Candidate: Refik Yalcin
Date: April 22, 2026
Time: 10:00 AM
Location: Hybrid (EIT 3142 and Microsoft Teams)
Supervisor: Prof. Peter Levine
Co-Supervisor: Dr. Ahmet Camlica
All are welcome!
Abstract:
Spectral X-ray imaging using Single Photon Counting (SPC) detectors offers significant advantages for medical diagnostics, such as lower radiation doses and improved tissue contrast in mammography and computed tomography (CT). However, a major challenge in Readout Integrated Circuit (ROIC) design remains: how to fit complex spectral electronics into a tiny pixel footprint without sacrificing spatial resolution.
This seminar presents the modeling, design, and experimental measurement of a novel CMOS spectrographic SPC X-ray imager, designed for direct-conversion sensors like amorphous selenium and Cadmium Telluride. To achieve a highly compact 50 x 50 micron pixel pitch, this work moves away from traditional per-pixel digitization. Instead, we introduce a Frequency Division Multiplexing (FDM) architecture. By shifting the quantization circuitry entirely outside the active pixel array, a single shared 8-bit pipeline analog-to-digital converter (ADC) running at 200 MHz can serve an entire bank of pixels, effectively overcoming traditional area and count-rate limitations.
The presentation will walk through the analog signal chain featuring an in-pixel charge-sensitive amplifier, a CR-RC shaper, and a local oscillator mixer, and detail how shaped pulses are modulated onto orthogonal carrier frequencies and summed via a transimpedance amplifier. Finally, we will share experimental results from the fabricated chip. The measurements demonstrate the successful end-to-end operation of the multi-carrier FDM scheme, achieving a 7.28-bit Effective Number of Bits (ENOB) and an average Equivalent Noise Charge (ENC) of 96 electrons. While discussing the trade-offs of the current-summing architecture, this talk will show how FDM provides a viable, scalable path for the next generation of high-resolution SPC imagers.