A Robust and Efficient Fault-Resilient RadHard ADPLL

The high pace emergence in semiconductor technologies and associated application demands have revitalized industries to explore power efficient, stable and fault tolerant digital communication solutions, particularly for time critical applications operating at higher frequency ranges. Thus strengthening low cost CMOS digital design with Radiation Hardened by Design (RHBD) approach can be of paramount significance compared against the high cost Radiation Hard by Process (RHBP) approach. With this motivation, in this paper a novel and robust All-Digital-Phase Locked Loop (ADPLL) design has been developed for frequency synthesis. Our ADPLL design model encompasses multiple novelties and contributions including Feedback-Divider-Less-Counter (FDLC) based ADPLL, predictive phase-frequency detection (PFD), enhanced Time to Digital Converter (TDC) to detect next-edge occurrence of the reference clock that reduces locking period and complexity. The predictive PFD applies a phase-prediction scheme that delays the clock-edges of the reference frequency with a calibrated amount that it always aligned towards the expected frequency clock edge. It makes TDC to be narrow enough to cover the reference and oscillator jitter. Our proposed ADPLL design applied a narrow range converter (TDC) that assist phase-error prediction, correction and phase detection. The reference clock delay facilitates accurate timing relationship estimation with the variable frequency and hence performs retuning of the variable clock to reduce locking period and reduce noise. The ADPLL design has exhibited satisfactory performance for the frequency synthesis with reference frequency of 20MHz and the synthesis frequency of 2.4 GHz meeting radiation hardened features. The simulation results has revealed that the proposed Rad Hard ADPLL design can be a potential solution for space communication systems by maintaining low jitter of 340ps and power consumption of 371.7mW, as the narrow range TDC designed can detect sample radiation induced impulse noise of 20ns, 1mV and correct it.