1. Kroupa, V.F.: Frequency synthesis: Theory, design and applications, (Griffin, London 1973), p. 234
2. Gardner, F.M.: Phase-lock techniques, 2nd edn(J. Wiley, New York 1979), p. 147
3. Kroupa, V.F.: Frequency synthesis: Theory, design and applications, (Griffin, London 1973),Chap.7,