Digital CMOS Abbreviation A Alphabet Dictionary
Acceptor
An acceptor is a type of dopant added to a semiconductor material, typically from group 13 of the periodic table. When ionized, acceptors create an additional empty state in the valence band of the semiconductor, resulting in a “hole” in the electron structure. This increases the material’s conductivity and leads to a higher concentration of holes compared to electrons.
Accumulation Mode
Accumulation mode refers to a condition in a Metal-Oxide-Semiconductor (MOS) capacitor where the majority of charge carriers (either electrons or holes) from the semiconductor substrate accumulate near the surface. This accumulation occurs when an appropriately polarized potential, higher than the flat band potential, is applied between the gate and the body of the MOS capacitor. Accumulation mode is not commonly encountered in Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs).
Active-High Latch
An active-high latch is a latch circuit that becomes transparent or allows data to pass through when the clock input is in the high state (typically logic level 1).
Active-Low Latch
In contrast, an active-low latch is a latch circuit that becomes transparent or allows data to pass through when the clock input is in the low state (typically logic level 0).
Active Mask (Diffusion Mask)
An active mask, also known as a diffusion mask, is a photomask used in semiconductor fabrication. It defines areas on the semiconductor wafer where thin oxide layers are deposited or grown during the LOCOS (Local Oxidation of Silicon) process. Additionally, it defines regions under which the MOSFET gate will be fabricated. It is crucial for creating the desired transistor structures.
Active Region (Bipolar Junction Transistor – BJT)
The active region is a mode of operation for Bipolar Junction Transistors (BJTs). In this region, the base-emitter (BE) junction is forward-biased, while the base-collector (BC) junction is reverse-biased. BJTs operate in the active region when used in amplifiers. Here, a small base current controls a larger collector current, effectively turning the transistor into a current source. The collector is designed to efficiently collect most of the carrier flux from the emitter despite the reverse bias at the BC junction.
Address Change Detector
An address change detector is an electronic circuit used in memory systems. It generates a pulse or signal when there is a change in the address bus signals during a clock cycle. This detector typically involves XOR gates, OR gates, and flip-flops. It is used to trigger self-timed read operations in memories, eliminating the need for a dedicated read flag input.
Alignment
Alignment refers to the precise positioning and registration of a photomask (used in semiconductor lithography) relative to the semiconductor wafer. Proper alignment is crucial to ensure that patterns are accurately transferred onto the wafer. Misalignment can lead to defects in the semiconductor devices.
Alpha Grid
Alpha grid is a clock distribution technique in integrated circuits. It involves routing the clock signal through a dense grid of metal lines. This grid may receive clock inputs from multiple directions to reduce skew (timing differences). Alpha grids are designed to minimize absolute skew, but they can be area and power-intensive.
Amorphous Silicon
Amorphous silicon is a form of silicon that lacks a regular crystal structure. It may have very small or no crystal domains and can even be in a powdered form. Amorphous silicon possesses unpredictable and non-uniform electrical properties, making it unsuitable for semiconductor circuitry. However, it finds applications in technologies like amorphous silicon solar cells.
Annealing
Annealing is a heat treatment process used in semiconductor fabrication. It involves heating a silicon wafer to a high temperature, just below the silicon melting point. This process allows the atomic bonds in the silicon crystal structure to relax and reorganize. Proper annealing requires gradual cooling after heating to ensure the crystal structure stabilizes effectively.
Antenna Effect
The antenna effect is a phenomenon that can occur during semiconductor fabrication when connecting polysilicon gates to long metal lines. If these metal lines pass through multiple layers without proper connections, they can accumulate static charge. This charge can create a significant electric field, potentially leading to breakdowns in the thin oxide layers of transistors.
Antenna Rules
Antenna rules are specific design rules used in semiconductor manufacturing. They define limits on the ratio between the area covered by metal layers (except the topmost layer) and the area of a polysilicon gate in a connection. Adhering to these rules ensures that the antenna effect is minimized during the fabrication process.
Architecture (VHDL)
In VHDL (VHSIC Hardware Description Language), architecture is a crucial part of a design associated with an entity. An architecture provides a detailed description of the internal construction of a digital circuit. It includes architecture declarations (defining signals, types, subtypes, constants, and components) and an architecture body (describing how the circuit is constructed using instantiations, concurrent statements, sequential statements, and function calls).
Array (VHDL)
In VHDL, an array is a user-defined type where signals are organized into arrays of the same type. These arrays can also consist of vectors, effectively creating matrices of binary values. Arrays are valuable for managing large storage structures like shift registers or memories.
Array Multiplier
An array multiplier is a digital circuit used for binary multiplication. It employs AND gates to generate partial products and half adders or full adders to accumulate these partial products into the final result. Array multipliers often have long critical paths, and their design can significantly impact the critical path in pipelines where they are used.
ASIC (Application-Specific Integrated Circuit)
An ASIC is an integrated circuit designed to perform specific functions as required by the user or application. ASICs are often developed using standard cell libraries and are tailored to meet specific application requirements, making them highly efficient for dedicated tasks.
Assert (VHDL)
In VHDL, the assert statement is used for simulation and verification purposes. It can be applied both concurrently and sequentially. The assert statement checks a specified condition, and if the condition is true, it generates a report with a designated string message and assigns a severity level to that message.
Astable Circuit
An astable circuit is an electronic circuit configuration where neither of its logic outputs (high or low) remains stable. Instead, it continuously oscillates between both logic states, without maintaining either state for an extended period. A common example is a ring oscillator composed of an odd number of inverters connected in a feedback loop.
Asynchronous Reset
An asynchronous reset is a reset signal in digital circuits that takes higher priority than the clock signal. It can override the clock signal to immediately reset the circuit. Asynchronous resets are considered good design practice for registers, as they ensure a known initial state and the ability to recover from unexpected conditions.
Asynchronous FIFO
An asynchronous FIFO (First-In-First-Out) is a type of memory buffer with two independent ports, each operating on its clock domain. One port is for writing data, and the other is for reading data. Asynchronous FIFOs are used to facilitate data synchronization in systems with different clock domains. Synchronizers are required to ensure the proper functioning of empty and full flags, which prevent overflow and underflow.
Attribute (VHDL)
In VHDL, an attribute is a tool that allows designers to extract information about a named item within a design. These items can include types, signals, files, variables, functions, or components. Attributes are valuable for experienced designers to enhance portability, elegance, and efficiency in designs. Users can also define custom attributes to attach special characteristics to design elements.
Automatic Test Equipment (ATE)
ATE is a hardware setup used to automatically test and evaluate electronic circuits, particularly packaged microchips. These systems are employed in commercial settings to efficiently assess a large volume of chips. ATE typically includes a chip mounting setup, robotic arms for automated loading and unloading, and a computer to apply tests, collect observations, and make pass/fail decisions. Binning is the process of categorizing each chip based on its performance.
Automatic Test Pattern Generation (ATPG)
ATPG is the process of automatically generating test patterns for testing a digital circuit. This is often associated with Built-In Self-Test (BIST) methodologies. ATPG methods can employ techniques like linear feedback shift registers to produce test patterns.
