Sallen-Key, Multiple Feedback, State Variable, and Biquad Filters

This page compares the Sallen-Key filter, multiple feedback filter, state variable filter, and Biquad filter. It discusses low-pass and high-pass equivalents of these second-order filter types, specifically covering:

• Sallen-Key low-pass filter
• Sallen-Key high-pass filter
• Multiple feedback low-pass filter
• Multiple feedback high-pass filter
• 2-pole state variable filter
• Standard 2-pole Biquad filter and its high-pass equivalent

All of these filters are based on operational amplifier (Op-Amp) configurations, using both inverting and non-inverting combinations.

Sallen-Key Low-Pass Filter

Figure 1: Sallen-Key Low-Pass Filter

Figure 1 shows a Sallen-Key low-pass filter using an Op-Amp and includes its transfer function.

Sallen-Key High-Pass Filter

Figure 2: Sallen-Key High-Pass Filter

Figure 2 illustrates a Sallen-Key high-pass filter with 2 poles, as well as the low-pass equivalent of the design.

Multiple Feedback Low-Pass Filter

Figure 3: Multiple Feedback Low-Pass Filter

Figure 3 depicts a multiple feedback filter configured as a low-pass filter.

Multiple Feedback High-Pass Filter

Figure 4: Multiple Feedback High-Pass Filter

Figure 4 shows a multiple feedback filter implemented as a high-pass filter.

State Variable Filter (2-Pole)

Figure 5: State Variable Filter (2-Pole)

Figure 5 illustrates a 2-pole state variable filter.

Biquad Filter (2-Pole)

Figure 6: Biquad Filter (2-Pole)

Figure 6 shows a standard 2-pole Biquad filter, including a high-pass filter configuration of the Biquad type.