A digital output readout circuit with substrate temperature and bias heating compensation for uncooled micro-bolometer infrared focal plane arrays

Abstract

Uncooled micro-bolometer FPAs (focal plane arrays) are influenced by substrate temperature and bias heating effect seriously. When the substrate temperature of the FPA changes greatly, the output and the responsivity of the FPA will vary a lot, thus the images’ quality is poor without the substrate temperature and bias heating effect compensation. In this paper, a new substrate temperature compensation method is proposed, which is completed during analog-to-digital converting with a 12-bit ADC (analog-to-digital converter), and the bias heating effect is canceled by trimming blind bolometers with on-chip DAC (digital-to-analog converter). The simulation result presents the achievable substrate temperature compensation range is about 80K. The proposed structure has been adopted in a readout circuit and successfully fabricated with 0.5μm CMOS process. For normal temperature scene (300K), the digital output only changes 16% when the substrate temperature changes from 253K to 333K. And the equivalent analog output only changes 546.2mV with a 3.4V output swing. As a result, the scene DR (dynamic range) does not change rapidly along with the variation of the substrate temperature and the images’ quality is improved greatly.