🔍 Key Concepts
• Transistor switching states (cutoff, active, saturation) and what happens when the base is driven high or low
• How a pair of transistors can be arranged to form a logic gate (e.g., AND, OR, NAND, NOR) using high/low inputs
• The relationship between input conditions (A and B) and which transistor(s) provide a path from collector to emitter
💭 Think About
• Ask yourself: when A and B are both high, which transistor bases receive enough drive current to turn fully on, and which remain off?
• Consider the case when either A or B is low: does that interrupt the current path for one transistor or both, and what does that do to Q1 and Q2?
• Think about what combination of A and B makes Q2 conduct: does Q2 need both transistors in series to be on, or just one of them?
✅ Before You Answer
• Verify for each option what the state of Q1 (saturated/on vs off) would be for (A,B) = (high,high), (high,low), (low,high), (low,low).
• Check whether Q2 can be on if Q1 is saturated: does Q1 being saturated help or prevent Q2 from getting current?
• Confirm whether the wording "either A or B low" matches an AND-type condition (both must be high) or an OR-type condition (any one high is enough) for the conduction path to Q2.