Eye opening monitor for optimized self-adaptation of low-power equalizers in multi-gigabit serial links

Abstract: In modern day communication systems, there is a constant demand for increase in transmission rates. This is however limited by the bandwidth limitation of the channel. Inter symbol interference (ISI) imposes a great threat to increasing data rates by degrading the signal quality. Equalizers are used at the receiver to compensate for the losses in the channel and thereby greatly mitigate ISI. Further, an adaptive equalizer is desired which can be used over a channel whose response is unknown or is time-varying. A low power equalizing solution in a moderately attenuated channel is an analog peaking filter which boosts the signal high frequency components. Such conventional continuous time linear equalizers (CTLE) provide a single degree of controllability over the high frequency boost. A more complex CTLE has been designed which has two degrees of freedom by controlling the high frequency boost as well as the range of frequencies over which the boost is applied. This extra degree of controllability over the equalizer response is desired to better adapt to the varying channel response and result in an equalized signal with a wider eye opening. A robust adaptation technique is necessary to tune the equalizer characteristics. Some of the commonly used techniques for adaptation of CTLEs are based on energy comparison criterion in the frequency domain. But the adaptation achieved using these techniques might not be optimal especially for an equalizer with two degrees of controllability. In such cases an eye opening monitor (EOM) could be used which evaluates the actual signal quality in time domain. The EOM gives an estimate on the signal quality by measuring the eye opening of the equalized signal in horizontal and vertical domain. In this thesis work a CTLE with two degrees of freedom with an EOM based adaptation system has been implemented.