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Comparison of IC Logic Families

Chapter · April 2017

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 Comparison of Logic Families

Logic Family (Silicon Technology) Introduction Features Limitations

- In common use before the development - Low speed, high power dissipation
1. RTL - First logic family, require minimum number
of ICs. Common Emitter Configuration. - Low fan out, poor noise immunity
(Resistor Transistor Logic) of transistors.
- Logic 1: 1-3.6 V and Logic 0: 0.2V - Operating speed <4MHz.
2. DCTL - Direct coupled transistors. - Simpler than RTL, easy to fabricate. - Small logic swing, poor noise margin.
)

(Direct Coupled Transistor Logic) - Base resistors of RTL are removed. - Fewer components hence economical. - Current hogging
Saturated Logic Families
ON − Saturation Mode
(Bipolar Transistor Technology)

OFF − Cut Off Mode

- First circuit configuration designed into IC.

- Use diodes and transistors.
Transistor Logic Families

3. DTL - Very small in size and high reliability at - No low and constant output impedance
- Input is fed through diodes followed by
(Diode Transistor Logic) very low price. in both states.
transistor at the output side.
- Greater fan out and improved noise margins.
- Use all transistors totem pole output. - Fast switching time, larger fan out. - Large current spike when switching
4. TTL
- Function of diodes in DTL is performed - Reduced silicon chip area. from low to high.
(Transistor-Transistor Logic)
by multi-emitter transistor at input - Easy to interface with other logic families. - Less noise immunity (0.4V)
(

- Merged Transistor Logic (MTL). - High component density, less power

5. IIL - Both PNP and NPN transistors are used. dissipation.
- Poor noise immunity.
(Integrated Injection Logic) - Designed around multi-collector - Low metal interconnection.
inverting transistors. - Used in MSI and LSI designs.
- Non saturated logic/Current mode logic. - Require large silicon area, high power
Non-Saturated Logic - Fastest logic family
6.ECL - Compliment output/eliminates the need dissipation (high cost).
ON − Active Mode - Used in very high frequency applications.
( ) (Emitter Coupled Logic) of inverter. - Inconvenient voltage levels.
OFF − Cut Off Mode - No noise spikes, large fan out.
- Logic 1: -0.8 and Logic 0: -1.7 - Low noise margins.
7.MOS Logic - Use pMOS, nMOS or both with high
- Lower power dissipation. - Larger propagation due to high output
MOS Logic Families (Metal Oxide Semiconductor packaging density.
- Shorter rise and fall times. impedance.
(Unipolar Transistor Technology) Logic) - Easy to design and fabricate
- Large fan-out. - Noise margin is around 1V.
- Less power drawn due to gate dielectric.

Parameter RTL IIL DTL HTL TTL ECL MOS CMOS

Basic Gate NOR NOR NAND NAND NAND OR-NOR NAND NOR-NAND
Fan Out 5 Depends on Injector Current 8 10 10-20 25 20 20-50
Power Dissipation 12 mW 6 nW – 70 uW 8-12 mW 55 mW 10 mW 40-55 mW 0.2-10 mW 0.025-1.01 mW
Noise Immunity Nominal Poor Good Excellent Very Good Poor Good Very Good
Propagation Delay 12 nSec 25-30 nSec 30 nSec 4 nSec 10 nSec 1-2 nSec 300 nSec 70 nSec
Clock Rate 8 MHz - 72 MHz 4 MHz 35 MHz +60 MHz 2 MHz 10 MHz
Speed X Power 144 Less than 1 300 - 100 100 60 70

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