What limitation do conventional op-amps have compared with rail-to-rail types?

What limitation do conventional op-amps have compared with rail-to-rail types?

• A. They cannot operate on any supply.
• B. They cannot swing input or output voltages to the supply rails.
• C. They have zero input bias current.
• D. They cannot be used with feedback.

Answer: (B)

Conventional op-amps have limited input common-mode ranges and output swing; the internal transistor stages need headroom away from the supply rails, so the input voltages and the output cannot reach the rails themselves. Rail-to-rail types are designed to extend that range, allowing inputs and outputs to swing very close to both supply rails. So the key limitation being tested is that these older op-amps cannot swing input or output voltages to the supply rails. The other statements aren’t correct: op-amps require a power supply, they do work with feedback, and they do have finite input bias currents.

Conventional op-amps have limited input common-mode ranges and output swing; the internal transistor stages need headroom away from the supply rails, so the input voltages and the output cannot reach the rails themselves. Rail-to-rail types are designed to extend that range, allowing inputs and outputs to swing very close to both supply rails. So the key limitation being tested is that these older op-amps cannot swing input or output voltages to the supply rails. The other statements aren’t correct: op-amps require a power supply, they do work with feedback, and they do have finite input bias currents.