A differential amplifier is an electronic circuit that amplifies the difference between two input signals while rejecting any common-mode signals that are present in both inputs. It is a key building block in many analog circuits, including operational amplifiers, instrumentation amplifiers, and analog-to-digital converters.
The basic structure of a differential amplifier consists of two input terminals, labeled as inverting and non-inverting, and an output terminal. The input signals are connected to the inverting and non-inverting inputs, and the amplifier amplifies the voltage difference between them.
Features of Differential amplifier
- Amplifies voltage difference between two input signals
- High input impedance
- Rejects common-mode signals
- Gain control
- Low noise
- High bandwidth
Types of Differential amplifier
There are several types of differential amplifiers but the main types are:
Voltage-Differential Amplifier (VDA)
This type of differential amplifier amplifies the voltage difference between two input signals to produce an output voltage. It is commonly used in operational amplifiers and instrumentation amplifiers.
Current-Differential Amplifier (CDA)
This type of differential amplifier amplifies the current difference between two input signals to produce an output current. It is commonly used in applications where high common-mode rejection is required, such as in data transmission systems.
Fully-Differential Amplifier (FDA)
This type of differential amplifier has two differential input signals and two differential output signals. It is commonly used in high-speed data acquisition and transmission systems.
Instrumentation Amplifier
This is a specialized type of differential amplifier that has high input impedance, high common-mode rejection, and variable gain. It is commonly used in applications where high precision is required, such as in medical equipment and measurement systems.
Working of Differential amplifier
The basic operation of a differential amplifier involves using a pair of transistors, which are arranged in a way that allows them to amplify the voltage difference between the two input signals.
The two input signals are applied to the base of the transistors, with one signal applied to the base of one transistor and the other signal applied to the base of the other transistor. The emitters of the transistors are both connected to a common node, and the output signal is taken from the collector of one of the transistors.
The voltage difference between the two input signals causes a corresponding difference in the base-emitter voltage of the two transistors, which in turn causes a difference in their collector currents. This difference in current generates an amplified output signal at the collector of the transistor from which the output is taken.
Any common-mode signal that is present in both input signals is rejected by the differential amplifier because it causes an equal change in the base-emitter voltage of both transistors, which results in no difference in their collector currents.
The gain of a differential amplifier can be controlled by adjusting the values of the resistors that are connected to the emitters of the transistors. By varying these resistor values, the amount of feedback to the differential amplifier can be adjusted, which in turn controls the gain of the amplifier.
Applications
- Instrumentation: used in measurement and testing equipment, such as voltmeters and oscilloscopes.
- Audio Amplification: used in high-fidelity audio equipment, such as preamplifiers and amplifiers.
- Communication: used in modulators, demodulators, and data transmission systems.
- Medical: used in medical equipment, such as ECG machines and EEG machines.
- Industrial control: used in control systems for manufacturing and automation.
- Signal processing: used in filters, analog-to-digital converters, and digital-to-analog converters.