Digital CMOS Abbreviation C Alphabet Dictionary
Carry Bit
In an adder circuit, the carry bit is an output bit generated in a one-bit position that serves as an input to the next bit position during binary addition. The logic for generating the carry bit is relatively simple, involving an AND gate for half adders and a more complex sum-of-products logic for full adders. In an N-bit binary adder, except for the last bit position, the carry bit from each position becomes part of the overall adder output and feeds into the next bit position.
Carry-Bypass Adder
A carry-bypass adder is a type of N-bit adder designed for speed. It divides the adder into smaller blocks, and within each block, the carry chain can bypass the entire block if all locations within the block are propagating the carry signal. This can improve the critical path delay of the adder by reducing the slope of linear growth compared to traditional ripple-carry adders.
Case (VHDL)
In VHDL (VHSIC Hardware Description Language), “case” is a conditional statement construct used within a process. Its syntax is similar to that of programming languages. Case statements are used to create multiplexers and prioritize different choices based on conditions. They are particularly useful when dealing with a large number of possible choices.
Cell (Memory)
In memory design, a cell is the smallest building block capable of storing a single bit of data. Cells exist at the intersections of word lines and bit-lines within a memory array. Regardless of the specific data they store, each intersection of a word-line and bit-line is considered a cell. Memory cells must be designed to be small to maximize memory density, but they must also be able to drive the significant capacitance of bit-lines, which can create a design challenge.
Cell Delay Replica
A cell delay replica is a dummy circuit designed to replicate the delay characteristics of the actual cell that drives a bit-line in self-timed memories. While the construction of the replica doesn’t need to be identical to the actual cell, it should mimic its delay. This replica is used to delay the sense amplifier and enable signal in self-timed memory circuits.
Chain Fan-Out
Chain fan-out is a term used to describe the ratio between the output capacitive load that a chain of logic gates drives and the input capacitance of the first stage in that chain. It represents the fan-out of the entire chain when considered as a single “black box.”
Chain Logical Effort
In a chain of logic gates, chain logical effort is the product of the individual logical efforts of the gates within the chain. It quantifies the overall difficulty of driving the complexity of the logic within the chain relative to a chain of inverters.
Chain Total Effort
Chain total effort is the total effort expended across an entire logic chain. It is calculated as the product of the individual stage fan-outs and stage logical efforts. Additionally, it can be expressed as the product of the chain logical effort and the chain fan-out.
Channel Length
Channel length in a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) refers to the length of the MOSFET’s channel, which is the shortest distance between the source and drain terminals beneath the gate. Channel length plays a critical role in controlling current flow and resistance within the transistor.
Channel Length Modulation
Channel length modulation is a secondary effect that affects MOSFETs, particularly in short-channel transistors. It results in the saturation current becoming a weak function of the drain potential. Channel length modulation has various physical causes, including finite depletion region resistance, ballistic transport, and tunneling.
Channel Width
Channel width in a MOSFET refers to the depth or width of the channel region. A wider channel allows the MOSFET to carry more current and reduces its resistance. It is also related to the width of the top plate of the MOS capacitor.
Characteristic Impedance
In the context of electrical transmission lines, characteristic impedance represents the ratio of voltage to current for a single wave traveling through the transmission line. In VLSI (Large-scale integration) design, this value is significant because it defines the impedance to which the source of a large wire must be matched to prevent source-side reflections.
Charge Carrier
A charge carrier is a charged particle, such as an electron or hole, that can move under the influence of an electric field or a concentration gradient. In semiconductor materials, electrons and holes are the primary charge carriers responsible for carrying electric current.
Charge Conservation
In a closed system of capacitors, charge conservation ensures that the total charge on the upper plates of the capacitors remains constant, regardless of how the capacitors are reconfigured or connected. This principle is vital for understanding the behavior of capacitive circuits.
Charge Sharing
In a closed system of capacitors, the principle of charge conservation dictates that the total charge remains constant when capacitors are reconfigured or connected differently. Charge sharing refers to the redistribution of charge among these capacitors to satisfy the new connections while maintaining charge conservation.
Circuit Under Test
The circuit under test (CUT) refers to the specific electronic circuit, sub-circuit, system, subsystem, or unit being examined or evaluated within a testing setup. It can range from an entire microchip or assembled printed circuit board (PCB) in automated testing to a core component within a chip during built-in self-test (BIST) or even a high-level hardware description language (HDL) construct during verification.
Clean Room
A clean room is a controlled environment designed to minimize the presence of airborne particles. This control is achieved by introducing highly filtered and purified air and ensuring rapid air exchange rates. Clean rooms are vital in semiconductor fabrication facilities to prevent particle contamination during the manufacturing process. Different levels of cleanliness may be required for various semiconductor manufacturing steps.
Clock
In digital circuits, a clock is a periodic signal with a specific frequency used to synchronize and time various events within a synchronous circuit. It plays a crucial role in controlling the timing of memory cycles, and enabling and disabling registers, latches, and dynamic logic. Although it’s often visualized as a square wave, in reality, it resembles a periodic waveform, such as a sine wave.
Clock Domain
A clock domain represents a subsystem or group of circuits within a digital design that operates based on a specific clock signal. Circuits within the same clock domain are considered synchronous with respect to that clock. Moving data between different clock domains requires synchronization techniques to avoid timing violations.
Clock Jitter
Clock jitter is a phenomenon where the phase of a clock signal varies slightly from one clock cycle to the next. It is a form of phase noise and can result from variations in clock generation or clock distribution. Clock jitter introduces uncertainty in the timing of digital signals and can limit the frequency at which a circuit can operate reliably.
Clock Network
A clock network is a set of interconnected wires and buffers used to distribute a clock signal to all registers and logic gates within a synchronous digital circuit. Clock networks are designed to minimize area, reduce skew, manage power consumption, and enhance flexibility in modifying clock signals.
Clock Overlaps
Clock overlaps occur due to the delay between a clock signal (denoted as “clock”) and its complement (denoted as “clock'”). During these periods, both clock and clock’ have identical values. These overlaps can lead to signal-clock racing issues if not properly managed. Clock overlaps are crucial considerations when imposing hold-time requirements on signals.
Clock Skew
Clock skew is the phenomenon where the clock observed at different registers within a synchronous circuit has different phases or arrival times. Clock skew can occur due to variations in wire lengths, buffer delays, and load mismatches. It can impact setup and hold-time requirements and needs careful management.
Clock Spine
A clock spine is a line of buffers that distribute a clock signal along a single dimension. Spines can achieve minimal skew within that dimension but are typically used in combination with other clock distribution methods to cover the entire circuit.
Clock Tree
A clock tree is a method of clock distribution where a clock signal is driven across a tree-like structure with multiple branches. Clock trees aim to reduce relative skew, especially between registers at different levels of the tree. However, they are closely tied to the overall chip design, making modifications challenging.
Clustered Defects
Clustered defects are defects in a semiconductor wafer that are concentrated within a specific area or region. These defects often indicate systematic issues in the fabrication process. While they may not have as significant an impact on yield as randomly distributed defects, they can still affect chip performance.
CMOS (Complementary Metal-Oxide Semiconductor)
CMOS is a widely used digital logic family characterized by complementary connections of metal-oxide-semiconductor transistors. CMOS gates feature both NMOS (n-channel MOS) and PMOS (p-channel MOS) transistors in equal numbers and exhibit characteristics like excellent noise margins, signal integrity, and low steady-state static power consumption. However, they can have challenges with area efficiency and delay performance.
CMP (Chemical-Mechanical Polishing)
CMP is a semiconductor manufacturing process used to achieve an extremely even and flat surface on a semiconductor wafer. It combines chemical and mechanical techniques to polish the surface. Abrasive and corrosive materials are applied, while simultaneous shaking, vibration, and rotation are used to facilitate the polishing. CMP is essential in modern semiconductor processes to maintain flatness between successive metallization layers. It’s often kept separate from the main CMOS process due to its potentially contaminating nature.
Collector
In a bipolar junction transistor (BJT), the collector is one of the two peripheral regions. It’s typically more lightly doped and is n-type in an npn BJT or p-type in a pnp BJT. The collector’s main purpose is to provide a large area for the collection of injected carriers from the emitter. In the active region of BJT operation, the collector current should approximately track the emitter current.
Column Decoder
In memory devices, a column decoder is a multiplexer that selects one specific bit-line out of all the columns in the memory bank. It typically receives a portion of the address bus as select lines to determine which bit-line to activate. In read/write memories, column decoders can also act as demultiplexers to direct data from the data-in bus to the appropriate bit-line for writing.
Column Driver (Memories)
Specifically used in RAMs (Random Access Memories), a column driver is a substantial buffer located at the end of each column. These drivers are responsible for driving the voltage levels on the bit-lines to certain values, enabling data to be written into the memory cells. Column buffers are often constructed using chains of inverters sized using logical effort analysis.
Combinational Logic
Combinational logic refers to a type of digital logic circuit where the output is determined solely by the current values of its inputs. The output changes immediately in response to any change in input values, and there are no internal memory elements such as flip-flops. The logic function performed is unconditional, meaning it operates based solely on the present input values.
Combinational Logic Block
This block consists entirely of combinational logic components. In a pipeline structure, a combinational logic block is typically positioned between two registers. The block’s performance is characterized by its best and worst-case delay times.
Common Base Current Gain
This is the ratio of the collector current to the emitter current in a BJT operating in the common base configuration. It accounts for the portion of emitter current that is wasted as base current.
Common Emitter Current Gain
This gain represents the ratio of the collector current to the base current in a BJT operating in the common emitter configuration. It is typically high and is often referred to as the current gain of a transistor.
Component (VHDL)
In VHDL (VHSIC Hardware Description Language), a component is a construct used for hierarchical design. It informs the entity where it is declared that instances of this component can be declared within the architecture. It does not specify the number of instances or their connections; rather, it serves as a template for instantiation.
Concurrent Statements
These are statements in a hardware description language (HDL) or VHDL that are executed in parallel. The order of these statements doesn’t affect the result, and they are ideal for describing hardware setups. This reflects the foundational philosophy of HDL syntax, which is well-suited for describing hardware.
Conduction Band
The conduction band is the energy band in a solid material that represents the lowest energy levels that are unoccupied at absolute zero temperature (0 K). At higher temperatures, it may contain conduction electrons, depending on the bandgap of the material.
Conduction Band Edge
This is the lowest energy level within the conduction band. Electrons, when left to their natural behavior, tend to occupy this level if it’s available. The energy difference between the Fermi level and the conduction band edge provides insight into the concentration of conduction electrons.
Configuration (VHDL)
In VHDL, configurations are constructs used to manipulate entities in preparation for instantiation. They serve two main purposes: associating instances with specific architecture-entity bindings and renaming entity ports before instantiation. Configurations are particularly useful in large designs or when multiple teams collaborate on a design.
Constant (VHDL)
In VHDL, a constant is a named item that holds a specific value of a particular data type. Constants can be derived from other constant values through function calls, as long as these derivations can be resolved during synthesis. Constants are declared within the architecture.
Contact Exposure
Contact exposure is a classical mechanism used in photolithography where the photomask physically contacts the wafer surface during the exposure process. This method helps avoid optical artifacts but can lead to the wear and tear of the masks. Features on the mask must directly correspond to features on the wafer.
Contact Mask
This is a photomask used in semiconductor manufacturing to define contact or vertical hole patterns between the active layer (where transistors are formed) and either the poly (polysilicon) layer or Metal1 (the first metal layer). Contact masks are crucial for creating electrical connections between different layers of a semiconductor device.
Controllability (Testing)
In the context of testing electronic circuits, controllability refers to the ability to set and control the state of an internal node within the circuit. This is important for applying test vectors and ensuring that specific parts of the circuit can be effectively tested. Achieving high controllability often involves providing access to internal nodes through input ports or pins, although managing the number of required pins can be a challenge.
Controller
In a circuit, a controller is a section responsible for sequencing and providing intelligence to the system. It typically doesn’t contain signal processing circuits but plays a crucial role in governing the behavior of the circuit.
Copper Trace (PCB)
On a printed circuit board (PCB), a copper trace refers to a wide copper conductor etched onto the board’s surface. These traces are used to interconnect various components mounted on the PCB. Copper traces are significantly larger than the internal wiring within semiconductor dies and can introduce an asymmetric capacitive load, requiring careful design of output pins and interfacing.
Counter
A counter is a sequential digital circuit used to count in a specific sequence. Counters are valuable for establishing control and sequencing within a circuit. They can be configured to count up, count down, or both (up/down). Some counters, like Gray-encoded counters, can count in arbitrary sequences.
Coupling Fault
This type of fault, often associated with memory circuits, can be complex and challenging to test for. Coupling faults involve interactions between memory cells where the value of one cell is influenced by the values of its neighboring cells. Different types of coupling faults include bridge faults, inversion faults, and idempotent faults.
Critical Dimension
The critical dimension is the smallest dimension that can be reliably achieved using a particular photolithography exposure method. It depends on factors like the wavelength of light used, numerical aperture, and the medium in which the projection occurs. Achieving smaller critical dimensions is a key goal in semiconductor manufacturing.
Critical Field
This field represents the point at which a charge carrier, such as an electron, reaches its saturation velocity. The critical field is a constant value associated with a particular technology and influences the saturation drain potential, which depends on the channel length.
Critical Path
In a synchronous pipeline or digital circuit, the critical path is the path with the longest combinational delay between two registers. It determines the maximum operating frequency of the circuit and plays a crucial role in placement and routing decisions.
Crowbar Current
Crowbar current is the current that flows from the power supply to the drain of a gate, typically a CMOS gate, during switching. It occurs due to the finite slope of input signals, causing transistors in the pull-down network (PDN) and pull-up network (PUN) to be active simultaneously. This current can negatively impact delay and power consumption, especially in static CMOS circuits and with short-channel devices.
Current
Current refers to the flow of electric charge carriers, such as electrons or holes, through a conductive pathway. Current can flow due to the presence of an electric field or in response to a concentration gradient.
Custom Attributes
Custom attributes, also known as user-defined attributes, are attributes defined by the user and attached to named items within a design. These attributes are often used in commercial design settings to convey tool or design-related information.
Cutoff Region (BJT)
In a Bipolar Junction Transistor (BJT), the cutoff region is one of the operational regions where both the emitter-base and collector-base junctions are reverse-biased. In this region, essentially no primary current flows through any terminal of the device, although some leakage currents may still exist. This region is commonly used as the “off” state in bipolar logic.
Cutoff Region (MOSFET)
In a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), the cutoff region is an operational state where a conducting channel does not exist between the source and drain terminals. Consequently, no primary current flows between the source and drain, making it useful as an “off” state in logic gates.
CVD (Chemical Vapor Deposition)
CVD is a deposition process used in semiconductor manufacturing, where two materials react over a substrate to form a film. This film is created by depositing material in a gaseous state onto the substrate surface. CVD typically requires heat as a catalyst and may produce toxic byproducts. It is often used to deposit materials like polysilicon or silicon dioxide on semiconductor surfaces.
Czochralsky Process
The Czochralsky process is a widely used method for producing high-quality silicon ingots for semiconductor wafers. It involves melting high-purity silicon and adding appropriate dopants. A small seed crystal is then lowered into the molten silicon, and as it’s raised while rotating, it allows a single crystal to grow aligned with the seed, forming an elongated ingot. This process is essential for obtaining high-quality silicon material used in semiconductor manufacturing
