Pufferstufen

Pufferstufen are buffer stages used in analog electronics to decouple signal sources from following stages and to improve drive capability. Their main function is to present a high input impedance to the preceding circuit and a low output impedance to the load, thereby reducing loading effects, preserving signal shape, and enabling proper impedance matching between stages.

A buffer stage typically provides a voltage gain close to one, so the signal amplitude is preserved while the stage can deliver more current to the next stage. Common implementations include a common-collector transistor stage (emitter follower), which offers very low output impedance and moderate current gain, and an operational amplifier configured as a unity-gain buffer (voltage follower). Other variants use field-effect transistors as source followers.

Key design considerations include ensuring adequate drive current for the intended load, maintaining sufficient bandwidth, and managing noise and offset. Transistor-based buffers introduce a small voltage drop (Vbe) and depend on transistor gain, while op-amp buffers rely on the amplifier’s supply rails, input bias currents, offset, and unity-gain bandwidth. Stability with capacitive loads is important; sometimes small resistors or compensation networks are used to prevent oscillations.

Applications span audio equipment, sensor interfaces, instrumentation, and readout circuits where a high-impedance source must drive a lower-impedance stage or long interconnects. Pufferstufen are not intended to amplify voltage; their value lies in impedance matching and signal integrity, enabling subsequent stages to operate without distortion or loss due to loading.