- Logic Families Definition: Logic families are different approaches to designing digital integrated circuits, each with identical electrical characteristics.
- Electrical Characteristics: These include factors like supply voltage range, response speed, and power dissipation, crucial for circuit performance.
- Compatibility Importance: ICs from the same logic family ensure compatibility and proper function in digital systems.
- Types of Logic Families: Major types include bipolar families like TTL and MOS families like CMOS.
- TTL and CMOS Subfamilies: TTL and CMOS have various subfamilies with specific characteristics and applications.
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 and output levels, sink and source current, noise margin and fan-out.
Significance of Logic Families
A board built from one family can connect outputs to inputs inside that family without extra level shifting.
Mix different logic families and you usually need an interface for logic levels or drive current, or for a different supply. The family list is how you pick parts that actually drive each other. A mismatch shows up as a weak high, a slow edge or a damaged input.
Types of Logic Family
Digital ICs use bipolar transistors, MOS transistors or both. Bipolar families include diode logic (DL), emitter-coupled logic (ECL), resistor-transistor logic (RTL), diode-transistor logic (DTL) and transistor transistor logic (TTL). MOS families include PMOS, NMOS and CMOS. BiCMOS mixes bipolar and MOS devices on one chip.
DL, RTL and DTL are museum pieces. New digital glue is almost all CMOS. Vintage TTL and ECL still appear in catalogues. Classic NMOS logic families are historical. BiCMOS shows up in some older bus drivers. This page sketches those families.
TTL subfamilies follow.
Bipolar TTL itself split into speed and power grades: standard, low-power, high-power, Schottky, low-power Schottky, advanced Schottky, advanced low-power Schottky and Fast. Commercial 74 and military 54 prefixes mark those grades: 74/54 standard, 74L/54L low-power, 74H/54H high-power, 74LS/54LS low-power Schottky and so on.
CMOS subfamilies
CMOS is the volume family. It includes 4000A, 4000B, 4000UB plus 54/74C, 54/74HC, 54/74HCT, 54/74AC and 54/74ACT. Those lines differ in supply range, speed and whether inputs tolerate TTL levels (the T suffix). A 74HC part is CMOS, not bipolar TTL, even with a 74 number.
ECL Subfamilies
ECL is emitter-coupled logic. Motorola launched MECL in 1962. ON semiconductor later inherited that bipolar line. The first series was MECL I. MECL II, MECL III, MECL 10K and MECL 10H followed.
