We present modeling and analysis of carrier dynamics in a single-photon avalanche diode (SPAD) operated with a capacitive quenching (CQ) method. The CQ method is regarded as a conventional resistive quenching (RQ) with its quenching resistance infinite or an open circuit. The SPAD is modelled as a lumped circuit consisting of a voltage dependent charge generator representing an avalanching depletion region and a capacitance of the depletion region and parasitic components. The carrier dynamics inside the device is described by time-dependent bipolar continuity equations (BCE) derived from the carrier continuity equations. We solve the BCE numerically with a 0.1 ps time resolution and investigate numbers of carriers in each circuit element as functions of time and of excess bias voltage (|𝑉ex|). We find two important characteristics of the CQ method; (1) a single-photon triggered Geiger-mode pulse is guaranteed to be quenched in a stable state (2) a voltage drop of the internal bias of SPAD due to the charges stored on the capacitance is proportional to |𝑉ex| with the proportionality factor of two. The results, in turn, enables one to design a SPAD free from after-pulse and from overflow. Such a SPAD pixel is shown to be compatible with a conventional complementary metal-oxide semiconductor (CMOS) image sensor (CIS) with a four transistors configuration pixel circuit. Finally, effectiveness of the present methodology is demonstrated by the subrange synthesis (SRS) time-of-flight (ToF) ranging experiments using a 6 μm size 400 × 400 pixels SPAD-based CIS.
We present a day and night MOS imager based on a single plate on-chip interference color filter. The filter comprises
periodic multiple layers of TiO2 and SiO2, with an intermediate color selection layer (SiO2) to disturb the period of the
layers, analogous to a "defect" layer in the one-dimensional photonic crystal. A particular advantage of this filter is
flexibility of designing a spectral profile of each color. Thus, one unit cell of the present MOS imager is designed to have
three multi-spectral, i.e. R+IR, G+IR, B+IR, pixels and one IR dedicated pixel, which would never be realized by
ordinary pigment materials. Daytime color image signals are obtained by subtracting the IR pixel signal, as a reference,
from each signal of R+IR, G+IR and B+IR pixels. Nighttime black and white imaging is simply realized by using the IR
components of all the pixels as brightness signals. This enables seamless switching between the day and night operations
of a camera. Although the subtraction operation usually reduces the dynamic range (DR) and signal-to-ratio (SNR), in
particular at low color temperatures, we overcome the issues by employing a new design scheme of the color filter
comprising double defect layers for each visible pass band and narrow IR pass bands for common IR components. As a
result, signal degradations in SNR and DR are suppressed even at low color temperatures enabling daytime imaging in a
wide range of color temperatures from 2300 K to 6500 K.
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