A 4-channel 10.3Gb/s backplane transceiver macro with 35dB equalizer and sign-based zero-forcing adaptive control

Maximum baud rate of electrical signaling over backplanes is limited by reflection and crosstalk noise at connectors as well as ISI caused by frequency-dependent dielectric loss. A DFE is an effective circuit to alleviate ISI without amplifying noise. A multi-tap DFE is often used in order to cancel long-tail ISI [1–3]. However, multiple DFE taps may limit maximum operation speed due to analog feedback when using non-speculative taps [1,2], or increase power and area exponentially when using multiple speculative taps [3]. Another approach is a combination of a 1-tap speculative DFE to get faster speed and a linear equalizer (LE) to cancel the long-tail ISI [4,5]. Adaptive control is challenging when combining LE and DFE, because the relationship between LE and DFE must be taken into account [5], and the sign-sign-least-mean-square (SS-LMS) algorithm [7] that is commonly used in DFEs is not applicable to some types of LE, or at the cost of increased power and area for parallel signal paths in LE [6]. The zero-forcing (ZF) algorithm for analog filters [8] is applicable to any type of LE, but it needs an ADC and a large amount of logic to perform matrix multiplication. A heuristic algorithm [5] requires an eye measurement circuit, microcontroller, and control software.