Tunable CMOS Delay Gate With Improved Matching Properties

This paper presents the analysis and design of a tunable CMOS delay gate with improved matching properties as compared with the commonly used “current starved inverter” (CSI). The main difference between these structures lies in the location of the current limiting transistor on the inverter´s output rather than on the side of the power rail. This improves the dynamic performance of the proposed “output split inverter” (OSI) circuit reducing the influence of the MOS transistor mismatch on the generated delay time variability. A test chip including two arrays consisting of 512 16-stage delay lines employing the CSI and OSI gates has been designed and fabricated in a standard 90 nm CMOS technology. The experimental results show that the proposed OSI circuit is about 10-50% more accurate than the conventional current starved inverter with no penalty in terms of the increased area, power consumption or complexity. Applications of the proposed circuit are in the design of time-to-digital converters (TDCs), delay locked loops, readout circuits for particle detection and time-based asynchronous computation systems.