Use of input current and quiescent supply current in logic gates

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SUMMARY

The discussion focuses on the definitions and applications of input current and quiescent supply current in logic gates. Input current varies by logic family; for example, bipolar TTL logic utilizes an NPN transistor's emitter, resulting in higher input current, while CMOS logic employs MOSFET gates, leading to significantly lower input current. Quiescent supply current refers to the current drawn by a gate when it is not actively switching, indicating the static state of the inputs.

PREREQUISITES
  • Understanding of logic gate operation and types
  • Familiarity with bipolar TTL and CMOS logic families
  • Knowledge of transistor operation, specifically NPN and MOSFET
  • Basic concepts of electrical current and power supply characteristics
NEXT STEPS
  • Research the differences between bipolar TTL and CMOS logic families
  • Study the operation of NPN transistors in logic circuits
  • Learn about MOSFET characteristics and their role in CMOS technology
  • Explore quiescent current measurements and their implications in circuit design
USEFUL FOR

Electronics engineers, circuit designers, and students studying digital logic who seek to understand the operational characteristics of logic gates and their power consumption profiles.

Deathfish
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What is the meaning and use of input current in logic gates?

Also meaning and use of quiescent supply current.
 
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Deathfish said:
What is the meaning and use of input current in logic gates?

Also meaning and use of quiescent supply current.

Depending on the logic family, the gate will have some amount of input current to hold the input high or low. Look at the equivalent circuit for the gate to see where the current comes from (or goes to). Bipolar TTL type logic typically is using an NPN transistor's emitter at the input to the gate. CMOS logic typically has the inputs going to the gates of MOSFETs, so the input current for CMOS logic is much less than for bipolar TTL.

Quiescent power supply current for a gate is just the current that it draws when there is no logic level switching going on (the inputs to the gate are static).
 

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