D. Column-Level SSADC
Fig. 8 shows the schematic of two neighboring column-level
SS-ADCs. A double stage comparator is used to reduce the
offset [17]. Fig. 9 shows the timing diagram of the whole
readout chain. After the reset of the SN, the auto-zeros of
the consecutive column-level amplifier and comparators are
opened sequentially in order to minimize the impact of charge
injection [9]. Then the charges are transferred to the SN and
the voltage at the input of the comparator is equal to the
difference between the transfer and reset levels. The ramp is
then activated together with the counter. Shift registers are
used in order to memorise the 10 bit code once the output
of the comparators is high. The CDS time is defined by the
time between the opening of the AZs and the moment when