Surapong Siripongdee and  Witthaya Mekhum,  A Design of Electronically Tunable Voltagemode Universal Filter with High Input Impedance.   journal   = {International Journal of Electronics and Communication Engineering}, [online]. World Academy of Science, Engineering and Technology.
    January 2012, vol. 61(1). 40 - 43
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/273.