Biomedical Engineering Reference
In-Depth Information
FIGURE 5-26
Sallen Key filter
topology. (a) Low
pass. (b) High pass.
FIGURE 5-27
Sallen Key
band-pass filter.
One is the Sallen Key filter topology, which is particularly valued for its simplicity.
The circuit produces a second-order (12 dB/octave) low-pass or high-pass response using
only two capacitors and two resistors and a unity gain buffer, as shown in Figure 5-26.
The band-pass configuration is slightly more complex, and it is shown in Figure 5-27
for a nonunity gain configuration.
Higher-order filters can be obtained by cascading these building blocks.
One of the more interesting topologies is that of the state-variable filter. As shown
in Figure 5-28, it consists of a number of cascaded integrators fed back into a summing
amplifier. This configuration emulates the state-space model of a linear time invariant
FIGURE 5-28
State-variable filter
topology.
