A New CMOS Read-out IC for Uncooled Microbolometer Infrared Image Sensor

Abstract

An uncooled microbolometer image sensor, used in an IR image sensor, is made by a micro electro mechanical systems (MEMS) process, so the value of the microbolometer resistor has a process variation. Also, the reference resistor, which is used to connect to the microbolometer, is fabricated by a standard CMOS process, and the difference between the values of the microbolometer resistor and the reference resistor generates an unwanted output signal for the same input from the sensor array. In order to minimize this problem, a new CMOS read-out integrated circuit (ROIC) was designed. Instead of a single input mode, a differential input mode scheme and a simple method to compensate the resistor value are proposed. Using results from a computer simulation, it is observed that the output characteristic of the ROIC was improved and the effect of the process variation was decreased without using complex compensation circuits. Based on the simulation results, a prototype device including an ROIC that was fabricated by a standard 0.25um CMOS process and a microbolometer with a 16 x 16 sensor array was fabricated and characterized.

Design of Current-Type Readout Integrated Circuit for 160 × 120 Pixel Array Applications

“…Similarly, when the A<0>-A<159> switches are sequentially turned on, the active bolometer resistance ACT R is connected to the current source to generate voltage as described by (2).…”

“…The reference bolometer signal is disconnected after the reference bolometer output signal is stored, and an active bolometer output signal ACT sig V − , as described by (2), is sent to the 1 M gate. At this time, switch 2 S is turned on and the DC-level shifted voltage is saved to DATA C after passing through the source follower containing in the DDS stage, once again pass through the source follower when switch 3 S is turned on to generate voltage outputs to the negative and positive terminals of the VGA stage, as shown in (3) and (4), respectively.…”

“…At this time, switch 2 S is turned on and the DC-level shifted voltage is saved to DATA C after passing through the source follower containing in the DDS stage, once again pass through the source follower when switch 3 S is turned on to generate voltage outputs to the negative and positive terminals of the VGA stage, as shown in (3) and (4), respectively.…”

“…Existing uncooled-type ROICs for infrared sensors are mainly designed with a fixed voltage bias in the input structure [2,3]. In this paper, the input structure of the proposed fixed current-type ROIC is removed in the integrator to simplify its input structure compared to that of the conventional fixed voltage-type ROIC circuit.…”