Current Input Pixel-Level ADC with High SNR and Wide Dynamic Range for a Microbolometer

Area of Science:

• Electrical Engineering
• Materials Science
• Optics

Background:

• Two-dimensional medium wavelength infrared (MWIR) microbolometer arrays are crucial for thermal imaging applications.
• Existing readout circuits face limitations in signal-to-noise ratio (SNR) and charge handling capacity.
• Optimizing unit cell circuits is key to improving overall array performance and reducing power consumption.

Purpose of the Study:

• To investigate and enhance a readout circuit for MWIR microbolometer arrays.
• To improve the signal-to-noise ratio (SNR) and charge handling capacity of the unit cell.
• To enable longer integration times and maintain performance under low power supply voltages.

Main Methods:

• A current input pixel-level analog-to-digital converter (ADC) was implemented within the readout circuit.
• The integrator's charge handling capacity was extended to maximize integration time.
• The circuit was fabricated using a 0.35-μm 2-poly 4-metal CMOS process for a 640 × 512 array with 40 μm × 40 μm pixels.

Main Results:

• The pixel-level ADC design significantly improved SNR and charge handling capacity.
• Extended integration time was achieved, independent of input current magnitude and low voltage.
• The fabricated array demonstrated a peak SNR of 77.1 dB and a dynamic range of 80.1 dB.
• Power consumption was remarkably low at 0.62 μW per pixel.

Conclusions:

• The developed readout circuit with a pixel-level ADC offers superior performance for MWIR microbolometer arrays.
• The design effectively addresses limitations in SNR and charge handling, crucial for advanced thermal imaging.
• This advancement contributes to more efficient and high-performance infrared sensor technology with low power demands.