A Sallen-Key filter is an electronic filter topology used to design active filters, specifically low-pass, high-pass, band-pass, and band-reject filters. It was invented by R.P. Sallen and E.L. Key in 1955. This filter design is widely used due to its simplicity, ease of implementation, and relatively low component count.
Sallen-Key filters are implemented using operational amplifiers (op-amps) as active components. An op-amp is a type of amplifier that can amplify voltage signals and is commonly used in electronic circuits. The Sallen-Key filter uses the op-amp's high gain and negative feedback to achieve the desired filtering characteristics.
The two most common types of Sallen-Key filters are the low-pass and high-pass configurations. Let's briefly discuss these two versions:
Sallen-Key Low-Pass Filter:
The low-pass Sallen-Key filter attenuates high-frequency signals while allowing low-frequency signals to pass through with minimal loss. It consists of two resistors and two capacitors arranged in a specific configuration, typically as a second-order (two-pole) filter. This means it provides a steeper roll-off of the frequency response compared to a first-order filter.
Sallen-Key High-Pass Filter:
The high-pass Sallen-Key filter does the opposite of the low-pass filter. It attenuates low-frequency signals and allows high-frequency signals to pass through with minimal loss. Like the low-pass filter, it is also a second-order filter.
Both the low-pass and high-pass Sallen-Key filters can be designed to have specific cutoff frequencies and bandwidths by adjusting the values of the resistors and capacitors in the circuit.
Sallen-Key filters are widely used in various applications, including audio processing, signal conditioning, and communication systems, where accurate and stable frequency response is required. Their popularity is due to their relatively straightforward design, ease of implementation, and the ability to achieve good performance using a minimal number of components.