Use of input current and quiescent supply current in logic gates

1. Aug 3, 2011

Deathfish

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

Also meaning and use of quiescent supply current.

2. Aug 4, 2011

Staff: Mentor

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).