T ₁ and T ₁ ′, and reference level inputs R 11 and R 11 for determining an input signal threshold value.
The intermediate level of the first rising edge a and the intermediate level of the timing comparison pulse PR are set in R12. Similarly, in order to compare the phase difference between the second rising edge b and the rising edge of the timing comparison pulse PR, the phase difference detection circuit S2 determines that the two signals are input signals to be measured as signal input terminals T ₂ ,
The intermediate level of the second rising edge b and the intermediate level of the timing comparison pulse PR are set to reference level inputs R21 and R22 which are added to T ₂ 'and determine the threshold value of the input signal.
The phase difference detection circuits S1 and S2 output a high level as positive phase shift information when the timing of the timing comparison pulse PR is delayed compared with the other timing, and as the negative phase shift information when the timing is opposite, NR that outputs low level
Z (Non-Return to Zero) phase difference information signal OUT + 1, OUT
+2 is output. Phase difference information signal OUT + 1 and OUT
+2 is exclusive-ORed by the EX-OR gate 4, and the timing comparison pulse PR and the output signal of the EX-OR gate 4
EOR is ANDed by the AND gate 5, and the timing comparison pulse P is output only when the output EOR of the EX-OR gate 4 is high.
R is output from the AND gate 5. The output signal AND of the AND gate 5 is input to the clock terminal CK of the counter 6, and the number of pulses is counted.

FIG. 2 is a time chart for explaining the operation principle of the present invention. The repetition rate of the reflected wave RF is f ₁ and the period is T _1, and the repetition rate f ₁ −Δf slightly different from the reflected wave RF
And the timing comparison pulse PR is set to the period T ₁ + ΔT.
The phase difference between the first rising edge a of the reflected wave RF and the rising edge of the timing comparison pulse PR is determined by the phase difference detection circuit S1 for each first rising edge a of the reflected wave RF. A phase difference between the edge b and the rising edge of the timing comparison pulse PR is detected by the phase difference detection circuit S2 for each second rising edge b of the reflected wave PF, and the first and second rising edges a and b are detected.
Only when the timing is earlier than the rising edge of the timing comparison pulse PR, the NRZ high level indicating a positive phase difference is continuously output as the phase difference information signals OUT + 1 and OUT + 2. For example, if the duty ratio of the timing comparison pulse PR is 50%, the phase difference information signal OUT
+1, and OUT + 2 NRZ high-level signal of a, T ₁ ·
Times satisfying (T ₁ + ΔT) / 2ΔT are continuously output, and the number of repetitions No of the timing comparison pulse PR output within this time is No = T ₁ / 2ΔT. Therefore, if No is determined, the time resolution ΔT is determined as in the following equation.

ΔT = T ₁ / 2No In the basic circuit configuration of FIG. 1, reference levels R11 and R21 for determining input threshold values of the first and second rising edges a and b.
By setting either of them to be higher than the high level of the reflected wave RF, the phase difference information output can always be fixed to the low level. Therefore, while the other phase difference information output is at the high level, the timing comparison pulse PR is output by the counter. It can be counted and the number of repetitions No is obtained. Next, the reference level R11 and R21 are first again
And the second rising edges a and b are set equal to the intermediate level, the output timings of the phase difference information signals OUT + 1 and OUT + 2 are shifted in accordance with the timing shift of the first and second rising edges a and b. it can. Phase difference information signal OUT +
When only one of OUT1 and OUT + 2 is at the high level, the counter 6 counts the timing comparison pulse PR, and the counter N and the repetition counting circuit N of the timing comparison pulse PR within one cycle of the phase difference information signals OUT + 1 and OUT + 2. The timing difference 2T between the first and second rising edges a and b from ΔT shown in FIG.
Can be calculated as 2T = N ・ ΔT / 2, so that the propagation delay time T of the transmission line to be measured can be obtained by T = N ・ ΔT / 4.

Since the repetition rate is equal to the reciprocal of the period, the difference Δf between the repetition rate of the reflected wave RF and the timing comparison pulse PR can be expressed as follows.

Δf = ΔT · f ₁ ² /(ΔT.f ₁ +1) From the above equation, for example, the repetition rate of the pulse to be measured is 50
When MHz, 1ps ± 0.001p as measurement time resolution ΔT
If s is required, Δf may be set to about 2499.875 ± 2.5 Hz. When a synthesizer is used as a signal source, the repetition rate can easily achieve a resolution of about 1 Hz and a short-term stability of about 1 × 10 ⁻¹¹ / minute, so that a high time resolution can be easily realized.

Factors governing the measurement accuracy include the stability of the repetition rate of the timing comparison pulse PR and the phase difference detection circuits S1, S
A detection resolution of 2 is possible. The stability of the repetition rate can be sufficiently obtained by using a synthesizer as described above.

By applying a circuit (patent pending) as shown in FIG. 3 (a) as the phase difference detection circuit, high resolution can be realized. FIG. 3B is a time chart for explaining the operation principle of the circuit shown in FIG. 3A.
This is to standardize the logic level of the measured pulse P1 and the timing comparison pulse PR separately with the level normalization circuits LV1 and LV2,
The difference between the standardized signals is directly amplified by the differential amplifier circuit D1, and the amplified signal D
Pulse generator SBG based on the rising edge of
The data is taken into the latch circuit L1 by the strobe pulse SB generated in step (1). The amplified signal D ± is the measured pulse P
1.The logic level shifts to low or high only during the timing shift of the timing comparison pulse PR, and the logic level changes to an intermediate level otherwise, so if the polarity of the data input given to the latch circuit L1 is appropriately selected, Only when the rising timing of the measured pulse P1 is earlier than that of the timing comparison pulse PR, that is, when there is a positive phase shift, the output Q of the latch circuit L1 can be made to output a high level. The detection resolution is determined by the amplification factor during the transient response of the differential amplifier circuit and the switching speed of the transistors that make up the entire circuit.
Time resolution of several ps can be easily realized by using Si bipolar process technology. Therefore, a transmission line length measuring device having both the measurement time resolution and the time accuracy on the order of ps can be realized by the present invention.

(Effects of the Invention) As is apparent from the above description, according to the present invention, in a transmission line length measuring apparatus for measuring a transmission line length from a reflected waveform obtained by transmitting a pulse to a transmission line open at the far end,
A reflected wave having a constant repetition period, and a timing comparison pulse signal whose repetition period is slightly different from the reflected wave are used as a common input signal to be measured, and the threshold value of the input signal to be measured can be controlled, and Two independent phase difference detection circuits that output a phase difference information signal whose logic level changes in accordance with the phase polarity between the input signals to be measured, and the phase difference information signals of the two phase difference detection circuits match. Only during the absence
By providing a gate circuit for passing the branch signal of the timing comparison pulse signal and a count for counting the number of output signal pulses of the gate circuit, a reference timing signal generator having high accuracy and high time resolution as in the related art can be provided. The measurement of the transmission line length (propagation delay time) with high accuracy and high time resolution can be realized in a short time without requiring a complicated oscillation control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional block diagram showing one embodiment of a basic circuit configuration of a transmission line length measuring device according to the present invention, and FIG. 2 shows an operation principle of the transmission line length measuring device according to the present invention. FIGS. 3 (a) and 3 (b) are a circuit block diagram showing an embodiment of a circuit configuration applicable to a phase difference detection circuit which is one component of the present invention, and FIGS. FIG. 1 is a functional block diagram showing one embodiment of the prior art. 1 ... circuit under test, 2 ... input / output pins, 3 ... transmission line, 4 ... EX-OR gate, 5 ... AND gate, 6 ... counter, T ... propagation delay time, DR ... test Pulse generating circuit, RF: reflected wave, a: first rising edge, b:
2nd rising edge, PR: timing comparison pulse, S
1, S2: phase difference detection circuit, R11, R12, R21, R22: input signal reference level, OUT + 1, OUT + 2: phase difference information signal, EO
R: Output of EX-OR gate, AND: Output of AND gate, C
K: Clock input terminal, LV1, LV2: Level normalizing circuit, D1: Differential amplifier circuit, D ±: Differential amplified signal, SBG
…… Strobe pulse generation circuit, SB …… Strobe pulse, L1… Latch circuit, Q… Latch circuit output signal, RT
G: Reference timing signal generation circuit, SD: Test result judgment circuit, RV: Threshold level input.

Claims (1)

(57) [Claims] A transmission line length measuring device for measuring a transmission line length from a reflection waveform obtained by transmitting a pulse to a transmission line having an open end, wherein a reflected wave having a constant repetition period;
And a timing comparison pulse signal whose repetition cycle is slightly different from the reflected wave is used as a common input signal to be measured, the threshold value of the input signal to be measured can be controlled, and the phase polarity between the input signals to be measured is Two independent phase difference detection circuits for outputting a phase difference information signal whose logic level changes according to the timing comparison pulse signal only when the phase difference information signals of the two phase difference detection circuits do not match. A transmission line length measuring device, comprising: a gate circuit for passing the branch signal of the above; and a count for counting the number of output signal pulses of the gate circuit.