Jitter comparison of tones generated by squaring and by fourth-power circuits

The tone-to-jitter power ratio is calculated for some conventional methods of generating a tone at the pulse repetition frequency of a PAM data signal by operating on the latter by an appropriate nonlinearity. Attention is focused on this ratio for a fourth-order nonlinearity, which will produce a tone even in the absence of excess bandwidth, and on this ratio for a square-law nonlinearity for small excess bandwidth. If the excess bandwidth is less than about 50 percent, the fourth power is superior. In particular, it yields a 10-dB improvement for 12 percent roll-off and binary data.