A Logarithmic CMOS Image Sensor with Adjustable Photo-response

Using logarithm is always a good strategy for representing a high dynamic range signal. However, despite the potentially huge market for any high dynamic range camera, the conventional logarithmic approach using a MOSFET operating in subthreshold mode suffers from low sensitivity especially at low light levels. In this work, a novel high dynamic range pixel with logarithmic response is proposed. Through using an in-pixel comparator and designing the proper reference voltage, up to 110dB dynamic range can be achieved from the measurement results. In addition, there are two major advantages over conventional logarithmic pixel: The first advantage is that the output signal from this pixel is more immutable to temporal noise owing to output voltage swing is enlarged from 0.3V to 2V using 0.35μm process. The other advantage is that the dynamic range can be adjusted by using different shaped reference voltage. Thus, different photo responses for certain applications can be chosen by circuit designers or even users instead of limiting by process.