Digital CMOS Abbreviation T Alphabet Dictionary
Technology Scaling
Technology scaling refers to the process of reducing the dimensions and scaling down the physical size of integrated circuits as semiconductor technology advances. This scaling involves shrinking all circuit dimensions, including transistor sizes and interconnects. Technology scaling helps reduce chip area and power consumption but requires careful management of parameters to maintain noise margins and prevent dielectric breakdown.
Test (Test Vector)
In the context of hardware testing, a test, often referred to as a test vector, is a specific input applied to a unit under test (UUT) during the testing process. By applying known input patterns and comparing the observed output to expected results, testing aims to verify the functionality and correctness of the UUT. Test vectors help identify defects and ensure the UUT operates as intended.
Testbench
A testbench is a specialized design in VHDL (VHSIC Hardware Description Language) used for testing and verifying digital circuits. It typically consists of an empty entity and an associated architecture that serves as a testing environment for a specific unit under test (UUT). The testbench includes processes for inputting test vectors, applying them to the UUT, and assessing the results. Testbenches play a crucial role in verifying the functionality and correctness of digital designs.
Testbench, Hardware
A hardware testbench is a specialized testing environment that operates on a hardware platform, often an FPGA (Field-Programmable Gate Array). Unlike regular software-based testbenches, hardware testbenches are designed for speed and direct interaction with the hardware under test. They must have defined ports to facilitate the loading and unloading of tests and cannot contain constructs that are not synthesizable for direct implementation on the hardware platform.
Testing
Testing is the systematic process of applying predefined tests to a unit under test (UUT) to evaluate its functionality and detect any faults or defects. The testing process involves providing inputs to the UUT, observing its responses, comparing those responses to expected results (a gold standard), and making judgments about the UUT’s fault-free operation. The effectiveness of testing depends on the controllability of input nodes within the internal subsystems of the UUT.
Thermal Equilibrium
Thermal equilibrium is a state in which a material reaches a balanced condition with regard to charge concentrations, governed by the mass-action law. In thermal equilibrium, there is a single Fermi level that controls charge concentration. This state is achieved when there are no external voltage sources, no net current flow, no injection of carriers, and no changes in operating temperature. It’s important to note that thermal equilibrium doesn’t exclude the presence of built-in fields, potentials, band bending, or the flow of certain current components.
Thermal Speed
Thermal speed refers to the high-speed random motion of charge carriers (electrons or holes) within a material due to thermal energy. Despite the significant magnitude of thermal velocity, it does not contribute to net current flow because its mean velocity is zero. However, in highly scaled transistors, thermal velocity is a fundamental factor in defining current behavior, particularly in phenomena like velocity overshoot and tunneling.
Thin Body Transistor
A thin body transistor is a type of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) architecture that is often built on insulating substrates. In this design, the body of the transistor is a thin region of silicon isolated above an insulator, as opposed to the traditional bulk silicon substrate. Thin body transistors help reduce certain undesirable effects, such as drain-induced barrier lowering. However, they require careful doping and design to maintain well-defined body potentials.
Thin Oxide, TOX
TOX refers to the thin oxide layer formed beneath the gates of transistors. It also extends over the source and drain diffusion regions and well/substrate contacts. TOX signifies all areas where the actual transistor exists, in contrast to the thick, insulating field oxide typically used in a LOCOS (Local Oxidation of Silicon) process.
Threshold Voltage
The threshold voltage of a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is the voltage level at which strong inversion (i.e., significant channel current) sets in. Below the threshold voltage, the MOSFET is considered to be in the cutoff state, meaning it is off. It’s important to note that even below the threshold voltage, there is a weak inversion layer, but it is not sufficient to drive significant current. The threshold voltage is defined as the gate potential at which the inversion carrier concentration at the silicon surface matches the opposite carrier concentration in the bulk substrate.
Time-Constant
In a circuit that consists of a single resistor and a single capacitor, the time-constant is the product of the resistance and capacitance values. This time constant represents how quickly the RC circuit will charge or discharge. It is often used in linear approximations for delay calculations, providing an estimate of the time it takes for the circuit to reach a specific voltage or charge level.
Time-Dependent Dielectric Breakdown
Time-dependent dielectric breakdown (TDDB) is a phenomenon that occurs as a transistor age and is used more frequently. It results in the oxide layer of the transistor becoming more porous and exhibiting increased conductivity over time. The exact causes of TDDB are not fully understood, and it is poorly characterized. However, TDDB can lead to increased leakage current through gate tunneling and is a significant factor affecting the reliability of deeply scaled transistors.
Time of Flight
Time of flight refers to the time it takes for a signal to travel through the length of a transmission line. It is a function of the speed of light in the medium of the transmission line material. When dealing with transmission lines, it’s essential to consider the time of flight because it provides an estimate of the signal delay. In situations where there is the possibility of signal reflections, the actual delay can be significantly higher than the time of flight.
Total Effort
In the context of a logic gate, the total effort represents the combined effort exerted by the gate to drive its output. It is calculated as the product of the logical effort (which accounts for the gate’s internal complexity) and the fan-out (the number of loads the gate must drive). The total effort helps determine the ability of the gate to drive external loads while overcoming its own inherent complexity.
Transaction
A transaction refers to a scheduled change in the value of a signal. When a signal assignment statement is encountered within a process, it leads to a scheduled change in the signal’s value. However, this change does not become an actual event until the end of the process (if there is a sensitivity list) or the first subsequent wait statement is encountered. Transactions help manage signal changes within a process and ensure proper sequencing of events.
Transistor
A transistor is an electronic device with at least three terminals, where the flow of current between two of the terminals is controlled by the voltage applied to a third terminal. Transistors are fundamental components in electronic circuits and are widely used for amplification, switching, and signal processing. In many transistors, such as Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), additional terminals are present but are not directly involved in the core transistor action.
Transition Fault
A transition fault is a type of logic fault, typically associated with memory circuits rather than general logic. Transition faults occur when a memory cell fails to make a certain transition between logic states. Unlike stuck-at faults, where a cell is stuck at a specific logic value (0 or 1), transition faults indicate that the cell can take either logic value but fails to transition in one of the two directions.
Transmission Gates
Transmission gates are electronic switches used in digital circuits. They are constructed using complementary metal-oxide-semiconductor (CMOS) transistors, consisting of both an NMOS (n-type metal-oxide-semiconductor) and a PMOS (p-type metal-oxide-semiconductor) transistor connected in parallel. The operation of a transmission gate requires logic complementary inputs to control both transistors simultaneously. It allows signals, either “1” or “0,” to pass through the switch, making it a versatile component for signal routing and level shifting.
Truncation
Truncation refers to the process of discarding or removing bits from a fixed-point register or data representation. This is done to reduce the size of data and can be useful for conserving memory or simplifying subsequent operations. However, truncation introduces quantization error, which is the difference between the original value and the truncated value, and must be considered in applications where precision is critical.
Tunneling
Tunneling is a quantum mechanical phenomenon where particles, such as electrons, can pass through energy barriers that would be classically insurmountable. In the context of electronics, electron tunneling is a mechanism that can result in the flow of tunneling current. It occurs because electrons exhibit both particle and wave-like behavior. When an electron’s wave function extends beyond an energy barrier, there is a finite probability that it can pass through the barrier, even if its energy is lower than the barrier height.
Type (VHDL)
In VHDL (VHSIC Hardware Description Language), “type” refers to a user-defined data type. VHDL allows designers to create custom data types to suit their specific design needs. Common types in VHDL include enumerations, which define a set of named values, and arrays, which allow the organization of data into indexed collections. Custom types provide flexibility in specifying the data structures used in digital designs.
Typical Corner
In the context of CMOS (Complementary Metal-Oxide-Semiconductor) fabrication and design, a “typical corner” refers to a set of operating conditions in which both NMOS and PMOS transistors perform as expected. It represents a scenario where the semiconductor manufacturing process meets the design’s anticipated requirements. Designing for the typical corner ensures that the chip is likely to function correctly under these standard conditions.
