CN109995359B - Metastable state observation system and method for edge trigger - Google Patents

Abstract

The invention provides a metastable state observation system and a metastable state observation method of an edge trigger, which comprise the following steps: edge touchA transmitter metastability observation system, comprising: the device comprises a pulse signal source, a delayer A, a delayer B, a trigger, an NRZ/RZ converter, an error code testing unit and an oscilloscope; the D end and the CP end of the trigger are respectively connected with a delayer A and a delayer B, and an oscilloscope is used for reading the input delay interval tau of the delayer A and the delayer B ₀₁ . The NRZ/RZ converter is arranged between the Q end of the trigger and the error code testing unit; and respectively counting the rising edges of the pulses at the Q end and the CP end of the trigger by using an error code testing unit. The invention has the advantages that: the observation system is simple and easy to implement, has high reliability, and has important reference value for engineering technicians and teaching personnel engaged in the metastable state characteristic research of the edge trigger.

Description

Metastable state observation system and method for edge trigger

Technical Field

The invention relates to the technical field of metastable state observation, in particular to a metastable state observation system of an edge trigger.

Background

The flip-flop is widely used in modern IT hardware circuits and systems as a high-speed memory element. In order to realize reliable storage of input data, the establishing time and the holding time regions of the input data before and after the rising edge of a clock are required to be kept constant, otherwise, a metastable state occurs, and error codes of the stored data in a trigger are caused. In the research on the internal circuit of the trigger and the clock domain crossing application of the trigger, people often need to observe the metastable state generation process. However, the metastable state process is a random process and is difficult to observe in actual work.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a metastable state observation system of an edge trigger, which can effectively solve the problems in the prior art.

In order to realize the purpose, the technical scheme adopted by the invention is as follows:

an edge-flip-flop meta-stability observation system comprising: the device comprises a pulse signal source, a delayer A, a delayer B, a trigger, an NRZ/RZ converter, an error code testing unit and an oscilloscope;

the D end and the CP end of the trigger are respectively connected with a delayer A and a delayer B, and an oscilloscope is used for reading the input delay interval tau of the delayer A and the delayer B ₀₁ 。

The NRZ/RZ converter is arranged between the Q end of the trigger and the error code testing unit;

using error code test unit to count the pulse up-going edge of Q end and CP end of trigger respectively, then according to the number of pulses

The input excitation condition is obtained by formulaBit error rate delta ₀₁ 。

The error code testing unit consists of an NI acquisition card and Labview software,

when LABVIEW programming is carried out, only data collected from an NI acquisition card port are needed to be judged by rising edges, a shift register is used for continuous counting, and a zero clearing end is compiled.

In a rising edge judgment program of data collected by the NI collection card port, data of two ports are firstly distinguished by using an index array VI, then rising edge judgment is respectively carried out by using Boolean value conversion (point-by-point) VI, and in the VI, false-true is selected in the direction. The zero clearing end adopts a method of writing data 0 into the shift register when the condition structure is false, so as to achieve the purpose of zero clearing of the data.

Further, the pulse signal source outputs 0-5V square waves, the duty ratio is 50%, and the frequency is 100Hz. Phase shifter R =100 Ω.

An observation method of an edge trigger metastable state observation system comprises the following steps:

step 1, observing through an oscilloscope to enable the distance | tau between the rising edge of the D end of the trigger and the rising edge of the CP end of the trigger ₀₁ |>|τ _01L |。

Step 2, realizing the pair of | tau ₀₁ A decreasing sweep over a build time.

Step 3, when | τ ₀₁ |<|τ _01L When I, the error code waveform can be observed at the Q end of the trigger by using an oscilloscope, and tau can be read by the oscilloscope at the moment ₀₁ Value, delta, read by the error code test unit ₀₁ The value is obtained.

Step 4, follow | τ ₀₁ Reduction of |, δ ₀₁ The value will gradually increase monotonically. When | τ ₀₁ |<|τ _01H When is delta ₀₁ The value will reach 100%. Continue to decrease | τ ₀₁ Delta if | is 0 ₀₁ The value will always remain at the 100% value.

Compared with the prior art, the invention has the advantages that: the observation system is simple and easy to implement, has high reliability, and has important reference value for engineering technicians and teaching personnel engaged in the metastable state characteristic research of the edge trigger.

Drawings

FIG. 1 is a graph of error code over time for the present invention;

FIG. 2 shows the present invention with D terminal at [ tau ] _01L ，τ _01H ]Jump schematic diagram on interval;

FIG. 3 is a waveform diagram of random bit errors at the Q terminal of the present invention;

FIG. 4 is a block diagram of a metastability observation system according to the present invention;

FIG. 5 is a circuit diagram of a metastability observation system according to the present invention;

FIG. 6 is a block diagram of an error code tester according to the present invention;

FIG. 7 is a flow chart illustrating the observation of a metastable state experiment according to an embodiment of the present invention;

FIG. 8 is a delta-tau error code plot diagram of 74HC74 establishing time in accordance with an embodiment of the present invention

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings by way of examples.

Principle of operation

Trigger setup time T at edge D _su In the region, there is an error curve as shown in fig. 1.

When the D-end data jumps from '0' at the previous moment to '1' at the next moment, the interval between the D-jump edge and the CP rising edge is tau ₀₁ And satisfy | τ _01L |>|τ ₀₁ |>|τ _01H In |, as shown in fig. 2.

A stable metastable error waveform can be observed at the Q-terminal of the flip-flop as shown in fig. 3.

In fig. 3, the random error code waveform at the Q terminal is not certain at a certain time, but has a statistical rule with τ ₀₁ From large to small, the error rate will gradually increase from 0% to 100% monotonically.

For counting CP, Q (RZ) rising edges, the mathematical relationship between the counting values is as follows:

for convenient counting, the non-return-to-zero waveform Q (NRZ) output by the Q end needs to be converted into a return-to-zero waveform Q (RZ).

Construction of metastable state observation system

The metastability observation system is constructed as a block diagram as shown in fig. 4. In order to realize the delay of the D end and the CP end, a delayer 1 and a delayer 2 are respectively connected to the D end and the CP end, and an oscilloscope is used for reading an input delay interval tau ₀₁ . Using error code test unit to count up-jumping edge of Q end pulse and up-jumping edge of CP end pulse, then obtaining error code rate delta under the condition of said input excitation according to formula (3) ₀₁ 。

If the same pulse signal source is used at the D end and the CP end, the RC delay circuit is used as the delay device, and the NRZ/RZ circuit is obtained by combining the Q end and the CP end, the time sequence shown in the figure 3 can be realized. The experimental specific circuit is shown in fig. 5.

In the circuit of fig. 5, the operating voltage was 5V, the pulse signal source model RIGOL DS1102E, the oscilloscope model Tektronix MSO58. The pulse signal source outputs 0-5V square wave with duty ratio of 50% and frequency of 100Hz. Phase shifter R =100 Ω, C ₂ A trimming capacitor of 5/20pF is used. And the AND gate adopts an integrated four 2-input end AND gate CD4081. For shaping and isolation, the NOT gate selects an integrated six-input NOT gate CD4069.

Error code testing unit

The error code testing unit is composed of an NI acquisition card and Labview software, and is shown in figure 6.

The acquisition card is NI USB-6001 and has 13 digital ports. This experiment uses two digital I/O ports, port P0.0, port P0.1.

When programming LABVIEW, only the rising edge judgment is carried out on the data collected from the ports P0.0 and P0.1, the continuous counting is carried out by using a shift register, and the zero clearing end is programmed.

In the procedure of judging the rising edge of the data collected by the data port, the data of the two ports are firstly distinguished by using an index array VI, then the rising edge is judged by respectively using Boolean value conversion (point-by-point) VI, and in the VI, the direction is selected from false-true. The zero clearing end adopts a method of writing data 0 into the shift register when the condition structure is false, so as to achieve the purpose of zero clearing of the data.

Example 1

The experimental observation of edge D flip-flops using the metastability observation system is shown in FIG. 7.

An observation method of an edge trigger metastable state observation system comprises the following steps:

step 1, let C ₁ 、C ₂ Minimum, increase C ₃ The distance between the rising edge of the D end of the trigger and the rising edge of the CP end of the trigger is | tau through observation of an oscilloscope ₀₁ |>|τ _01L |。

Step 2, fixing C ₃ Gradually increase C ₁ Realize to | τ ₀₁ A decreasing sweep over a build time.

Step 3, when | τ ₀₁ |<|τ _01L When |, the error code waveform can be observed at the Q end of the trigger by using an oscilloscope, and tau can be read by the oscilloscope at the moment ₀₁ Value, delta, read by the error code test unit ₀₁ The value is obtained.

Step 4, fixing C ₁ And C ₃ Increasing fine tuning capacitance C ₂ The value is obtained. With | τ ₀₁ Reduction of |, δ ₀₁ The value will gradually increase monotonically. When | τ ₀₁ |<|τ _01H When is delta ₀₁ The value will reach 100%. Continue to decrease | τ ₀₁ Delta if | is 0 ₀₁ The value will always remain at the 100% value.

In FIG. 5, the D flip-flop in the figure is replaced by an integrated flip-flop 74HC74 as an example of meta-stability observation. The measured data are shown in Table 1.

TABLE 1 74HC74 Integrated trigger bit error Rate data record

τ 01 (ns)	δ(％)
		-20.000	0
-10.00	0
		-5.000	0
-3.000	0
		-1.300	0
-1.289	3.32
		-1.220	13.06
-1.197	32.03
		-1.096	54.91
-1.082	62.28
		-1.059	74.84
-1.036	82.59
		-1.013	95.55
-0.850	100
		-0.500	100
0	100

τ in Table 1 ₀₁ And the waveform half height is read out from the D end and the CP end by an oscilloscope.

Monitoring the Q terminal by an oscilloscope when the value is tau ₀₁ Into [ tau ] _01L ，τ _01H ]In the interval, a metastable error occurs.

The error curves plotted from the data in Table 1 are shown in FIG. 8, τ _01L ＝1.675ns，τ _01H =1.013ns, the error code transition zone is in the range of 1.675 ns-1.013 ns.

The embodiment introduces the design idea of the metastable state observation system of the edge trigger, and provides a specific test circuit and a detailed test flow. When the delay value between the D end and the CP end of the trigger is in a certain interval in the set-up time, the error code output waveform of the Q end in the metastable state can be visually seen through the oscilloscope. In the embodiment, the integrated edge trigger 74HC74 is taken as an example, a monotone stable error code waveform of 0-100% is presented in the range of the establishment time of 1.675 ns-1.013 ns, and the test precision reaches 0.001ns.

It will be appreciated by those of ordinary skill in the art that the examples described herein are intended to assist the reader in understanding the manner in which the invention is practiced, and it is to be understood that the scope of the invention is not limited to such specifically recited statements and examples. Those skilled in the art, having the benefit of this disclosure, may effect numerous modifications thereto and changes may be made without departing from the scope of the invention in its aspects.

Claims (2)

1. An observation method of a metastable state observation system of an edge trigger is characterized in that:

the metastable state observation system of the edge trigger comprises: the device comprises a pulse signal source, a delayer A, a delayer B, a trigger, an NRZ/RZ converter, an error code testing unit and an oscilloscope;

respectively connecting a delay A and a delay B at the D end and the CP end of the trigger, and reading the input delay interval tau of the delay A and the delay B by using an oscilloscope ₀₁ ；

The NRZ/RZ converter is arranged between the Q end of the trigger and the error code testing unit;

using error code test unit to count the pulse up-going edge of Q end and CP end of trigger respectively, then according to the number of pulses

The error rate delta under the condition of the input excitation is obtained by a formula ₀₁ ；

The error code testing unit consists of an NI acquisition card and Labview software,

when LABVIEW programming is carried out, only data collected from an NI acquisition card port are needed to be judged on the rising edge, a shift register is used for continuous counting, and a zero clearing end is compiled;

in a rising edge judgment program of data collected by an NI collection card port, firstly, data of two ports are distinguished by using an index array VI, then rising edge judgment is carried out by respectively using Boolean value conversion (point-by-point) VI, and in the VI, false-true is selected in the direction; the zero clearing end adopts a method of writing data 0 into the shift register when the condition structure is false, so as to achieve the purpose of zero clearing of the data;

the observation method comprises the following steps:

step 1, observing through an oscilloscope to enable the distance | tau between the rising edge of the D end of the trigger and the rising edge of the CP end of the trigger ₀₁ |>|τ _01L |；

Step 2, realizing the pair of | tau ₀₁ L descending scanning in a building time range;

step 3, when | τ ₀₁ |<|τ _01L When I, the error code waveform can be observed at the Q end of the trigger by using an oscilloscope, and tau can be read by the oscilloscope at the moment ₀₁ Value by mistakeCode test cell readout delta ₀₁ A value;

step 4, follow | τ ₀₁ Reduction of |, δ ₀₁ The value will gradually increase monotonically; when | τ ₀₁ |<|τ _01H When is delta ₀₁ The value will reach 100%; continue to decrease | τ ₀₁ Delta if | is 0 ₀₁ The value will always remain at the 100% value.

2. The observation method of the metastable state observation system of the edge flip-flop according to claim 1, wherein: the pulse signal source outputs 0-5V square waves, the duty ratio is 50%, and the frequency is 100Hz; phase shifter R =100 Ω.

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