Logic Circuit Technologies|Logic Families Digital Electronics

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Logic Circuit Technologies/Families: Logic circuits can be built using different components like diodes, transistors, MOSFETs, Resistors etc. Based on the type of components used logic circuits are classified into different Logic Families. The following are the names of the circuit technologies used from the initial days of building logic circuits.

Logic Circuit Technologies/Families

  • DL- Diode Logic
  • RTL – Resistor Transistor Logic.
  • DTL – Diode Transistor Logic.
  • HTL – High Threshold Logic.
  • TTL – Transistor Transistor Logic.
  • IIL (I2L) – Integrated Injection Logic.
  • ECL – Emitter Coupled Logic.
  • MOS – Metal Oxide Semiconductor Logic (PMOS and NMOS).
  • CMOS – Complementary Metal Oxide Semiconductor Logic.

DL, RTL and DTL were the initial logic circuit design techniques. HTL is a variant of DTL which is used in environments where noise is very high. Now these are not in use.

At present only TTL and CMOS are most widely used devices. The following five basic types of logic families of devices are available in the form of ICs (chips) .

These are:

1. TTL: These devices use Bi-Polar transistors for their circuit design. Bi-Polar transistors are operated at cut off and saturation region only. TTL devices draw more amount of current compared to other logic families. These devices are available in 74, 74S, 74LS, 74AS, 74ALS, and 74F…. series. All digital functions are available in this logic family.

2. MOS Logic: It uses MOSFETs. It is again sub-classified as PMOS and NMOS logic families based on type of MOSFETs used. Memory chips and microprocessors are mostly from MOS logic family.

3. CMOS Logic: This logic uses complimentary pair of MOSFETs. CMOS devices come in 4000/4500 series, 74C series and also all other parts that are identified by the ‘C’ in the part number.

4. ECL: These devices also use bipolar transistors, but they operate in the linear region. ECL devices are available in 10K, 100K, or 10E series.

5. Bi-CMOS: Actually CMOS technology is used in analog, digital, and mixed-signal electronic circuit design. Now CMOS is further improved by combining bipolar transistors and MOSFETs in the circuits and it is called as Bi-CMOS technology.

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