What is meant by the term “op-amp input offset voltage”?
The correct answer is C: The differential input voltage needed to bring the open loop output voltage to zero. Op-amp input offset voltage is the differential input voltage (difference between the two input terminals) that must be applied to bring the open-loop output voltage to zero when no signal is applied.
In an ideal op-amp, with both inputs at the same voltage, the output should be zero. However, real op-amps have small manufacturing variations that cause a small voltage difference between the inputs even when the output is zero. This required input voltage difference is the offset voltage. It's typically in the millivolt range. Offset voltage is an important specification because it causes errors in DC-coupled applications. Many op-amps have offset null adjustment pins to minimize this error.
Exam Tip
Offset voltage = Input voltage to zero output. Remember: Input offset voltage is the differential input voltage needed to make the open-loop output voltage zero. It's typically a few millivolts.
Memory Aid
"**O**ffset **V**oltage = **O**utput **Z**ero **I**nput (think 'OV = OZI' = Output Zero Input, voltage needed)"
Real-World Application
You're using an op-amp in a DC amplifier circuit. Even with both inputs connected to ground, the output might be a few millivolts instead of zero. This is due to input offset voltage - a small voltage difference between the inputs that's needed to make the output zero. You can use the op-amp's offset null adjustment to minimize this error.
FCC Part 97.3Key Concepts
Why Other Options Are Wrong
Option A: Incorrect. This describes output voltage minus input voltage, which isn't the definition of offset voltage. Offset is about the input voltage needed, not the difference between output and input.
Option B: Incorrect. This describes the relationship between op-amp output and the next stage's input, not the op-amp's own offset voltage.
Option D: Incorrect. This describes the potential between inputs in open loop, but offset voltage specifically refers to the voltage needed to make the output zero.
题目解析
The correct answer is C: The differential input voltage needed to bring the open loop output voltage to zero. Op-amp input offset voltage is the differential input voltage (difference between the two input terminals) that must be applied to bring the open-loop output voltage to zero when no signal is applied. In an ideal op-amp, with both inputs at the same voltage, the output should be zero. However, real op-amps have small manufacturing variations that cause a small voltage difference between the inputs even when the output is zero. This required input voltage difference is the offset voltage. It's typically in the millivolt range. Offset voltage is an important specification because it causes errors in DC-coupled applications. Many op-amps have offset null adjustment pins to minimize this error.
考试技巧
Offset voltage = Input voltage to zero output. Remember: Input offset voltage is the differential input voltage needed to make the open-loop output voltage zero. It's typically a few millivolts.
记忆口诀
**O**ffset **V**oltage = **O**utput **Z**ero **I**nput (think 'OV = OZI' = Output Zero Input, voltage needed)
实际应用示例
You're using an op-amp in a DC amplifier circuit. Even with both inputs connected to ground, the output might be a few millivolts instead of zero. This is due to input offset voltage - a small voltage difference between the inputs that's needed to make the output zero. You can use the op-amp's offset null adjustment to minimize this error.
错误选项分析
Option A: Incorrect. This describes output voltage minus input voltage, which isn't the definition of offset voltage. Offset is about the input voltage needed, not the difference between output and input. Option B: Incorrect. This describes the relationship between op-amp output and the next stage's input, not the op-amp's own offset voltage. Option D: Incorrect. This describes the potential between inputs in open loop, but offset voltage specifically refers to the voltage needed to make the output zero.
知识点
Input offset voltage, Op-amp offset, Differential input, Op-amp errors
Verified Content
Question from official FCC Extra Class question pool. Explanation reviewed by licensed amateur radio operators.