74xx
A group of integrated circuits (ICs) in digital electronics is called 74xx chips . The numbers of all these circuits (chips) begin with the digits "74", hence the name. The simplest, first developed electronic chips of the series contain simple logical basic functions in the form of logic gates (AND, OR etc.), which were initially implemented as transistor-transistor logic . In the later development, circuit functions up to complex arithmetic units were integrated in these components .
history
The series was developed by Texas Instruments in the 1970s and is still being expanded. The oldest chips have existed practically unchanged since then. The sequence of digits with four to six digits is incremented continuously. The best-known representative is the 7400, a 4-way NAND gate with two inputs each.
In the meantime, various 74xx logic families have been developed that have been improved compared to the original, especially in terms of speed and power consumption. They are identified by additional letters (one or up to five letters) between "74" and "xx", for example 74LS00 (Low Power Schottky or Schottky-TTL ). The original series (without additional letters) has lost much of its importance today and is rarely used. The early home and personal computers of the 1970s and 1980s usually contained a large number of these chips. They were later largely replaced in computer technology by customer-specific, complex ICs ( ASICs ), each of which can replace a large number of 74xx ICs.
casing
Most of the 74xx chips exist as DIL housings and as SMD modules in SMD housing forms . They are offered by many semiconductor manufacturers with different prefixed code letters . Logic components are also available in a ceramic DIL housing.
Operating voltage
The original logic families were operated with a supply voltage of 5.0 V. As a further development of logic families in the direction of ever higher frequencies, the operating voltage was also reduced to 3.3 V or 2.5 V, for example. To connect logic families with different operating voltages (e.g. 3.3 V to 5.0 V), special logic families have been developed that have logic levels at the input and output that are compatible with other logic families.
Logic families
The original logic families were made in bipolar technology. In the course of time, logic families in CMOS technology and BiCMOS technology have been added. The logic families for very high clock frequencies are now almost exclusively implemented in CMOS or BiCMOS technology.
abbreviation | designation | description |
---|---|---|
Bipolar | ||
- | Standard TTL | - |
L. | Low power | Further development with lower power requirements; very slowly; obsolete and replaced by the LS series |
H | High speed | Further development with higher switching speed; obsolete and replaced by the S series; often used in computers in the 1970s |
S. | Schottky | outdated |
LS | Low power Schottky | |
AS | Advanced Schottky | |
AS | Advanced Low Power Schottky | |
F. | Nearly | Faster than the S series; comparable to the AS series |
CMOS | ||
C. | CMOS | Supply voltage from 5 to 15 V, similar to the 4000 logic family |
HC | High speed CMOS | Supply voltage from 2 to 6 V, similar speed to LS 12 ns, |
HCU | High speed CMOS unbuffered | Similar to HC, only without a buffer stage at the input and output |
HCT | High speed | Logic level compatible with TTL, only suitable for 5 volts |
AC | Advanced CMOS | |
ACT | Advanced CMOS | Logic level compatible with TTL |
AHC | Advanced high-speed CMOS | HC series with approx. 3 times the speed |
AHCT | Advanced high-speed CMOS | fast HC series with TTL-compatible logic levels |
ALVC | Low voltage | Low supply voltage of 1.65 to 3.6 V, running time 2 ns |
AUC | Low voltage | Low supply voltage of 0.8 to 2.7 V, running time less than 1.9 ns at 1.8 V. |
FC | Almost CMOS | Comparable to F |
LCX | Supply voltage 3.3 V; 5 V tolerant inputs | |
LVC | Low voltage | Supply voltage 1.65 to 5.5 V; 5 V tolerant inputs even with supply voltages <5 V. |
LVQ | Low voltage | Supply voltage 3.3 V. |
LVX | Low voltage | Supply voltage 3.3 V; 5 V tolerant inputs |
VHC | Very high speed CMOS | Similar to 'S' but in CMOS |
CBT | Very fast CMOS family for applications up to the GHz range; Supply voltage 5.0 V. | |
CBTLV | Low voltage | Very fast CMOS family for applications up to the GHz range, supply voltage 3.3 V. |
G | Super high speeds | For switching frequencies up to 1 GHz, supply voltage 1.65 to 3.3 V; 5 V tolerant inputs |
BiCMOS | ||
BCT | BiCMOS | Logic level compatible with TTL, primarily used for buffers. |
ABT | Advanced BiCMOS | TTL compatible logic level, faster than ACT and BCT |
ALB | Advanced BiCMOS | fast BiCMOS technology, supply voltage 3.3 V; used primarily for buffers |
ALVT | Advanced BiCMOS low voltage | fast BiCMOS technology, supply voltage 3.3 V; also 5 V tolerant; used primarily for buffers |
LVT | Advanced BiCMOS low voltage | fast BiCMOS technology, supply voltage 3.3 V; also 5 V tolerant; primarily for buffers |
Circuit development
In circuit development, logic families dominate today with low power consumption and a high maximum switching frequency. In practice, logic families with 3.3 V or 2.5 V are often used, since other components, for example PLDs , FPGAs , ASICs and modern microprocessors, are now also operated with the lower supply voltages . Furthermore, individual gate functions or individual flip-flops are practically no longer of any significance in the development of new assemblies. As far as possible, more complex logic components are used for this purpose which contain complete circuit functions in one component, or programmable logic components (PLD or FPGA components) are used. The logic components are usually used today in the SMD housing. Semiconductor manufacturers have often developed different component series for use in different continuous operating temperature ranges .
See also
literature
- The Engineering Staff: The TTL Data Book . tape 1 . Texas Instruments, 1989, ISBN 3-88078-078-1 .
- User Guide . Philips / NXP , 1997 ( nxp.com [PDF]).
- without author: digital design seminar . Texas Instruments, 2000.
Web links
- LOGIC Pocket Data Book (Rev. B - scyd 013b) PDF , 794 pages, data and connection diagrams from Texas Instruments.
- Electronics compendium