Readout integrated circuits

(under development sep 15)

Readout integrated circuit (ROIC) is an electrical circuit multiplexer that mechanically and electrically interfaces or couples to a focal plane array (FPA) sensor/detector serving to function as a voltage buffer which measures or reads individual FPA outputs (sensor data or information) that are driven by incident electromagnetic energy on each and every individual input FPA unit cell or detector and transforms or transmits the sensor data to external electronics. A typical FPA may be composed of 512 columns by 512 rows of individual (assuming no crosstalk) unit cells or pixels having a physical size of 30um by 30 um which define the image frame of the electromagnetic energy incident on the surface. The function of the ROIC is to scan the 512 by 512 array, not unlike a raster scan, in such a way as to sychronously read and bring together in a formatted way all the pixel outputs from the FPA into an appropriate lower impedance electrical circuit for video transmission and processing. Each unit cell detector output responds (gain) to a limited range of wavelengths of the electromagnetic energy incident upon the input, thereby defining the image as infrared, visible, x-ray, etc. The ROIC inputs are compsed of a source follower FET topology (voltage buffer) such as to transform large unit cell output impedance to low input impedance to drive a transmission via (several hundreds of pF) of the unit cell output response. Each unit cell is given a fixed amount of time (integration time) to sample the incident electromagnetic energy before being readout, not unlike a sample and hold circuit.

The interface of the readout to the array is composed of hybridized indium dots for each and every unit cell-to-source follower interface. For example, GaN detector arrays are hybridized to a Si ROIC using flip chip bonding technology.

Scanning the array can be done in various ways. Several methods exist, including: snapshot; fowler; sampling up the ramp. Integration and readout modes includes integrate-while-readand integrate-then-read.

The opposite use of a readout IC (ROIC) is the readin IC (RIIC) which is used to produce or simulate images in a focal plane array. The analogous image system using a RIIC for image simulation is the television image process. Image simulation is used for hardware-in-the-loop (HIL) testing purposes.

ROIC components

Row shift register; zero reset clock;

References and external links

* Indigo [http://www.corebyindigo.com/products/roic.cfm]
* IOP [http://www.iop.org/EJ/article/0268-1242/21/2/002/sst6_2_002.html]
* Semiconductor Complex Limited [http://www.sclindia.com/news/ROIC.pdf]