Search results
Results From The WOW.Com Content Network
A logic circuit diagram for a 4-bit carry lookahead binary adder design using only the AND, OR, and XOR logic gates.. A logic gate is a device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output.
XOR has the worst-case Karnaugh map—if implemented from simple gates, it requires more transistors than any other function. Back when transistors were more expensive, designers of the Z80 and many other chips were motivated to save a few transistors by implementing the XOR using pass-transistor logic rather than simple gates. [4]
Schematic of basic two-input DTL NAND gate. R3, R4 and V− shift the positive output voltage of the input DL stage below the ground (to cut off the transistor at low input voltage). Diode–transistor logic (DTL) is a class of digital circuits that is the direct ancestor of transistor–transistor logic.
If any of the logic gates becomes logic low (transistor conducting), the combined output will be low. Examples of this type of gate are the 7401 [15] and 7403 [16] series. Open-collector outputs of some gates have a higher maximum voltage, such as 15 V for the 7426, [17] useful when driving non-TTL loads.
Diode–transistor logic (DTL) was used in the IBM 608 which was the first all-transistorized computer. Early transistorized computers were implemented using discrete transistors, resistors, diodes and capacitors. The first diode–transistor logic family of integrated circuits was introduced by Signetics in 1962.
If a diode–transistor logic gate drives a transistor inverter of similar construction, the transistor will have a similar base-collector capacitance that is amplified by the transistor gain, so that it will be too slow to pass the glitch. But when the diode is much slower, recovery will become a concern:
The R-pulled circuit acts like a NOR gate that sinks OUT to the GND. As an example, here is a NOR gate implemented in schematic NMOS. If either input A or input B is high (logic 1, = True), the respective MOS transistor acts as a very low resistance between the output and the negative supply, forcing the output to be low (logic 0, = False).
An AOI21 logic gate in CMOS using a complex gate (left) and standard gates (right) AND-OR-invert (AOI) and OAI gates can be readily implemented in CMOS circuitry. AOI gates are particularly advantaged in that the total number of transistors (or gates) is less than if the AND, NOT, and OR functions were implemented separately.