engineering

Random flip-flop

Random flip-flop is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Random flip-flop rather than just read about it. In short: Random flip-flop (RFF) is a theoretical concept of a non-sequential logic circuit capable of generating true randomness. By definition, it operates as an "ordinary" edge-triggered clocked flip-flop, except that its clock input acts randomly and with probability p = 1/2.

Key takeaways

Random flip-flop belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Random flip-flop to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Random flip-flop from memory before moving on to harder problems.

Reference excerpt

Random flip-flop (RFF) is a theoretical concept of a non-sequential logic circuit capable of generating true randomness. By definition, it operates as an "ordinary" edge-triggered clocked flip-flop, except that its clock input acts randomly and with probability p = 1/2. Unlike Boolean circuits, which behave deterministically, a random flip-flop behaves non-deterministically. By definition, a random flip-flop is electrically compatible with Boolean logic circuits, and when they are used together, RFFs make up a full set of logic circuits capable of performing arbitrary algorithms, realizing a Probabilistic Turing machine.

Symbol

Random flip-flops come in all varieties in which ordinary, edge triggered clocked flip-flops do, for example: D-type random flip-flop (DRFF). T-type random flip-flop (TRFF), JK-type random flip-flop (JKRFF), etc. Symbols for DRFF, TRFF and JKRFF are shown in Fig. 1.

While varieties are possible, not all of them are needed: a single RFF type can be used to emulate all other types. Emulation of one type of RFF by a different type of RFF can be done using the same additional gates as for ordinary flip-flops. Examples are shown in Fig. 2.

Practical realization of random flip-flop By definition, the action of a theoretical RFF is truly random. This is difficult to achieve in practice and is probably best realized through use of physical randomness. An RFF, based on the quantum-random effect of photon emission in a semiconductor and its subsequent detection, has been demonstrated to work well up to a clock frequency of 25 MHz. At a higher clock frequency, the subsequent actions of the RFF become correlated. This RFF has been built using bulk components and the effort resulted only in a handful of units. Recently, a monolithic chip containing 2800 integrated RFFs based on quantum randomness has been demonstrated in a Bipolar-CMOS-DMOS (BCD) process.

Applications

One straightforward application of an RFF is generation of random bits, as shown in Fig. 3. Since each RFF operates independently of the others, a group of N RFFs can generate N bits per clock, thus the overall generation throughput of a random number generator is only limited by the number of available RFFs and their maximum operating clock frequency. The biggest difference between an RFF and a true random number generator is that a plethora of RFFs can work concurrently, independently of each other, with or without any synchronicity among them. This is useful in stochastic computing, also known as Random Pulse Computing (RPC)[1], where many information-processing circuits work in parallel. RFF could also find its use in prosthetic implants such as artificial cochlear or prosthetic limbs using, near-sensor image processing as well as in artificial intelligence processors. Furthermore, in consideration of its high speed, a single RFF can be used to generate on the order of hundred thousand 256-bit cryptographic keys per second, or nonce data, without requiring any special or proprietary protocol to communicate with, making it a potentially indispensable piece of security hardware such as IoT devices, smart cards, car keys, as well as of any computer or digital communication device. While the technology of realizing an RFF on a chip is young, it is conceivable that in the future, the RFF, as an electronic element, will appear in universal logic chips (such as 7400-series integrated circuits), in Application Specific Integrated Circuits (ASIC), and in Field-Programmable Gate Array (FPGA) chips, thus facilitating designs that could benefit from it.

References

Illustrations

Worked examples

Example 1 — a first encounter with Random flip-flop

Start with the simplest possible case. Write down what Random flip-flop claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Random flip-flop before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Random flip-flop ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Random flip-flop

In research: Random flip-flop appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Random flip-flop in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Random flip-flop is common in secondary-school and first-year university syllabi. It links to neighbouring topics Digital electronics, Electronic engineering, Logic gates, so understanding it makes those chapters shorter.
In everyday life: Look for Random flip-flop outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Random flip-flop in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Random flip-flop means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Random flip-flop out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Random flip-flop in simple terms?

Why does Random flip-flop matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Random flip-flop?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Random flip-flop.