A voltage follower, also known as a buffer circuit, is a simple electronic circuit used to replicate an input voltage at its output while providing high input impedance and low output impedance. It is typically implemented using an operational amplifier (op-amp) in its unity-gain configuration.
The basic setup of a voltage follower circuit consists of an op-amp with its non-inverting input connected to the input voltage (Vin), its inverting input connected to the output voltage (Vout), and a feedback loop connecting the output back to the inverting input. The circuit is designed such that the op-amp tries to keep both inputs at the same voltage level, effectively making the output voltage equal to the input voltage:
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+---------+
Vin ----| |
| Op-Amp |---- Vout
| |
+---------+
Uses of a voltage follower (buffer) circuit:
Impedance Matching: One of the main applications of a voltage follower is impedance matching. When the load connected to the output has a low impedance and the source providing the input has a high impedance, a voltage follower can be used to prevent signal degradation due to impedance mismatch. It presents a high input impedance to the source and a low output impedance to the load, ensuring efficient signal transfer.
Isolation: In some cases, it may be necessary to isolate two parts of a circuit, preventing one from affecting the other. A voltage follower can provide this isolation because it has a high input impedance, so it does not load the source significantly, and it has a low output impedance, which means it can drive the load effectively.
Signal Buffering: In complex electronic circuits, signals may undergo attenuation or distortion as they pass through various stages. A voltage follower can act as a buffer, preventing these unwanted effects by isolating the preceding stage from the following stage, providing a clean and unaltered replica of the input signal at its output.
Voltage Level Shifting: A voltage follower can be used to shift the voltage level of a signal without affecting its shape or characteristics. By adjusting the reference voltage at the inverting input, the output voltage can be shifted up or down while maintaining the same signal shape.
Active Filter Design: Voltage followers are often used in the design of active filters to maintain a constant impedance level across the frequency spectrum.
Overall, a voltage follower (buffer) circuit is a fundamental building block in electronic systems, providing signal isolation, impedance matching, and signal preservation capabilities.