Radiation-Hardened Delta-Sigma CDC

This project implements a novel time-based capacitance-to-digital converter (CDC) fabricated in a commercial 65 nm CMOS technology. The radiation-hardened CDC is targeted for use with capacitive sensor interfaces in harsh radiation environments. It is expected to operate with minimal performance variation with respect to TID (up to 10 MGy-Si) and SEL tolerance up to 65 MeV.cm \(^2\) /mg. In particular, during HEP experiments, the relative humidity is measured to ensure the “dryness” of the Si-detectors before being cooled down below zero temperatures to avoid vapor condensation. Miniaturized integrated capacitive humidity sensors are installed along with the detector assembly to monitor the humidity readings and the dew point temperature. The CDC prototypes are fully designed using time-based digital-gate-like circuits. The CDC uses 1st order \(\Delta \Sigma \) quantization noise shaping to improve the measured capacitance resolution. The prototype supports capacitance measurement within the range of 0–3.75 pF. The CDC samples achieve an effective-number-of-bit (ENOB) of 12.9 bits with an energy efficiency of 0.18 pJ/-step. The CDC is implemented with various radiation hardened-by-design techniques to withstand TID-induced performance degradation and equipped with TMR to minimize SEE-induced fluctuations. The performance of the CDC prototype under heavy-ion exposure is also evaluated in this experiment. The results are analyzed to determine the susceptibility of SEE-induced fluctuations and validate the effectiveness of the various radiation-hardened design techniques used inside the chip. This chapter is arranged as follows: Section 5.1 discusses the prior art. Section 5.2 elaborates on the architecture and explains the proposed time-based \(\Delta \Sigma \) -CDC theory. Section 5.3 discusses the circuit-level implementation of the CDC in detail. The measurement setup for the CDC design is described in Sect. 5.4, and the results obtained are analyzed and discussed to assess the performance. Section 5.4 also describes in detail the experimental setup used for the heavy-ion experiment and presents the radiation test results. Section 5.5 concludes the chapter by summarizing the performance parameters of the implemented \(\Delta \Sigma \) -CDC prototype samples.