No abstract

A digital-to-time converter (DTC) produces a time delay based on a digital code. Similar to data converters, linearity is a key metric for a DTC and it can be characterized by its integral nonlinearity (INL). However, measuring the INL of a subpicosecond-resolution DTC is problematic, even when using the best available high-speed oscilloscopes. In this brief we propose a new method to measure the INL of a DTC by applying digital phase modulation and measuring the output spectrum with a spectrum analyzer. The frequency selectivity of this method allows for an improved measurement resolution down to a few femtoseconds and allows measuring an INL below 100 fs. The proposed method is verified by behavioral simulations and is employed to measure the INL of a high-resolution DTC realized in the 65-nm CMOS, with a time resolution of 25 fs and a standard deviation of 27 fs.

In this paper we propose and analyze a Pulse-Output Digital-to-Frequency Converter (DFC) generating square waves, that uses a Digital-to-Time Converter (DTC) to correct the spurious tones (spurs) in the output spectrum. We focus on high-level architectural potential, discuss the design features of a DTC suitable for the proposed system and we explore possibilities and limits of this approach in terms of cleanness of the output spectrum. Behavioral model simulations confirm the theoretical analysis presented. Besides an analytical description of the output spurs, we derive a closed-form estimate of the worstcase spur, that leads to a simple design equation. This is useful to determine the DTC requirements (number of bits, Integral Non-Linearity (INL)) given a certain Spurious-Free Dynamic Range (SFDR) target. We show that the maximum spur strength, in dBc, depends exclusively on the ratio between the output frequency and the clock frequency and the DTC features (number of bits, INL and other impairments) and increases with the ratio by 6 dB per octave.

PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Twente, op gezag van de rector magnificus, prof. dr. T.T.M. Palstra, volgens besluit van het College voor Promoties in het openbaar te verdedigen op vrijdag 8 juli 2020 om 16.45 uur door Claudia Palattella geboren op 19 juni 1983 te Putignano (BA), Italy