A Tracking Performance Comparison of the Conventional Data Transition Tracking Loop (DTTL) with the Linear Data Transition Tracking Loop (LDTTL)

The tracking (mean-square timing-error) performance of a linearized datatransition tracking loop (LDTTL) is presented. The difference between the LDTTL and the conventional DTTL is that the hard-limiter nonlinearity in the conventional DTTL’s inphase arm is replaced by a linear device, as suggested by the maximum a posteriori (MAP) open-loop estimate of symbol timing at low symbol signal-to-noise ratio (SNR). The application of such a configuration is for errorcorrection-coded communication systems where current coding technology suggests symbol SNR values perhaps as low as −6 dB. The mean-square tracking jitter performances of the LDTTL and the conventional DTTL are compared over a wide range of symbol SNRs, with the former offering a noticeable advantage at low symbol SNRs.