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RTL is the earliest class of transistorized digital logic circuit; it was succeeded by diode–transistor logic (DTL) and transistor–transistor logic (TTL). RTL circuits were first constructed with discrete components, but in 1961 it became the first digital logic family to be produced as a monolithic integrated circuit.
A logic family of monolithic digital integrated circuit devices is a group of electronic logic gates constructed using one of several different designs, usually with compatible logic levels and power supply characteristics within a family. Many logic families were produced as individual components, each containing one or a few related basic ...
The simplest family of logic gates uses bipolar transistors, and is called resistor–transistor logic (RTL). Unlike simple diode logic gates (which do not have a gain element), RTL gates can be cascaded indefinitely to produce more complex logic functions. RTL gates were used in early integrated circuits.
Current mode logic (CML), or source-coupled logic (SCL), is a digital design style used both for logic gates and for board-level digital signaling of digital data. The basic principle of CML is that current from a constant current generator is steered between two alternate paths depending on whether a logic zero or logic one is being represented.
Combinational logic performs all the logical functions in the circuit and it typically consists of logic gates. For example, a very simple synchronous circuit is shown in the figure. The inverter is connected from the output, Q, of a register to the register's input, D, to create a circuit that changes its state on each rising edge of the clock ...
The first semiconductor logic family was resistor–transistor logic. This was a thousand times more reliable than tubes, ran cooler, and used less power, but had a very low fan-out of 3. Diode–transistor logic improved the fan-out up to about 7, and reduced the power. Some DTL designs used two power supplies with alternating layers of NPN ...
Examples of these include multipliers, generic DSP blocks, embedded processors, high-speed I/O logic and embedded memories. Higher-end FPGAs can contain high-speed multi-gigabit transceivers and hard IP cores such as processor cores , Ethernet medium access control units , PCI or PCI Express controllers, and external memory controllers .
The user may use a variety of languages and tools to create this description. Examples include a C/C++ model, VHDL, SystemC, SystemVerilog Transaction Level Models, Simulink, and MATLAB. RTL design: This step converts the user specification (what the user wants the chip to do) into a register transfer level (RTL) description. The RTL describes ...