A circuit whose output is proportional to the difference between the input signals is considered to be which type of amplifier?
Differential
Understanding Differential Amplifier Operation
An amplifier is an electronic circuit that increases the power or amplitude of an input signal. Different types of amplifiers exist, each designed for specific purposes based on how they process the input signal(s).
The question asks about a specific type of amplifier: one whose output is directly proportional to the difference between its input signals. This means the amplifier takes two input voltages, say $V_{in1}$ and $V_{in2}$, and produces an output voltage $V_{out}$ such that $V_{out} \propto (V_{in1} - V_{in2})$.
Analyzing the Options
Let's examine the characteristics of each option to determine which one fits the description:
| Amplifier Type | Key Characteristic |
|---|---|
| Differential Amplifier | Produces an output proportional to the difference between two input signals ($V_{out} \propto V_{in1} - V_{in2}$). Designed to amplify difference signals and reject common-mode signals. |
| Darlington Pair | A two-transistor configuration that acts as a single transistor with very high current gain. It is not defined by its operation on the *difference* between two signals in the way the question describes. |
| Operational Amplifier (Op-Amp) | A high-gain, DC-coupled differential amplifier. While an op-amp is a *type* of differential amplifier and operates based on the difference between its inputs, the fundamental circuit described by the output being proportional to the difference is a differential amplifier itself. An op-amp is a more complex circuit built around a differential amplifier stage. |
| Common-mode Amplifier | This term usually refers to amplifying signals applied *identically* to both inputs (common-mode signals). Differential amplifiers are designed to *reject* common-mode signals, not amplify them. Common-mode operation describes a mode of input signal, not an amplifier type designed specifically to amplify the common-mode difference. |
Conclusion
Based on the definitions, the amplifier whose output is proportional to the difference between the input signals is the Differential amplifier. An operational amplifier uses a differential amplifier as its core stage but is a more complex integrated circuit.
Revision Table: Amplifier Types
| Amplifier Type | Primary Function | Input(s) | Output Relation (Simplified) |
|---|---|---|---|
| Differential Amplifier | Amplify difference between two inputs | Two (non-inverting, inverting) | $V_{out} \propto (V_{in1} - V_{in2})$ |
| Single-ended Amplifier | Amplify a single input signal | One | $V_{out} \propto V_{in}$ |
| Operational Amplifier (Op-Amp) | Versatile amplifier circuit (uses differential stage) | Two (non-inverting, inverting) | $V_{out} \approx A_{OL} (V_{in+} - V_{in-})$ (Open Loop Gain is very high) |
| Darlington Pair | Increase current gain | Input base/gate | High current gain configuration |
Additional Information on Differential Amplifiers
Differential amplifiers are fundamental building blocks in many electronic circuits, especially in operational amplifiers. Their key advantage is the ability to reject common-mode signals, which are unwanted noise or interference signals present equally on both inputs.
Key characteristics of a differential amplifier:
- It has two inputs: a non-inverting input and an inverting input.
- It amplifies the voltage difference between these two inputs.
- It ideally rejects common-mode signals (signals common to both inputs).
- The ability to reject common-mode signals is measured by the Common-Mode Rejection Ratio (CMRR). A high CMRR indicates better common-mode rejection.
- Differential amplifiers are less susceptible to noise picked up on the signal lines compared to single-ended amplifiers, especially in noisy environments or over long distances.
They are widely used in instrumentation, audio systems, and other applications where processing the difference between two signals is crucial or where noise rejection is important.
Important Questions from Op-Amp and Its Applications
Identify the circuit which is not the application of op-amp.
What is the ideal input resistance of an Op-amp (operational amplifier)?
Which of the following Op-Amp (operational amplifier) circuit configurations primarily operates in a non-linear mode?
Which type of multivibrator is commonly used for pulse stretching or generating a single output pulse of a predetermined duration upon receiving an input trigger?
In an ideal op-amp, the common mode gain is _____________.
