Minhad, K. N., M. B. I. Reaz, and J. Jalil. “A Low Power 0.18-μm CMOS Phase Frequency Detector for High Speed PLL”. Elektronika Ir Elektrotechnika, vol. 20, no. 9, Nov. 2014, pp. 29-34, doi:10.5755/j01.eee.20.9.5312.