Logic family

Logic family called in digital technology, a number of blocks ( usually referred to as Integrated Circuits ), provide the basic ( such as logic gates) and usually more complex logic circuits available. The building blocks of a family are crafted with the same manufacturing process, use the same circuit technology, have similar electrical and mechanical properties and can therefore be combined easily.

The term logic family is used in a broader sense, often to refer to a circuit technique. However, a mere compliance of the circuit technology used does not guarantee that two circuits must be compatible.

  • 2.1 First Logic ( RTL / DTL )
  • 2.2 transistor-transistor logic (TTL)
  • 2.3 CMOS


74er series

The logic blocks today most commonly used are from the so-called '74 - series whose model number starts with 74 (see photo right). The subsequent combination of numbers identifying the logic function of the circuit 00 in this example means that it is a NAND device. Later, other logic families have been developed that differ in the manufacturing technique and the voltage levels being used ( and further, below), but not in the logic function. To distinguish these families from the original, you add a letter between the 74 and the " function number ". For example, a produced in low-power Schottky technology NAND gate is labeled 74LS00.

Often, the manufacturer uses two letters before the prefix, such as ' SN ' for Texas Instruments or 'MC' for Motorola (now ON Semiconductor Corp. ). ICs from different manufacturers may differ in other data (eg the maximum clock frequency ), they are therefore not always readily interchangeable.

From a possibly additionally printed on the IC package number, the date of manufacture can be derived, in this case the 45th week of the year 1976.

All modules in this series as well as all successors rows are delivered in DIP packages, nowadays optionally also in SMD version of it.

54er and 84er series

The components of the above-described 74er series is also available in versions for extended temperature ranges.

4000 series

The 4000 Series is a CMOS logic family. It is now rarely used. Many commonly used components, such as the PLL chip 4046 were also transferred to the '74 series. The name is then, for example 74HCT4046.

Emergence of logic families

First Logic ( RTL / DTL )

The first actual logic family was resistor - transistor logic, usually short RTL ( for eng. Resistor transistor logic ) called. These integrated circuits consist exclusively of resistors and transistors, the logic operations can be achieved by means of series or parallel connection of transistors. RTL is a circuit technique that manufacturers have made ​​different proprietary device families.

The diode transistor logic (DTL ) the logical connections on the input side via diodes produced and then amplified by a transistor stage and inverted. DTL is also to be understood as circuit technology with incompatible series. The slow fail-safe logic ( LSL) is a variant of DTL.

RTL and DTL are now only of historical interest.

Transistor - transistor logic (TTL)

The transistor-transistor logic (TTL ), the diode network to the inputs replaced by transistors having a plurality of emitter terminals. Although initially a number of semiconductor manufacturers own logic families had made ​​in TTL circuitry, the TTL family from Texas Instruments soon put through an industry standard. The remaining manufacturers abandoned their proprietary series and produced TTL circuits with the same specifications as Texas Instruments.

The numbering of Texas Instruments has prevailed: The first component of the series, consisting of four NAND gates with two inputs, called SN7400, at the following number has been incremented. Other manufacturers simply replace the prefix SN by its own letter sequences, such as DM7400 National Semiconductor. 7400 or '00 it was short for generic (vendor independent ) term for four NAND gates in TTL technology. ( See also: 74xx )

This TTL logic family was quickly extended by variants that were optimized for low power consumption and high switching speed and low-power TTL or are called high-speed TTL. From the model numbers 74L00 74H00 and the family designations L -TTL and TTL - H or 74L and 74H have shown. The original 7400 logic family is often called standard TTL, to distinguish them from the modified TTL families and the general term TTL ( within the meaning of TTL circuit technology).


Logical circuits can be designed not only with bipolar transistors, but also with field effect transistors (more precisely, MOSFETs ) can be realized. The first MOSFET circuit techniques have been known and used only PMOS and NMOS p -channel MOSFET or N- channel MOSFET. PMOS or NMOS circuit technology has been used, although for many digital circuits such as microprocessors, but no actual logic families originated.

CMOS ( for Complementary MOS) is a development of the PMOS and NMOS, and a complementary circuit is used, i.e. n-and p -channel MOSFETs are used in pairs.

RCA Semiconductor developed with the 4000 series, the first logic family in CMOS technology, which then - like the 7400 family in the TTL technology - prevailed as an industry standard and was produced by various manufacturers. Compared with TTL, this family is characterized by very low power consumption, a wide range for the supply voltage, but also slow switching operations and underperforming output driver.

A major weakness of 4000 was the high sensitivity to electrostatic discharge (ESD, Eng. Electrostatic discharge ), which could easily lead to the destruction of the circuit. The logic family 4000B reduced this problem with improved input protection circuits and brought further improvements in the electrical specifications. The 4000 and later, the 4000B never reached the dissemination of TTL circuits, the 4000B but are still produced and used.

The 4000 family uses its own numbering, a quadruple NAND gate with two inputs, for example, 4011 ( '11 ) called and not 7400 ( or '00 74H00, 74L00, 74LS00, etc) as in the TTL devices. In addition to the differing number and the pin assignment is different: Although the IC of both families in the same 14-pin DIP are available, are inputs and outputs to other ports; The devices are not interchangeable in most cases. The exceptions with identical pin assignments ( for example, six inverter 4069 or 74C14 ) also partially both type names are printed.

The 74C logic family from National Semiconductor addresses this drawback: These blocks were indeed designed in CMOS technology, similar to the 4000B, but used numbering, function definitions and pin assignments of the 7400 series. The 74C family gained no great importance, but the subsequent CMOS 74HC families and 74AC.

74HC ... ( high-speed CMOS) and 74HCT ( high-speed CMOS with TTL - compatible inputs ) used numbering of the 74 logic blocks. Thus, they are pin compatible, functionally compatible and largely electrically compatible with the previous TTL circuits and also have comparable speeds. The advantage over those is the lower input current and the lower supply current requirement. 74HC ... and 74HCT ... differ in the allowable tolerance of the operating voltage and the allowed range of prohibited or input level. So, however, are the building blocks of the series 74HCT ... with their inputs compatible to 5 V TTL logic levels ( and 3.3 volt logic levels ), 74HC ... not. Since the 1980s, there is the Series 74AC (Advanced -high-speed ) and 74ACT (Advanced -high-speed TTL - compatible inputs ).

Other logic families

Other logic families are:

  • Slow fail-safe logic ( LSL) - also known as high-level logic (HLL ) known
  • Emitter coupled logic ( ECL)
  • Integrated injection logic (I ² L or IIL ) - also known as current injection logic Merged Transistor Logic (MTL ) and the current - Hogging Injection Logic ( CHIL ) known
  • Gunning Transceiver Logic ( GTL) - used inter alia to the bus signaling in Intel CPUs P6, NetBurst and Core families; otherwise not widespread
  • Important building blocks highlighted in red
  • Standard CMOS devices operate with either 5 V or 15 V; the corresponding values ​​are right next to it