Describe the operation of a differential amplifier.
1 Answer
A differential amplifier is an electronic circuit that amplifies the difference between two input signals while rejecting any common-mode signals. It is a fundamental building block in various electronic circuits, especially in applications where noise rejection and signal amplification are crucial, such as in audio amplifiers, instrumentation amplifiers, and communication systems.
The basic operation of a differential amplifier involves two inputs, usually labeled as "+IN" and "-IN", and two outputs, often referred to as "OUT" and "OUT_B" (output with inverted polarity). The amplifier amplifies the voltage difference between the two input terminals (the differential voltage) and ideally ignores any voltage that is common to both inputs.
Here's a step-by-step description of how a differential amplifier operates:
Input Stage: The differential amplifier consists of two transistors (usually bipolar or field-effect transistors) with their emitters (or sources in the case of FETs) tied together and acting as a differential input pair. The bases (or gates) of these transistors receive the two input voltages, +IN and -IN.
Differential Mode: When the two input voltages, +IN and -IN, are different, a voltage difference or "differential voltage" (V_diff) is created between the bases of the transistors. This differential voltage causes an imbalance in the collector (or drain) currents of the transistors.
Amplification: The transistor with the higher collector current becomes more conductive, while the other transistor reduces its conductivity. This action results in the amplification of the differential voltage at the outputs.
Common-Mode Rejection: Any voltage that appears at both input terminals with the same polarity (common-mode voltage) is effectively canceled out by the differential amplifier. This property is crucial for noise rejection, as any noise or interference present in both input signals will be ignored, leaving only the desired differential signal amplified at the outputs.
Output Stage: The amplified differential voltage is then present at the outputs, OUT and OUT_B. These outputs can be used to drive subsequent circuitry or load.
The overall voltage gain (A_v) of the differential amplifier is determined by the transistors' characteristics and the circuit configuration. The gain can be controlled by adding external resistors or tail currents to bias the differential pair.
Differential amplifiers are widely used in operational amplifiers (op-amps) and other electronic systems, as they offer excellent performance in terms of signal amplification and noise rejection. Their ability to extract the difference between two input signals while rejecting common noise makes them essential components in many electronic devices and communication systems.
The basic operation of a differential amplifier involves two inputs, usually labeled as "+IN" and "-IN", and two outputs, often referred to as "OUT" and "OUT_B" (output with inverted polarity). The amplifier amplifies the voltage difference between the two input terminals (the differential voltage) and ideally ignores any voltage that is common to both inputs.
Here's a step-by-step description of how a differential amplifier operates:
Input Stage: The differential amplifier consists of two transistors (usually bipolar or field-effect transistors) with their emitters (or sources in the case of FETs) tied together and acting as a differential input pair. The bases (or gates) of these transistors receive the two input voltages, +IN and -IN.
Differential Mode: When the two input voltages, +IN and -IN, are different, a voltage difference or "differential voltage" (V_diff) is created between the bases of the transistors. This differential voltage causes an imbalance in the collector (or drain) currents of the transistors.
Amplification: The transistor with the higher collector current becomes more conductive, while the other transistor reduces its conductivity. This action results in the amplification of the differential voltage at the outputs.
Common-Mode Rejection: Any voltage that appears at both input terminals with the same polarity (common-mode voltage) is effectively canceled out by the differential amplifier. This property is crucial for noise rejection, as any noise or interference present in both input signals will be ignored, leaving only the desired differential signal amplified at the outputs.
Output Stage: The amplified differential voltage is then present at the outputs, OUT and OUT_B. These outputs can be used to drive subsequent circuitry or load.
The overall voltage gain (A_v) of the differential amplifier is determined by the transistors' characteristics and the circuit configuration. The gain can be controlled by adding external resistors or tail currents to bias the differential pair.
Differential amplifiers are widely used in operational amplifiers (op-amps) and other electronic systems, as they offer excellent performance in terms of signal amplification and noise rejection. Their ability to extract the difference between two input signals while rejecting common noise makes them essential components in many electronic devices and communication systems.