Intrinsix has developed a Digital Focal Plane Array (DFPA) architecture based on a novel piecewise linear Log2 ADC (LADC) with “lossless” analog compression which enables ultra-high dynamic range ROICs that use less power than other extended dynamic range technologies. The LADC provides dynamic range of 126dB with a constant 75dB SNR over the entire frame. The companding 13bit mantissa, 3bit radix per pixel LADCs compress the 21bit signals into efficient 16 bit data words. The Read Out IC (ROIC) is compatible with most IR and LWIR detectors including two-color SLS (photodiode) and uBolometers. The DFPA architecture leverages two (staggered frame prime and redundant) MIPI CSI-3 interfaces to achieve full HD DFPA at 1000 frames/sec; an equivalent uncompressed data rate of 100Gb/sec. <p> </p>The LADC uses direct injection into a moderate sized integrating capacitor and several comparators create a stream of multi-bit data values. These values are accumulated in an SRAM based log2ALU and the radix of the ALU is combined with the data to generate a feedback current to the integrating capacitor, closing the delta loop. The integration time and a single pole low pass IIR filter are configurable using control signals to the log2ALU. The feedback current is at least partially generated using PWM for high linearity.
In many high dynamic range applications, Sigma-Delta modulator (SDM) architectures have displaced most other architectures for analog to digital conversion (ADC). SDMs have not typically been applied to ROIC applications due to the interaction of spatial discontinuities and the temporal bandwidth limitation of the SDM. By using a novel serpentine readout sequence, we have reduced the temporal bandwidth and enabled application of SDM technology for high dynamic range Focal Plane Arrays (FPA). In addition, it is reconfigurable on-the-fly for a power vs. Signal to Noise plus Distortion Ratio (SNDR) tradeoff without “binning” or reducing the pixel pitch. This technique has been applied to enable low power foveal imaging. This reconfigurable ADC has been coupled with a low noise extended dynamic range photodiode input stages.