A sub-5 ps jitter time-to-digital converter ASIC with back-gate delay tuning in 22 nm CMOS

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 1080; p. 170784
• Main Authors: Quinn, Adam, Xie, Si, Apreysan, Artur, Fahim, Farah, Los, Sergey, Peña, Cristián, Lara, Carlos Eugenio Perez, Zimmerman, Tom, Braga, Davide
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2025
• Subjects: Cryo-CMOS; LGAD; Particle tracking detectors (solid-state detectors); SNSPD; Solid state detectors; TDC; Time-to-digital converter; Timing detectors; Timing detectors; TDC; Cryo-CMOS; Particle tracking detectors (solid-state detectors); SNSPD; LGAD; Solid state detectors; Time-to-digital converter
• ISSN: 0168-9002
• DOI: 10.1016/j.nima.2025.170784

We present the design of a Time-to-Digital Converter (TDC) ASIC together with performance characterization results at cryogenic temperature (6-8 K), and at room temperature using emulated Low-Gain Avalanche Detector (LGAD) signals. The TDC design uses a two-step architecture with a ring-oscillator based counter and a Vernier delay line fine TDC. The TDC is implemented in an FD-SOI process, and back-gate tuning is used not only to correct threshold variation due to cryogenic operation, but also as a novel way to tune TDC delay elements with very little overhead. Using this technique, we demonstrate a design with very low power (0.5mW) and area (0.003mm2). We present test results using the Fermilab Constant Fraction Discriminator (FCFD) ASIC to produce discriminated signals from an internal charge injection mechanism that mimics the waveform and signal amplitude of minimum ionizing particles impinging on LGAD sensors. We characterize the time precision of the full system and verify that the TDC ASIC contributes a negligible amount to the total system time precision, fully consistent with the expected jitter contribution of less than 5 ps. The results presented here demonstrate the utility of our TDC for applications in physics and quantum communications.