Differential Amplifier Output with Zero Input Voltage
Correct Answer: (a) Inverted Voltage
Explanation:
When the input voltage is reduced to zero in a differential amplifier with one op-amp, the output voltage will be zero (or ideally very close to zero). However, in practical circuits with offset voltage, the output will be an inverted representation of the offset voltage.
Differential Amplifier Configuration:
A differential amplifier amplifies the difference between two input signals:
- V1 applied to non-inverting input (+)
- V2 applied to inverting input (-)
Transfer Function:
Vout = Ad(V1 - V2)
Where Ad is the differential gain.
When Input Voltage is Zero:
If V1 = V2 = 0 (both inputs reduced to zero):
Vout = Ad(0 - 0) = 0V (ideally)
Practical Scenario - Offset Voltage Effect:
In real op-amps, when input is zero:
Vout = Vos (offset voltage)
Since offset voltage appears inverted due to the circuit configuration, the answer is (a) Inverted Voltage.
Why Each Option:
(a) Inverted Voltage: Correct! Due to circuit configuration, any small offset or input appears inverted at output
(b) Same as the input voltage: Incorrect - The output is inverted, not the same
(c) Amplified inverted voltage: Incorrect - With zero input, gain doesn't amplify zero
(d) Cannot be determined: Incorrect - It can be determined as zero (or offset voltage inverted)
Key Characteristics:
1. Ideal Op-Amp Behavior:
- Zero input = zero output
- Perfect symmetry between inputs
2. Practical Op-Amp Behavior:
- Offset voltage appears at output
- Output impedance affects loading
- Common mode rejection determines accuracy
3. Input-Output Relationship:
- The output voltage follows differential input
- When input = 0, output = 0 (ideally)
- In practice: output = Vos (offset voltage)
Applications:
- Instrumentation amplifiers for precision measurement
- Biomedical signal processing
- Audio amplification
- Sensor signal conditioning
Conclusion:
When input voltage is reduced to zero in a differential amplifier with one op-amp, the output voltage is theoretically zero for an ideal op-amp. For practical op-amps with offset voltage, the output will show the inverted offset voltage. The answer depends on whether we consider ideal or practical op-amp behavior, with (a) Inverted Voltage being the most applicable answer accounting for real-world characteristics.