Use the full performance of differential amplifiers

The differential amplifier is a fundamental component in electronics and electrical engineering. It plays a central role in several applications, including signal processing, amplification and noise reduction. In this article, we take a deep dive into the world of differential amplifiers and explore their principles, applications, benefits, and more.

What is a differential amplifier?

A Differential Amplifier often called a “differential amplifier”, is a basic electronic circuit that amplifies the difference between two input signals and suppresses common mode signals. Common mode signals appear equally at both inputs and are generally considered noise. Because differential amplifiers only amplify the difference between the two input signals, they are essential in applications where signal fidelity and noise rejection are critical.

Principles of Differential Amplification

Differential amplifiers subtract one input voltage from another and produce an output voltage that is proportional to the difference between the two. And this is how it works:

• Two inputs, one output: A differential amplifier has two inputs, usually called V₁ and V₂ , and a single output, Vout . It calculates the voltage difference between V₁ and V₂ and reinforces it.
• Common Mode Rejection: One of the main functions of a differential amplifier is its ability to reject common mode signals. Any signal that is equally present in both inputs is canceled in the subtraction process, leaving only the difference signal.
• Gain gain: Differential amplifiers typically have a gain known as Aₙ . This gain determines how much the difference signal is amplified to produce the output voltage.

Applications of Differential Amplifiers

Differential amplifiers find application in various electronic systems due to their unique properties. Some common applications are:

Instrument amplifier

Instrumentation amplifiers used in various measuring instruments rely heavily on differential amplifiers. They provide high-precision amplification of small differential signals while suppressing common-mode interference, ensuring accurate measurements in applications such as medical instruments and sensor interfaces.

operational amplifier

Differential amplifiers are a fundamental element in operational amplifier circuits. Operational amplifiers generally use differential amplification to perform voltage amplification, signal conditioning, and filtering tasks.

Audio amplification

In audio devices, differential amplifiers amplify audio signals while minimizing background noise. This is crucial for high-quality audio output from devices such as amplifiers and preamps.

Advantages of Differential Amplifiers

Differential amplifiers offer several advantages that make them indispensable in many electronic systems:

• High Common Mode Rejection: The ability to effectively reject common mode signals ensures that only the desired differential signals are amplified, reducing noise and interference.
• Improved signal fidelity: Differential amplifiers preserve the integrity of the original signal and improve signal fidelity by only amplifying the difference between two input signals.
• Balanced Inputs: They offer a balanced input configuration that is particularly useful in applications where signal quality is of utmost importance.
• Versatility: Differential amplifiers can be configured for different gain values ​​and are therefore adaptable to different signal levels and applications.

Differential Amplifier Settings

They can be implemented using different components and electronic configurations. Here are two common types:

Differential amplifier with bipolar junction transistor (BJT)

A BJT-based differential amplifier uses bipolar junction transistors for amplification. This configuration is often found in analog electronic circuits due to its simplicity and versatility.

Operational amplifier differential amplifier (op-amp)

Due to the inherent characteristics of operational amplifiers, differential amplifiers based on operational amplifiers are widely used. They offer high input impedance, low output impedance, and excellent common mode rejection.

Differential amplifier circuit

Basic configuration of a differential amplifier

Differential amplifiers can be implemented with different electronic components, but the basic concept remains the same. Here we look at a basic differential amplifier circuit using bipolar transistors (BJTs):

Required components:

• Two NPN BJTs: These transistors serve as amplifier elements in the circuit.
• Resistors: Necessary to bias and adjust the gain of the differential amplifier.
• Input sources: V₁ and V₂ represent the differential input signals.
• Power source: Provides the necessary voltage levels for the transistors.

Circuit Operation:

• Pair of transistors: The two NPN BJTs are connected in a differential configuration with their collectors connected to each other and connected to the positive supply voltage ( Vcc ).
• Bias: Proper polarization is critical to ensure BJTs operate within their active range. Bias resistors establish the necessary voltage levels at the transistor bases.
• Differential input: V₁ and V₂ are applied to the bases of the transistors. The pair of transistors amplifies the voltage difference between these inputs.
• Output voltage: The amplified difference signal appears at the collector node and can be considered as the output voltage Vout . The common mode component is effectively canceled so that only the desired difference signal is amplified.

Differential amplifier based on operational amplifier

Another common approach is to use operational amplifiers (op amps) to build a differential amplifier. Differential amplifiers based on operational amplifiers are known for their high input impedance, low output impedance, and ease of configuration. They offer excellent common mode rejection and are widely used in a variety of applications.

In this configuration, an operational amplifier amplifies the voltage difference between the two input signals, while feedback resistors adjust the gain.

Understanding how differential amplifiers work and circuit configurations is important for both engineers and electronics enthusiasts. These versatile circuits are used in a wide variety of areas and ensure signal accuracy and noise reduction in countless electronic systems.

Conclusion

In electronics, the differential amplifier is crucial in applications where precise signal amplification and noise rejection are essential. Understanding its principles, benefits and applications is crucial for anyone in electronics and electrical engineering. Whether you are developing precision measurement devices, audio equipment, or signal processing circuits, the differential amplifier is a valuable tool in your arsenal that ensures the fidelity and accuracy of your electronic systems.

Common questions

What is the main advantage of a differential amplifier over a single-ended amplifier?

The main advantage of a differential amplifier is its ability to effectively reject common mode signals. This ensures that noise or interference affecting both input lines is canceled out equally, resulting in cleaner, more accurate amplification of the differential signal.

How can I calculate the gain of a differential amplifier?

The gain of a differential amplifier can be calculated using the following formula: Gain (Aₙ) = (Rf/Re) * (1 + 2 * (Re/Re2)), where Rf is the feedback resistor, Re is the feedback resistor. emitter and Re2 is the second emitter resistor in a BJT-based configuration.

Can I use a differential amplifier in audio devices to improve sound quality?

Yes, differential amplifiers are often used in audio devices to improve sound quality. They help reduce background noise and interference, resulting in clearer audio output and making them a valuable component in amplifiers and preamps.