LUPA-1300_09 Datasheet, PDF (16/32 Pages) Cypress Semiconductor – 1.3MPxl High Speed CMOS Image Sensor

LUPA-1300
Timing
Timing of the pixel array
The timing of the image sensor can be divided in two major
parts. The first part of the timing is related with the timing of
the pixel array. This implies the control of the integration time,
the synchronous shutter operation, and the sampling of the
pixel information onto the memory element inside each pixel.
The signals needed for this control are described earlier and
Figure 12 shows the timing of the internal signals. Figure 13
should make the timing of the external signals clear.
Figure 13. Timing of the pixel array. All external signals are digital signals between 0 and 5V. The Reset_ds is only required
in case dual slope is desired
Table 10. Typical timings of the pixel array
Symbol
a
b
c
d
e
f
Name
Mem_HL
MEM_HL -Precharge
Precharge
Sample
Precharge-Sample
Integration time
Value
> 5 µsec
> 200 nsec
> 500 nsec
> 3.9 µsec
> 400 nsec
> 2 µsec
The timing of the pixel array is straightforward. Before the
frame is read, the information on the photodiode needs to be
stored onto the memory element inside the pixels. This is done
by means of the signals Vmemory, Precharge and Sample.
Precharge sets the memory element to a reference level and
Sample stores the photodiode information onto the memory
element. Vmemory pumps up this value to reduce the loss of
signal in the pixel and this signal must be the envelop of
Precharge and Sample. After Vmemory is high again, the
readout of the pixel array can start. The frame blanking time or
frame overhead time is thus the time that Vmemory is low,
which is about 5 sec. Once the readout starts, the photodiodes
can all be initialised by reset for the next integration time. The
duration of the reset pulse indicates the integration time for the
next frame. The longer this duration, the shorter the integration
time becomes. Maximum integration time is thus the time it
takes to readout the frame, minus the minimum pulse for reset,
which is preferred not to be less than 10 sec. The minimal
integration time is the minimal time between the falling edge
of reset and the rising edge of sample. Keeping the slow fall
times of the corresponding internal generated signals, a
minimal integration time is about 2 sec. An additional reset
pulse can be given during integration by Reset_ds to
implement the double slope integration mode.
Readout of the pixel array
Once the photodiode information is stored into the memory
element in each pixel, the total pixel array of 1280 * 1024
needs to be readout in less than 2 msec (2 msec - frame
overhead time = 1995 µsec). Additionally, it is possible that
only a part of the whole frame is read out. This is controlled by
the starting address that has to be downloaded and from the
end address, which is controlled by the synchronisation pulses
in x- and y direction. The readout itself is straightforward. Line
by line is selected by means of a sync-pulse and by means of
a Clock_y signal. Once a new line selected, it takes a while
(row blanking time) before the information of that line is stable.
After this row blanking time the data is multiplexed in blocks of
16 to the output amplifiers. A sync-pulse and a clock pulse in
the x-direction do this multiplexing.
Document Number: 38-05711 Rev. *C
Page 16 of 32
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