A High Dynamic Range Hybrid CT/DT Delta-Sigma Modulator for Medical X-ray Imaging

This paper proposes a high dynamic range $4^{\text {th }}$-order $\Delta-\Sigma$ modulator (DSM) designed for column-parallel readout analog-to-digital converters (ADCs) in medical X-ray detectors. The design achieves improved power and area efficiency and better robustness against clock jitter and process mismatch by using a hybrid continuous-time (CT) and discrete-time (DT) loop filter structure. The adoption of non-delayed DT integrators stabilizes the system and expands the maximum stable amplitude (MSA) to up to 0.7 Vpp under a 1.8 V power supply. The bandwidth of the proposed DSM is 24 kHz. With the presence of process mismatch, the implemented DSM can still achieve a dynamic range (DR) of about 96 dB with a 6.144 MHz sampling rate. The power consumption of the DSM is estimated as around $486.5 ~ \mu W$ by using a standard $180-\mathrm{nm}$ CMOS process.