Electrical4U 
A Kelvin Bridge (Kelvin double bridge) measures low resistance by adding extra ratio arms so lead and contact resistance do not swamp the unknown. A Wheatstone bridge is the usual tool for medium resistance; a well-built one can reach about 0.1% on those values, not on milliohm samples. Textbooks group electrical resistance into three bands … Read more
Excess 3 Code This page is about BCD addition and subtraction with Excess 3 code. Excess 3 code stores each decimal digit as the 4-bit binary of that digit plus 3 (0 is 0011, 9 is 1100). For any binary number already grouped as BCD digits, add 0011 to each group to form Excess-3, then … Read more
Error detection and correction codes add extra bits so a receiver can see whether a digital word was changed in transit, and in some codes restore the original bits. Analog and digital links both pick up errors; a computer or a comms link needs a definite check because one wrong bit can change a code. … Read more
Fan-out in digital electronics is the number of same-family gate inputs that one logic-gate output can drive without leaving the valid logic levels. One output can feed several inputs, but only up to that count.The limit is set by how much current the output can source at a high level and how much current it … Read more
TTL means Transistor Transistor Logic, a bipolar digital family built from NPN transistors, PN junction diodes and diffused resistors. The usual gate is a NAND gate. Subfamilies include standard 74, low-power 74L, high-power 74H, Schottky 74S plus later LS, ALS and 74F parts. The sections below cover the inner circuit of the main groups. Standard … Read more
A logic gate is a digital circuit whose output follows a Boolean function of its inputs. Earlier pages covered the internals of digital logic gates. This page covers common applications of logic gates that follow from that truth table. OR combines trips. AND acts as an enable or inhibit. XOR and XNOR handle parity. NOT … Read more
A Schmitt Gates device is a logic gate whose input uses two trip points instead of one. Ordinary gates switch at a single threshold voltage for both rising and falling edges, somewhere between a valid low and a valid high. A slow or noisy edge that lingers near that one trip point can make the … Read more
SSI and MSI chips still ship logic gates, flip flops, counters, multiplexers and demultiplexers. Those parts sit at small-scale and medium-scale integration. TTL and ECL used too much area and power for early MOS-scale LSI. CMOS later became the VLSI family. In the MOS-LSI years the dense options were PMOS, NMOS and bipolar I2L. This … Read more
A digital integrated circuits logic family is one production style and circuit style that a vendor publishes as a matched set. Parts in that Logic Families group share the same electrical envelope, so one family of ICs can usually plug together without a translator. The shared spec covers supply voltage range, speed class, power, input … Read more
Earlier pages covered the usual gates in digital electronics: the basic AND gate, OR gate and NOT gates, plus NAND, NOR, XOR and XNOR. An INHIBIT gate adds a control pin that can freeze the output. Designers use that pin when a path must stay quiet unless a separate enable is true.The inhibit pin, when … Read more