In digital circuits, a flip-flop is a term referring to an electronic circuit that has two stable states and thereby is capable of serving as one bit of memory. Today, the term flip-flop has come to mostly denote non-transparent (clocked or edge-triggered) devices, while the simpler transparent ones are often referred to as latches; however, as this distinction is quite new, the two words are sometimes used interchangeably (see history).
A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits. Logic gates are primarily implemented electronically using diodes or transistors, but can also be constructed using electromagnetic relays, fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements.
In Boolean logic, the majority function (also called the median operator) is a function from n inputs to one output. The value of the operation is false when n/2 or more arguments are false, and true otherwise. Alternatively, representing true values as 1 and false values as 0, we may use the formula The "−1/2" in the formula serves to break ties in favor of zeros when n is even; a similar formula can be used for a function that breaks ties in favor of ones.
In Boolean functions and propositional calculus, the Sheffer stroke, named after Henry M. Sheffer, written "|" or "↑", denotes a logical operation that is equivalent to the negation of the conjunction operation, expressed in ordinary language as "not both". It is also called the alternative denial, since it says in effect that at least one of its operands is false. In Boolean algebra and digital electronics it is known as the NAND operation ("not and").
In digital logic, an inverter or NOT gate is a logic gate which implements logical negation. The truth table is shown on the right. This represents perfect switching behavior, which is the defining assumption in Digital electronics. In practice, actual devices have electrical characteristics that must be carefully considered when designing inverters. In fact, the non-ideal transition region behavior of a CMOS inverter makes it useful in analog electronics as a class A amplifier (e.g.
Fan-out is a measure of the ability of a logic gate output, implemented electronically, to drive a number of inputs of other logic gates of the same type. In most designs, logic gates are connected together to form more complex circuits, and it is common for one logic gate output to be connected to several logic gate inputs. The technology used to implement logic gates usually allows gate inputs to be wired directly together with no additional interfacing circuitry required.
In computer science, the Toffoli gate (also CCNOT gate), invented by Tommaso Toffoli, is a universal reversible logic gate, which means that any reversible circuit can be constructed from Toffoli gates. It is also known as the "controlled-controlled-not" gate, which describes its action.
A transmission gate is an electronic element. It is a good non-mechanical relay, built with CMOS technology. Sometimes known as an analog gate, analogue switch or electronic relay depending on its use. It is made by the parallel combination of an nMOS and a pMOS transistor with the input at the gate of one transistor being complementary to the input at the gate of the other.
The Fredkin gate is a computational circuit suitable for reversible computing, invented by Ed Fredkin. It is universal, which means that any logical or arithmetic operation can be constructed entirely of Fredkin gates. The basic Fredkin gate is a controlled swap gate that maps three inputs (C, I1, I2) onto three outputs (C, O1, O2). The C input is mapped directly to the C output. If C = 0, no swap is performed; I1 maps to O1, and I2 maps to O2.
The AND gate is a digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output (1) results only if both the inputs to the AND gate are HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output results. In another sense, the function of AND effectively finds the minimum between two binary digits, just as the OR function finds the maximum.
The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is HIGH, a LOW output (0) results. In another sense, the function of OR effectively finds the maximum between two binary digits, just as the complementary AND function finds the minimum.
In semiconductor design, standard cell methodology is a method of designing application-specific integrated circuits (ASICs) with mostly digital-logic features. Standard cell methodology is an example of design abstraction, whereby a low-level VLSI-layout is encapsulated into an abstract logic representation (such as a NAND gate).
The Muller C-element, or Muller C-gate, is a commonly used asynchronous logic component originally designed by David E. Muller. It applies logical operations on the inputs and has hysteresis. The output of the C-element reflects the inputs when the states of all inputs match. The output then remains in this state until the inputs all transition to the other state.
The Controlled NOT gate (also C-NOT or CNOT) is a quantum gate that is an essential component in the construction of a quantum computer. It can be used to disentangle EPR states. Specifically, any quantum circuit can be simulated to an arbitrary degree of accuracy using a combination of CNOT gates and single qubit rotations.
The XOR gate (sometimes EOR gate) is a digital logic gate that implements exclusive disjunction - it behaves according to the truth table above. A HIGH output (1) results if one, and only one, of the inputs to the gate is HIGH (1). If both inputs are LOW (0) or both are HIGH (1), a LOW output (0) results. XOR gate is short for exclusive OR. This means that precisely one input must be 1 (true) for the output to be 1 (true). A way to remember XOR is "one or the other but not both.
NAND gates are one of the two basic logic gates from which any other logic gates can be built. Due to this property, NAND and NOR gates are sometimes called "universal gates". However, contrary to popular belief, modern integrated circuits are not constructed exclusively from a single type of gate. Instead, EDA tools are used to convert the description of a logical circuit to a netlist of complex gates or transistors.
The XNOR gate (sometimes spelled "exnor" or "enor") is a digital logic gate whose function is the inverse of the exclusive OR gate. The two-input version implements logical equality, behaving according to the truth table to the right. A HIGH output (1) results if both of the inputs to the gate are the same. If one but not both inputs are HIGH (1), a LOW output (0) results.
The NOR gate is a digital logic gate that implements logical NOR - it behaves according to the truth table to the right. A HIGH output (1) results if both the inputs to the gate are LOW (0). If one or both input is HIGH (1), a LOW output (0) results. NOR is the result of the negation of the OR operator. NOR is a functionally complete operation—combinations of NOR gates can be combined to generate any other logical function.
Fan-in is the number of inputs of an electronic logic gate. For instance the 'fan-in' for the AND gate shown below is 3. Logic gates with a large fan-in tend to be slower than those with a small fan-in, because the complexity of the input circuitry increases the input capacitance of the device. A related concept is fan-out, which is the number of logic inputs that a given logic output drives.
A molecular logic gate is a molecule that performs a logical operation on one or more logic inputs and produces a single logic output. Much academic research is dedicated to the development of these systems and several prototypes now exist. Because of their potentional utility in simple arithmetic these molecular machines are also called moleculators. Molecular logic gates work with input signals based on chemical processes and with output signals based on spectroscopy.
Like NAND gates, NOR gates are so-called "universal gates" that can be combined to form any other kind of logic gate. For example, the first embedded system, Apollo Guidance Computer, was built exclusively from NOR gates, about 5,600 in total for the later versions. Today, contrary to popular belief, integrated circuits are not constructed exclusively from a single type of gate.
A Pulse transition detector is used in flip flops in order to achieve edge triggering in the circuit. It merely converts the clock's rising edge to a very narrow pulse. The PTD consists of a delay gate (which delays the clock signal) and the clock signal itself passed through a NAND gate and then inverted. The benefit of edge triggering is that it removes the problems of zeroes and ones catching associated with pulse triggered flipflops (eg. master slave flip flops).
A diode-OR circuit is used in electronics to isolate two or more voltage sources. There are two typical implementations: When a DC supply voltage needs to be generated from one of a number of different sources, for example when terminating a parallel SCSI bus, a very simple circuit like this can be used: In digital electronics a diode-OR circuit is used to derive a simple Boolean logic function.
Reconvergent fan-out is a technique to make VLSI logic simulation less pessimistic. Static timing analysis tries to figure out the best and worst case time estimate for each signal as they pass through an electronic device. Whenever a signal passes through a node, a bit of uncertainty must be added to the time required for the signal to transit that device.