4. Basic filter blocks in cascade synthesis

Active filters using cascade synthesis are built using one or more second-order cells plus a first-order cell when the degree of the transfer function is odd. To create such cells, amplifiers, resistors and capacitors are combined in three types of looped combinations:

• single or multiple negative feedback loops ;

• positive feedback loops ;

• feedforward loops, to create transmission zeros.

Often, two or three of these types of loop are used simultaneously.

This paragraph presents the elementary blocks based on these principles.