What technique can be used to achieve impedance matching in audio or sensor interfaces?

• A. Use longer cables
• B. Increase load impedance
• C. Buffer stages or impedance matching networks
• D. Remove shielding

Answer: (C)

Impedance matching is about shaping what the source "sees" and what the load "sees" so the signal isn’t distorted or attenuated by mismatch. A buffer stage, such as a voltage follower or an op-amp configured as a buffer, isolates the source from the cable and the rest of the system. It presents a very high input impedance to the source (so the source isn’t loaded down) and a very low output impedance to the load and cable (so the signal can drive the following stages without losing amplitude or bandwidth). This keeps the amplitude stable, preserves frequency response, and prevents the load from varying the source’s behavior as different devices or cables are connected.

Impedance matching networks do the same job with passive components or transformers. They transform the source or load impedance to the values that the system expects, which can maximize power transfer or minimize reflections and frequency-dependent loss across the band of interest. In practice, many audio and sensor interfaces rely on a buffer to stop loading effects, and, when needed, a matching network or transformer to tailor the impedance precisely for the particular connection and frequency range.

Using longer cables tends to add capacitance and resistance that can worsen matching and high-frequency response, increasing load effects rather than solving them. Simply increasing the load impedance may help in some cases but doesn’t guarantee proper matching across the circuit or frequency range. Removing shielding would increase noise and EMI, not improve impedance matching.