STAR1000
Document Number: 38-05714 Rev. *B
Page 8 of 21
Addressing Logic
The addressing logic allows direct addressing of rows and
columns. Instead of the one-hot shift registers that are often
used, address decoders are implemented. One can select a
line by presenting the required address to the address input of
the device and latching it to the Y- decoder logic. Presenting
the X- address to the device address input and latching it to
the X- address decoder can select a column.
A typical line read out sequence will first select a line by
applying the Y-address to the Y-decoder. Activation of the
LD_Y input on the Y-logic connects the pixel outputs of the
selected line to the column amplifiers. The individual column
amplifier outputs are connected to the output amplifier by
applying the respective X- addresses to the X- address
decoder. Applying the appropriate Y- address to the Y-
decoder and activating the “Reset” input reset a line. The
integration time of a row is the time between the last reset of
this row and the time when it is selected for read out.
The Y- decoder logic has two different reset inputs: RESET
and RESET_DS. Activation of RESET resets the pixel to the
Vdd level; activation of RESET_DS resets the pixel to the
voltage level on the VREF input. This feature allows the appli-
cation of the so called dual slope integration. If dual slope
integration is not needed, VREF is tied to Vdd and RESET_DS
must never be activated.
Column Amplifiers
All outputs from the pixels in a column are connected in parallel
to a column amplifier. This amplifier samples the output
voltage and the reset level of the pixel whose row is selected
at that moment and presents these voltage levels to the output
amplifier. As a result, the pixels are always reset immediately
after read out as part of the sample procedure. Note that the
maximum integration time of a pixel is the time between two
read cycles.
Output Amplifier and Analog Multiplexer
The output amplifier combines subtraction of pixel signal level
from reset level with a programmable gain amplifier. Since the
amplifier is AC coupled, it also contains a provision to maintain
and restore the proper DC level.
An analog signal multiplexing feeds the pixel signal to the final
unity gain buffer, providing the required drive capability. Apart
from the pixel signal, three other external analog signals can
be fed to the output buffer. All these signals can be digitalised
by the on-chip ADC if the output of this buffer is externally
connected to the input of the ADC.
The purpose of the additional analog inputs (A_IN1, A_IN2,
and A_IN3) is to allow the possibility of processing other
analog signals through the image sensors signal path. These
signals can then be converted by the ADC and processed by
the image controller FPGA. The additional analog inputs are
intended for low frequency or DC signals and have a reduced
bandwidth compared with the image signal path.
ADC
The image sensor has a 10-bit ADC that is electrically
separated from the rest of the image sensor circuits and can
be powered down if an external ADC is used. The conversion
takes place at the falling edge of the clock and the output pins
can be disabled to allow operation of the device in a bus
structure.
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