ACS-1024-LG Photon Vision Systems, Inc., ACS-1024-LG Datasheet - Page 7

• Manufacturer Part Number: ACS-1024-LG
• Description: Image Sensor, CMOS|CCD, 1026x1026 Pixels, 132pin LCC
• Manufacturer: Photon Vision Systems, Inc.

OPERATIONAL DESCRIPTION:
For simplicity, all of the operational descriptions will specify only signal names not their origin, with the understanding that
each signal referenced may originate from the Controller or the user depending upon the Master Slave mode.
CONTROLLER
In the Master mode the ACS utilizes a complex state machine (heretofore the Controller) to control all events and operation.
By use of the N_CS, N_WR, ADDX and the REG_DATA_X inputs the user may load configuration and operational
information into on chip registers that are accessed by the Controller. The ACS uses a set of shadow registers to store
incoming data allowing the user to write data at any time. The data from these registers is transferred to the Controller at the
beginning of each frame cycle, therefore any data written to the ACS will take effect and be synchronized with the next frame.
Also by use of the aforementioned inputs, the user may read register data out of the Controller.
PIXELS
The ACS pixels are comprised of a Photo Diode (PD) which, when in integration, produces a current proportional to the
amount of incident light. The PD is connected through a field effect transistor (FET) switch to a capacitor or Storage Site
(SS). Another FET switch connects the PD and SS to a reset bias that is supplied to the pixel. The operation of these two
switches controls the integration and reset of the pixel. Reset and integration may be performed on a row-by-row basis or
globally. Signals CRST, TX, ROW RST and ROW XFER enable global reset, global transfer; row reset and row transfer
respectively.
CDS TIMER
The ACS performs Fixed Pattern Noise (FPN) cancellation by use of on chip Correlated Double Sampling (CDS). The CDS
sequence begins by the selection of a given row. Once the data on the Row Address Bus is valid, ROW_LOAD must be
strobed to latch the address data. Next, a Row Load Pulse (RLP) must be sent to the CDS timer to begin the CDS process.
Upon the completion of CDS, the CDS Timer issues an End Of CDS (EOC) indicating that there is valid data on the video
output bus. As the ACS is randomly addressable, the CDS timer has no knowledge of the size of the array area to be readout.
The ACTIVE signal must be set TRUE and stay TRUE until readout of the desired pixels is completed. After readout
completion releasing the ACTIVE signal, allows the CDS timer to finish end of row events.
PVS BUS OUTPUT/READOUT
After completion of CDS and the issuance of ACTIVE, valid data is available on the video bus. To accomplish readout, an
address is placed on the Column Address Bus, COL_LOAD must be strobed, at which time the data from the first pixel in the
desired array is available. The address and COL_LOAD sequence are repeated until the last pixel in the row has been read.
CDS/READOUT MODES:
The ACS has 4 modes of integration-readout operation, Mode 0 or standard rolling shutter mode (conventional CDS), Mode 1
or reverse CDS rolling shutter, Mode 2 or adaptive exposure mode (non-destructive readout) mode, and Mode 3 or full frame
shutter (snapshot shutter) mode.
MODE 0
This mode is referred to as Standard or Conventional CDS (CCDS). In this mode (recall the pixel structure) after integration
the SS is sampled, then the PD value is transferred and the SS re-sampled. The first sample is subtracted from the second in a
differential amplifier and the net result is video minus noise.
MODE 1
Mode 1 is referred to as reverse or Quasi-CDS (QCDS). Under high overload conditions, this mode provides superior
isolation from saturation artifacts. When performing full frame transfer functions, QCDS is required. In QCDS the global
transfer switch is always closed, thus the PD and SS are the same node electrically. During readout, the combined node is
sampled, then reset takes place and the node is re-sampled. The differential amplifier yields the first minus the second.
Photon Vision Systems, Inc.
Product DATASHEET ACS PDS0003 Subject to change without notice. Page 7 of 26
Copyright© 2002 Rev A