Sotner, R., N. Herencsar, J. Jerabek, R. Prokop, A. Kartci, T. Dostal, and K. Vrba. “Z-Copy Controlled-Gain Voltage Differencing Current Conveyor: Advanced Possibilities in Direct Electronic Control of First-Order Filter”. Elektronika Ir Elektrotechnika, vol. 20, no. 6, June 2014, pp. 77-83, doi:10.5755/j01.eee.20.6.7272.