Which term describes the error voltage caused by input bias currents?

Which term describes the error voltage caused by input bias currents?

• A. Input bias current
• B. Common mode error
• C. Voltage gain
• D. Output offset voltage

Answer: (D)

The key idea is that real op-amps have input bias currents that flow into or out of the input terminals. When these currents pass through any source resistance, they create small voltage drops at the inputs. Because the amplifier has finite gain with feedback, that input-side error is amplified and shows up as a DC offset at the output. That observable offset at the output, caused by those bias currents, is what we call the output offset voltage. So, while the bias currents themselves are the currents entering the inputs, the specific error you measure at the output due to their effect is the output offset voltage. The other terms don’t describe this observable error: the input bias current is the current itself, common-mode error relates to common-mode effects rather than bias-induced output offset, and voltage gain is simply how much the input is amplified, not an error voltage.

The key idea is that real op-amps have input bias currents that flow into or out of the input terminals. When these currents pass through any source resistance, they create small voltage drops at the inputs. Because the amplifier has finite gain with feedback, that input-side error is amplified and shows up as a DC offset at the output. That observable offset at the output, caused by those bias currents, is what we call the output offset voltage.

So, while the bias currents themselves are the currents entering the inputs, the specific error you measure at the output due to their effect is the output offset voltage. The other terms don’t describe this observable error: the input bias current is the current itself, common-mode error relates to common-mode effects rather than bias-induced output offset, and voltage gain is simply how much the input is amplified, not an error voltage.