Sallen, R. P.; E. L. Key (March 1955). "A Practical Method of Designing RC Active Filters". IRE Transactions on Circuit Theory. 2 (1): 74–85. doi:10.1109/tct.1955.6500159. S2CID51640910.
Sallen, R. P.; E. L. Key (March 1955). "A Practical Method of Designing RC Active Filters". IRE Transactions on Circuit Theory. 2 (1): 74–85. doi:10.1109/tct.1955.6500159. S2CID51640910.