A 113.3-dB Dynamic Range 600 Frames/s SPAD X-Ray Detector With Seamless Global Shutter and Time-Encoded Extrapolation Counter
IEEE Journal of Solid-State Circuits(2023)
摘要
This article presents a
$400 \times 200$
single-photon avalanche diode (SPAD) X-ray detector that supports seamless global shutter operation. The pixel consists of an SPAD with two time-encoded extrapolation counters. For use under low X-ray dose conditions, the pixels and readout circuitry operate in a fully digital manner, avoiding the noise penalty of the readout. Under high X-ray dose conditions, the proposed counter operates in the extrapolation mode and thus achieves a high dynamic range (HDR), while reducing the counter’s power consumption. This is achieved by capturing the time of the counter overflow (
$T_{\mathrm{ OF}}$
) and expanding the counter depth by the ratio between the integration time (
$T_{\mathrm{ INT}}$
) and
$T_{\mathrm{ OF}}$
. To reconstruct
$T_{\mathrm{ OF}}$
, a
$\phi _{\mathrm{ GCLK}}$
signal is distributed during
$T_{\mathrm{ INT}}$
and accumulated from
$T_{\mathrm{ OF}}$
to the end of
$T_{\mathrm{ INT}}$
by reusing the counter. This only requires distribution of the
$\phi _{\mathrm{ GCLK}}$
across the pixel array. Furthermore, seamless global shutter operation is realized through the use of two counters, which achieves a 100% temporal aperture for the X-ray photon. The proposed X-ray detector is implemented in a 1P5M 65-nm CMOS process. To be used for both medical diagnosis and industrial inspection, the pixel pitch is selected as 49.5
$\mu \text {m}$
. The
$400 \times 200$
detector achieves a dynamic range (DR) of 113.3 dB, while consuming only 127.2 mW. Compared with previous X-ray detectors, the proposed detector exhibits a 24.9-dB improvement in DR.
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关键词
seamless global shutter,frames/s,dynamic range,extrapolation counter,x-ray,time-encoded
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