Analog delay based fractionally spaced n-tap feed-forward equalizer for wireline and optical transmitters

Abstract

An analog-based architecture is used to produce tap spacings in an n-tap fractionally-spaced equalizer without the need for digital clock-driven elements. The analog voltage-controlled delay cell circuits control the amount of applied delay based on the measured phase difference between quarter-rate clock signals. Because low speed clock signals are sufficient for comparison purposes, the analog delay cells can be placed before the quarter-rate multiplexors in the data path. The use of analog-based delay cells eliminates the need to route high-speed clock signals to multiple digital delay elements that are typically used to achieve fractionally spaced data signals in n-tap FIR equalizers. Timing margin issues can also be eliminated since digital clocked elements are not used to produce the fractionally spaced delays. The analog-based delay approach also consumes less power relative equalizers that use multiple digital delay elements requiring high speed clock signals.