Logic decoders and logic demultiplexers are integrated circuits (ICs) that move data between inputs and outputs. Logic decoders convert coded information into a familiar or uncoded form so that, for example, binary coded decimal (BCD) numbers can be converted into digits that display on a seven-segment calculator. Logic demultiplexers switch digital data from one input line to several output lines in a specific time sequence. They are often used in telecommunications applications. Logic decoders and logic demultiplexers are available with 1 to 4 input lines and 2, 4, 6, 8, 10, 14, or 16 output lines. Both types of devices have inverted outputs so that the selected output is set to 0, while all of the other outputs remain at 1. Logic decoders can be used individually, or connected together for use as demultiplexers.
Logic decoders and logic demultiplexers vary in terms of supply voltage, operating current, propagation delay, and power dissipation. Supply voltages range from - 5 V to 5 V and include intermediate voltages such as -4.5 V, -3.3 V, -3 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3 V, 3.3 V, and 3.6 V. The operating current is the minimum current needed for active operation. The propagation delay is the time interval between the application of an input signal and the occurrence of the corresponding output. Power dissipation, the total power consumption of the device, is generally expressed in watts or milliwatts. Some logic decoders and logic demultiplexers are radiation hardened or tolerant. Others include circuitry for protection against electrostatic discharge (ESD).
Selecting logic decoders and logic demultiplexers requires an analysis of logic families. Transistor-transistor logic (TTL) and related technologies such as Fairchild advanced Schottky TTL (FAST) use transistors as digital switches. By contrast, emitter coupled logic (ECL) uses transistors to steer current through gates that compute logical functions. Another logic family, complementary metal-oxide semiconductor (CMOS), uses a combination of p-type and n-type metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. Logic families for logic decoders and logic demultiplexers include cross-bar switch technology (CBT), Gallium arsenide (GaAs), integrated injection logic (I2L) and silicon on sapphire (SOS). Gunning with transceiver logic (GTL) and gunning with transceiver logic plus (GTLP) are also available.
Logic decoders and logic demultiplexers are available in a variety of IC package types and with different numbers of pins and flip-flops. Basic IC package types include ball grid array (BGA), quad flat package (QFP), single in-line package (SIP), and dual in-line package (DIP). Many packaging variants are available. For example, BGA variants include plastic-ball grid array (PBGA) and tape-ball grid array (TBGA). QFP variants include low-profile quad flat package (LQFP) and thin quad flat package (TQFP). DIPs are available in either ceramic (CDIP) or plastic (PDIP). Other IC package types include small outline package (SOP), thin small outline package (TSOP), and shrink small outline package (SSOP).