Adaptive Cancellation of Inter-Symbol Interference in High-Speed Continuous-Time DACs

Inter-symbol interference (ISI) often limits the performance of high-speed continuous-time digital-to-analog converters (DACs) such as Nyquist-rate current-steering DACs. The most effective previously-published means of mitigating ISI is return-to-zero (RZ) pulse shaping. Unfortunately, such RZ DACs are significantly more sensitive to clock jitter than their non-return-to-zero (NRZ) counterparts, particularly at high clock rates, and they typically consume more than twice the power of comparable NRZ DACs. This paper proposes, demonstrates via simulation, and rigorously analyzes a calibration technique which circumvents the need for RZ pulse shaping by adaptively measuring and cancelling ISI over the DAC’s first Nyquist band. It can be operated in both foreground and background calibration modes, and is compatible and can share circuitry with a recently-published calibration technique that similarly cancels error from component mismatches and clock skew.