Digital CMOS Abbreviation F Alphabet Dictionary
Failure Rate
The failure rate of a system indicates how frequently the system experiences failures. It is typically measured in failures per year or decade for successful systems. The failure rate is not constant but varies throughout the system’s lifetime, with higher rates during the introduction and late-life stages.
Fall Time
Fall time is the time it takes for a signal to transition from a high (logical 1) to a low (logical 0) state. It describes the slope of the signal’s descending edge.
Fan-Out (BJT)
Fan-out in bipolar junction transistor (BJT) logic refers to the maximum number of stages that can be connected to the output of a BJT gate. This limit is determined by factors like base current, which draws output current and affects the high logic output.
Fan-Out (CMOS)
In CMOS logic, fan-out is the ratio of the size of the next stage to the size of the current stage in a logic chain. It can also be defined as the ratio of input capacitances between gates. Fan-out helps characterize how one gate’s output can drive subsequent gates.
Fast-Fast Corner
A fast-fast corner represents a scenario in which a finished chip exhibits both NMOS and PMOS transistors that are faster than the nominal values suggested during the design phase. This can be due to better-than-expected mobility. Chips from fast-fast corners may offer higher speed performance but can also pose challenges related to hold-time violations.
Fault
A fault represents a model of the deviation in the behavior of a circuit due to a defect. Faults can occur at various levels of abstraction, including system, logic, or transistor levels. They indicate how a defect manifests at a specific level but may not reveal the nature of the underlying defect.
Fault Coverage
Fault coverage is the percentage of possible faults that are detected when a specific set of tests is applied. It quantifies the effectiveness of the testing process, with higher fault coverage indicating a more thorough test suite.
Fermi Level
The Fermi level represents the average chemical energy of electrons in a material. It is also defined as the energy level at which the probability of finding an electron is 0.5 or equal to the probability of finding a hole. In semiconductors, the Fermi level lies within the forbidden gap, and it does not necessarily correspond to a valid energy state.
Fermi-Dirac Function
The Fermi-Dirac function is a probability distribution describing the likelihood of finding an electron at a particular energy level. It is conditional on the existence of an energy level and doesn’t indicate an absolute probability value.
Field Oxide (FOX)
Field oxide is a thick insulating oxide layer grown over non-active areas of a semiconductor wafer. It was commonly used in older LOCOS (Local Oxidation of Silicon) technologies to prevent latch-up issues. In modern technologies, shallow and deep trench technologies have largely replaced them.
FIFO (First-In-First-Out)
FIFO is a memory structure used for storing and retrieving data in sequential order, following the “first in, first out” principle. It typically consists of a shift register or RAM core with read and write pointers, along with flags indicating whether the FIFO is full or empty. FIFOs are often used in data buffering applications.
FinFET
A FinFET is a type of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) structure in which the gate wraps around a thin, raised fin-like structure on the semiconductor substrate. This design enhances control over the channel, reduces leakage current, and allows for better power efficiency.
Fixed-Point Number
A fixed-point number is a numerical representation in which the position of the binary point (or decimal point) is fixed. It means that all numbers have a consistent number of integer and fractional bits, simplifying hardware arithmetic operations.
Fixed-Point Simulation
Fixed-point simulation is a modeling technique in which all numbers and operations are represented and performed using fixed-point number formats. It helps in simulating and analyzing hardware designs with quantization effects and allows designers to determine appropriate register sizes.
FLASH (NVM)
FLASH is a category of Non-Volatile Memory (NVM) that combines high density, ease of programming, and erasure. Each cell typically consists of a double-gate transistor with thin oxides. Programming is achieved through methods like hot carrier injection or Fowler-Nordheim tunneling, and erasure is performed via Fowler-Nordheim tunneling. FLASH memories are widely used in consumer electronics for mass storage.
Flat Band Diagram
A flat band diagram represents the energy band diagram of a semiconductor device when all energy levels are flat. It doesn’t represent the equilibrium state and is characterized by a flat vacuum level. Discontinuities in the Fermi level may exist in this diagram.
Flat Band Potential
The flat band potential represents the total built-in potential at thermal equilibrium in a semiconductor device. In a MOS (Metal-Oxide-Semiconductor) capacitor, it is the reverse of the gate-to-body potential required to bring the device to a flat band state.
Flattened Design
A flattened design is a design approach where all parts of the netlist are considered to be on the same flat level, without partitions. This approach allows for more flexibility in the placement and routing of components but can increase the complexity and risk in the design process.
Flip Chip Technology
Flip chip technology is a mounting technique commonly used with Ball Grid Array (BGA) integrated circuits. Solder balls are attached to exposed metal pads on the chip, and the chip is flipped over and aligned with the corresponding footprint on the printed circuit board (PCB). Heating is then used to melt the solder balls, bonding the chip to the PCB.
Floating Point Number
A number representation where the position of the binary point (or decimal point) is flexible. It consists of a base and a mantissa, allowing for a wide range of numbers to be represented. Floating point numbers are commonly used in general-purpose processors due to their ability to represent a large range of values. However, they require large-width registers for efficient use.
Floating Point Simulation
The simulation was performed using floating point numbers and operations. High-level programming languages are often used for this type of simulation, making it easy to write, debug, and modify. Floating point simulations focus on capturing functionality and algorithmic-level information and are not intended to aid hardware design.
Floorplanning
The process of assigning specific areas of a chip to different partitions. Floorplanning helps organize the layout of a chip and involves maintaining specific area and aspect ratio requirements. Proper floorplanning can also ensure that partitions with frequent communication are placed near each other.
For (VHDL)
A looping construct in VHDL that can be used within processes. It resembles loop structures in programming languages. While “for” loops are generally synthesizable, the resulting hardware can sometimes exhibit unpredictable behavior.
For-Generate (VHDL)
A VHDL structure that allows multiple component instantiations to be declared using concise code. It is not strictly a loop and results in parallel hardware elements.
Forward-Biased PN Junction
A PN junction in which an external voltage is applied with a positive polarity to the P-side. This action narrows the depletion region, weakens the built-in electric field, and reduces the barrier to majority carriers on both sides. As a result, a large current of majority carriers flows through the junction.
Fowler–Nordheim Tunneling
A tunneling phenomenon that occurs across a triangular barrier, often associated with heavily tilted insulators under a strong electric field. It results in increased tunneling probability due to the effective reduction in barrier thickness. Fowler-Nordheim tunneling is significant in both leakage current and programming/erasure mechanisms in nonvolatile memories.
FPGA (Field-Programmable Gate Array)
An implementation platform that bridges the gap between ASICs (Application-Specific Integrated Circuits) and general-purpose processors. FPGAs offer flexibility and ease of design like processors while providing performance similar to ASICs. They consist of an array of configurable logic cells and programmable routing channels. FPGA design flow is analogous to ASIC design flow.
Full Adder
A combinational logic block that accepts three inputs and produces two outputs: a sum and a carry. It is a fundamental building block for adders and arithmetic circuits. Full adders are commonly used in N-bit adders and array multipliers.
Full Flag
A FIFO (First-In-First-Out) memory flag indicates the FIFO is full, signaling the transmitter to stop writing data to prevent overwriting unread data by the receiver. It is determined based on the positions of the read and write pointers.
Function (VHDL)
A subprogram in VHDL that can have multiple arguments but returns a single value. Functions use variable declarations and assignments. They are synthesizable if all their statements can be synthesized and are typically used for calculations and transformations that yield constant values during synthesis.
